\\over \\sim \\;$}\n\\def\\rfe{R$_{\\rm FeII}$}\n\\def\\ai{A.I.($\\frac{1}{4}$)\\/}\n\\def\\aox{$\\alpha_{ox}$\\/}\n\\def\\gs{$\\Gamma_{\\rm soft}$}\n\\def\\gh{$\\Gamma_{\\rm hard}$}\n\\def\\G{$\\Gamma$}\n\\def\\ne{n$_{\\rm e}$\\/}\n\\def\\ergss{ergs s$^{-1}$}\n\\def\\simgt{\\lower.5ex\\hbox{\\gtsima}} % > over MMM\n\\def\\bv{{\\bf $\\bigvee$}\\/}\n\\def\\qu{{$\\lambda$ 1400}}\n\\def\\h{$h^{-1}$}\n\\def\\hii{{\\sc Hii\\/}}\n\\def\\hi{{\\sc Hi\\/}}\n\\def\\a{$\\alpha$}\n\\def\\ha{{\\sc H}$\\alpha$}\n\\def\\nv{{\\sc Nv}$\\lambda$1240}\n\\def\\civ{{\\sc{Civ}}$\\lambda$1549\\/}\n\\def\\civnc{{\\sc{Civ}}$\\lambda$1549$_{\\rm NC}$\\/}\n\\def\\civbc{{\\sc{Civ}}$\\lambda$1549$_{\\rm BC}$\\/}\n\\def\\cmsq{cm$^{-2}$\\/}\n\\def\\cm3{cm$^{-3}$\\/}\n\\def\\md{$\\dot{\\rm M}$}\n\\def\\rg{$\\rm R_{\\rm g}$}\n\\def\\hb{{\\sc{H}}$\\beta$\\/}\n\\def\\hg{{\\sc{H}}$\\gamma$\\/}\n\\def\\hbbc{{\\sc{H}}$\\beta_{\\rm BC}$\\/}\n\\begin{document}\n\\maketitle\n\\section{Introduction \\label{sec:intro}}\n\nThe Broad Line Region (BLR) in Active Galactic Nuclei (AGN) is unresolved with present\nday imaging detectors and it will remain so for the foreseeable future. This is why\n``one quasar spectrum is really worth a thousand images'' as stressed by Gary Ferland\nat this meeting. In response we would add that {\\em a thousand spectra are better than\none average spectrum}. Understanding the diversity in optical spectroscopic properties\nof AGN is the key to any realistic AGN modeling \\cite{bg92,smd}. The ideal to\nreconstruct the BLR velocity field from a single profile is not realistic \\cite{pen90}.\n\nDetermination of BLR structure and kinematics can be approached in two ways. It has\nbeen recognized for a long time that strong broad and narrow emission lines coming from\nboth high and low ionization species are present in Seyfert galaxies and quasars. This\nis considered a defining spectroscopic property of AGN. Restricting attention to broad\nlines: a) typical (i.e., strongest and most frequently observed) high ionization lines\n(HIL: ionization potential $\\simgt$ 50 eV) are \\civ\\ \\heii\\ and \\heiiuv\\ lines; while\nb) observed low ionization lines (LIL: ionization potential $\\simlt $ 20 eV) include\n\\hi\\ Balmer lines, \\feii\\ multiplets, \\mgii, and the Ca{\\sc ii}\\ IR triplet.\n\nThe first approach involves the study of line variability in response to continuum\nchanges. This approach has been pursued through a number of successful monitoring\ncampaigns using Reverberation Mapping (RM) techniques. RM requires a large amount of\ntelescope time and, consequently, has been achieved only for a handful of sources. RM\nconfirms that photoionization is the main heating process in the BLR and that a large\npart of the BLR is optically thick to the ionizing continuum (e. g. \\pcite{baldwin97}).\nRM studies have quantified a main difference between HIL and LIL; HIL respond to\ncontinuum changes with a time delay of a few days while the LIL respond with a delay of\ntens of days. This implies that the LIL are emitted at larger distance from the\ncontinuum source (\\pcite{ulr,kor95}. An exhaustive list of reference can be found in\n\\pcite{smd}). RM applied to line profiles suffers from uncertainty in our knowledge\nabout the physics of continuum and broad line formation, so that conflicting models can\nstill describe the same lag times \\cite{pen91,wanpet96}.\n\nThe second approach involves statistical analysis of large samples of line profiles\nwhich differ because of properties that may affect the BLR structure, for example\nsamples of radio quiet (RQ) and radio loud (RL) AGN. Statistical studies can be done\nfor a single line or by comparing lines sensible to different physical parameters (e.g.,\nstrongest LIL and HIL). The statistical approach, on which we will focus here, is more\nempirical and therefore requires a conceptual framework for interpretation. This\napproach is often criticized as relying on several assumptions including that the\nprofile variability does not influence profile shapes and that the non-simultaneity of\nthe observations of LIL and HIL are unimportant. Actually as the size of high quality\ndata samples grow these effects become less and less important.\n\n\\section{Baring the Broad Profiles \\label{bare}}\n\nThe collection of moderate resolution (\\l/$\\Delta$\\l $\\sim 10^3$) optical and UV\nspectra of good quality (S/N $\\simgt$ 20 in the continuum) has become possible only in\nrecent years thanks to the widespread use of CCD detectors and the unprecedented\nsensitivity and resolution of the UV spectrographs on board HST. For practical\npurposes, \\hi\\ \\hb\\ and \\civ can be considered representative of HIL and LIL\nrespectively. They are also the best lines for statistical studies because they permit\ncomparison in the same sources out to z=1.0. The linearity of response of the\ncurrently employed detectors has made possible a reliable correction for emission\nfeatures contaminating \\hb\\ and \\civ, which are: (1) \\feii\\ emission; significant\n\\feiiuv\\ emission contaminates the red wing of \\civ, and has been identified in I Zw 1\nby \\pcite{m96} and later confirmed by \\pcite{lao97}; (2) \\heii\\ emission for \\hb, and\n\\heiiuv\\ + \\oiiiuv\\ for \\civ; (3) \\oiii\\ for \\hb; (4) narrow component, present in\nseveral cases in both \\hb\\ and \\civ.\n\n\n\\civ\\ often shows a narrow core with FWHM $\\sim$ 1000-2000 \\kms, which is\nsystematically broader than the narrow component of \\hb\\ (\\hbnc). The separation\nbetween the broad component \\civbc\\ and the core component is often ambiguous. This\ncore however shows no shift with respect to the AGN rest frame \\cite{brot94}, no\nvariations \\cite{turla}, and correlates with \\oiii\\ prominence \\cite{franc92}. It can\ntherefore be ascribed to the NLR and considered as the narrow line component of \\civ\\\n(\\civnc). The different width between \\civnc\\ and \\hbbc\\ can be understood in terms of\ndensity stratification \\cite{sm99} without invoking an additional emitting region such\nas the so-called ``intermediate line region''. Even if \\civnc\\ fractional intensity is\nsmall ($\\sim$ 10\\%), and in some cases obviously absent, failure to account for \\civnc\\\nhas led to the erroneous conclusions that FWHM \\civbc\\ $>$ FWHM \\hbbc\\ and that the\n\\civ\\ peak shows no shift with respect to \\hb\\ \\cite{cb96}.\n\n\\section{A DIFFERENT BLR STRUCTURE IN RADIO LOUD AND RADIO QUIET AGN? \\label{struct}}\n\n\\scite{m96} made a comparison between \\civbc\\ and \\hbbc\\ for a sample of 52 AGN (31\nRL). They presented measures of radial velocity for the blue and red sides of \\hbbc\\\nand \\civbc\\ at 5 different values of fractional intensity which provide a quantitative\ndescription of the profiles. The reference frame was set by the measured velocity of\n\\oiii$\\lambda$5007$\\rm{\\AA}$ (IZw1 was the only exception). Standard profile parameters\nlike peak shift, FWHM, asymmetry index and curtosis can be extracted from these\nmeasures. Representative profiles constructed from the {\\em median values} of \\civbc\\\nand \\hbbc\\ $v_r$\\ are reproduced in the left panels of Fig. \\ref{fig:rq} and\n\\ref{fig:rl} for the radio quiet (RQ) and radio loud (RL) samples respectively.\n\\begin{figure}\n %\\begin{center}\n \\leavevmode\n \\includegraphics[width=\\columnwidth, height=8cm]{fig01.eps}\n% \\includegraphics[width=\\textwidth, height=10cm]{Fig01dd.eps}\n\\caption[]{Profiles of \\civbc\\ (solid lines) and \\hbbc\\ normalized to the same peak\nintensity and constructed from median values of the radial velocities measured on the\nblue and red sides of the profiles for the 21 RQ AGN of \\scite{m96} (left panel).\nEmission line profiles of \\civ\\ (middle panel) and \\hb\\ (right panel) of the prototype\nNLSy1 galaxy I Zw 1, adapted from \\scite{m96}. The thick and the dotted lines trace \\hb\\\nand \\oiii\\ after \\feiiopt\\ (dashed line) subtraction. \\label{fig:rq}}\n %\\end{center}\n\\end{figure}\n\n\\civbc\\ is broader than \\hbbc in both RQ and RL samples and it is {\\em almost always}\nblueshifted relative to \\hbbc. However Fig. \\ref{fig:rq} and Fig. \\ref{fig:rl} show\nsignificant differences between RQ and RL AGN. In RQ AGN, \\civbc\\ is significantly\nblueshifted with respect to the source rest frame while \\hbbc\\ is symmetric and\nunshifted. Contrarily in RL AGN \\civbc\\ is more symmetric, while \\hbbc\\ is shifted to\nthe red at peak intensity and redward asymmetric as well (the median profile\ncorresponds to the type AR,R according to \\pcite{sul89}). There are two important\nresults which are not displayed in the Figures: (i) in RQ AGN, \\civbc\\ blueshifts are\napparently uncorrelated with respect to any \\hbbc\\ line profile parameter and the\nlargest \\civ\\ blueshifts are associated with the lowest W(\\civ); (ii) in RL AGN, on the\ncontrary, \\civbc\\ and \\hbbc\\ line profile parameters (FWHM and peak shift) appear to be\ncorrelated. Asymmetry index of \\civbc\\ and \\hbbc, even if not correlated, shows a clear\ntrend toward asymmetries of the same kind (symmetric or redward asymmetric). These\nfindings on \\civbc\\ have been confirmed by other authors (\\pcite{wills95}, save the\ndifference in terminology and line profile decomposition) and especially by an analysis\nof archival HST/FOS observations which have become publicly available after 1995\n\\cite{sul20}.\n\nThe LIL and HIL emitting regions are apparently de-coupled in at least some RQ\nsources. The ``de-coupling'' is well seen in I Zw 1, the prototype Narrow Line Seyfert\n1 Galaxy (NLSy1; see Fig. \\ref{fig:rq}). The \\hb\\ profile is very narrow, slightly\nblueward asymmetric and unshifted with respect to the rest frame defined by 21 cm\nobservations, while the \\civ\\ profile is almost totally blueshifted. At least in the\ncase of I Zw 1 the distinction between LIL and HIL emitting regions appears to be\nobservationally established (it was actually suggested because of the difficulty to\nexplain the relative strengths of LIL and HIL emission using a photoionized ``single\ncloud;'' \\pcite{cs88}). There is a very important zeroth-order result here: since I Zw\n1 is a strong \\feiiuv\\ emitter, we have HIL \\civ\\ and LIL \\feiiuv\\ in the same\nrest-frame wavelength range. We see that \\feiiuv\\ is obviously unshifted (this can be\nvery well seen by shifting an \\feiiuv\\ template to the peak radial velocity of \\civ).\nThis result disproves models that see an (unknown) wavelength dependent mechanism\naccounting for the quasar broad line shifts relative to the quasar rest frame.\n\nRL AGN apparently mirror RQ AGN in a curious way: \\civbc\\ is more symmetric, while\n\\hbbc\\ shows preferentially redshifted profiles and increasingly redward asymmetries.\nLarge peak redshifts ($v_r \\simgt 1000$ \\kms, as in the case of OQ 208, Fig.\n\\ref{fig:rl}) are rarely observed; \\hbbc\\ peak shifts are usually small ($\\Delta\nv_r$/FWHM $\\ll$ 1, median profile of Fig. \\ref{fig:rl}). RL \\civbc\\ and \\hbbc\\ data\nleave open the possibility that both lines are emitted in the same region. \\civbc\\\nshows a red-wing (very evident in the latest, higher S/N spectra analyzed by\n\\scite{sul20}), which cannot be entirely accounted for by \\feiiuv emission. It is\ninteresting to note that superluminal sources with apparent radial velocity $\\beta_{\\rm\napp} \\sim 5-10$~ (whose radio axis is probably oriented close to the line of sight in\nthe sample of \\scite{m96} show very strong \\civ\\ redward asymmetries, low W(\\civ) and\nW(\\hbbc). This result suggests that redshifts are maximized in RL objects at\n``face-on'' orientation (we assume that any disk is perpendicular to the radio axis).\n\n\\section{NLSy1 NUCLEI ARE NOT A DISJOINT RQ POPULATION}\n\nNLSy1 are neither peculiar nor rare. The 8$^{th}$\\ edition of the \\scite{veron98}\ncatalogue includes 119 NLSy1 satisfying the defining criterion FWHM Balmer $\\simlt$\n2000 \\kms. They account for $\\approx 10$\\%\\ of all AGN in the same redshift and\nabsolute magnitude range. Attention toward NLSy1 remained dormant after their\nidentification as a particular class \\cite{op85} until it was discovered that they may\nrepresent $\\approx$1/3--1/2 of all soft X-ray selected Seyfert 1 sources (e. g.,\n\\pcite{grupe98}). NLSy1 are also apparently favored in AGN samples selected on the\nbasis of color. They account for 27\\%\\ of the RQ \\scite{bg92} sample, probably because\nof an optical continuum that is steeply rising toward the near UV. NLSy1 do not occupy\na disjoint region in parameter space. They are at an extremum in the FWHM(\\hb) vs.\n\\rfe\\ (=I(\\feii \\l 4570/I(\\hbbc)) and in the ``Eigenvector 1'' parameter spaces\n\\cite{bg92,bf99,smd}. Also, the soft X-ray spectral index \\gs\\ shows a continuous\ndistribution which includes NLSy1 at the high end \\cite{wang96,smd,sul20}.\n\n\\begin{figure}\n %\\begin{center}\n \\leavevmode\n \\includegraphics[width=\\columnwidth, height=8cm]{fig02.eps}\n% \\includegraphics[width=\\textwidth, height=10cm]{Fig01dd.eps}\n \\caption[]{Left panel: Profiles of \\civbc\\ (solid lines) and \\hbbc\\ normalized to the same\n peak intensity and constructed from median values of the radial velocities measured on\n the blue and red sides of the profiles for the 31 RL AGN of \\scite{m96}.\n Middle panel: \\hb\\ spectrum of OQ 208, showing a single, widely displaced \\hbbc\\ peak (adapted from \\pcite{m93}).\n Right panel: \\ha\\ profile of the prototype of ``wide-separation double peakers'' Arp 102B.\n Unpublished spectrum obtained at the 1.82 m telescope of the Asiago observatory on March 25, 1989.\n The thick solid line traces \\hbbc.}\n \\label{fig:rl}\n %\\end{center}\n\\end{figure}\n\nOrientation can easily explain much of the RQ phenomenology observed by \\scite{m96}. I\nZw 1 can be considered as an extremum with an accretion disk seen face-on\n(i$=0^\\circ$), and an outflowing wind observed along the disk axis. We can infer that\nthe opening angle of any \\civ\\ outflow is probably large (i. e., the wind is quasi\nspherical) because \\civ\\ profiles like I Zw 1 are rare. Other NLSy1 show low W(\\civ),\nand strong \\feiiopt, but do not always show large \\civ\\ blueshifts \\cite{rp97}.\nNonetheless, it is still possible that NLSy1 may be structurally different from other\nRQ AGN. If the soft X-ray excess of NLSy1 is due to high accretion rate, then a slim\naccretion disk is expected to form \\cite{abram88}. Line correlations presented in\n\\cite{sul20} appear to hold until FWHM(\\hb)$\\simlt$ 4000 \\kms. For FWHM$\\simgt$ 4000\n\\kms line parameters appear to be uncorrelated however it is still unclear it is at\npresent unclear because of the difficulty in measuring weak and broad \\feiiopt sources\nand/or because of a BLR structural difference. This limit may be related to the\npossibility of sustaining a particular disk structure and an HIL outflow. A second\nparameter, independent from orientation is needed to account for the FWHM(\\hbbc) vs\n\\rfe\\ vs \\gs\\ sequences (see \\pcite{smd,sul20} for a detailed discussion).\n\n\n\\section{Inferences on BLR Models for RQ AGN}\n\nModels developed almost independently of the data through the 80's and early 90's.\nThe situation has now changed because of three main developments: (1) the ``Eigenvector\n1'' correlations allow a systematic view of the change in optical emission line\nproperties for different classes of AGN \\cite{bg92,bf99,smd}; (2) the \\civ\\ - \\hb\\\ncomparison has yielded direct clues about the structure of the BLR \\cite{m96,sul20} and\n(3) data collected for RM projects provide a high-sampling description of line\nvariations. For instance, binary black hole scenarios \\cite{gask96} were recently\nchallenged by the failure to detect the radial velocity variations expected from\nprevious observations and model predictions \\cite{eracl97}.\n\nA model in which \\civ\\ is emitted by outflowing gas (e.g. a spherical wind) while\n\\hbbc\\ is emitted in a flattened distribution of gas (observed in a direction that\nminimizes velocity dispersion) such as an optically thick disk (obscuring the receding\nhalf of the \\civ\\ flow, \\pcite{liv97}) or at the wind base is immediately consistent\nwith the I Zw 1 data. The big question is whether the results for I Zw 1 can be\nstraightforwardly extended to other RQ AGN.\n\nAn accretion disk (AD) provides a high density and high column density medium for\n\\feii\\ production (e. g. \\pcite{dj92}), and possibly other low ionization lines such as\nCaII (e. g. \\pcite{dd99}). AD avoid conflict with the stringent restrictions on line\nprofile smoothness imposed by the first extremely high s/n Balmer line observations\n(\\pcite{arav97,arav98}) of -incidentally- two NLSy1. They place a lower limit of\n(10$^{7-8}$) on the number of discrete emitters needed to explain the observed profiles.\n\nWinds arise as a natural component of an AD model when the effects of radiative\nacceleration are properly taken into account \\cite{murray95,mc98} or when a\nhydromagnetic or hydrodynamic treatment is performed \\cite{bottorff97,williams99}. A\nsignature of radiative acceleration is provided by observations of ``double troughs'' in\n$\\approx \\frac{1}{5}$ of BAL QSOs i. e., of a hump in the absorption profiles of \\nv\\\nand \\civ\\ at the radial velocity difference between \\lya\\ and \\nv, 5900 \\kms. Such a\nfeature indicates that \\lya\\ photons are accelerating the BAL clouds (\\pcite{arav94},\nand references therein). Additional evidence is provided by the radial velocity\nseparation in the narrow absortion components of \\lya\\ and \\nv\\ which show the same\n$\\Delta v_r$\\ of the two doublet components of \\civ\\ (e. g. \\pcite{wampler91}).\n\n\\section{The Trouble With Bare Accretion Disks and Bipolar Flows}\n\nRelativistic Keplerian disks \\cite{ch89,sb93} may explain unusual profile shapes (e.g.\ndouble-peaked profiles of Balmer emission lines; \\pcite{eh94,sul95}). Uniform\naxisymmetric disk models produce double-peaked line profiles with the blue peak\nstronger than the red peak because of Doppler boosting, a feature that is not always\nobserved in these already rare profiles. To solve this problem, \\scite{sb95} and\n\\scite{eracl95}, proposed that the lines can originate in an eccentric (i.e.\nelliptical) disk. Simple disk illumination models can also produce single peaked LIL,\nprovided they are produced at large radii ($\\simgt 10^3$\\ gravitational radii) or that\nthe disk is observed at small inclination \\cite{dc90,rokaki92,sul98}. The first of these\nconditions may be met in all NLSy1 galaxies; both of them seem to be met in I Zw 1.\n\nAside from NLSy1 sources, there is general disagreement between observations and model\npredictions for externally illuminated Keplerian disks in a line shift-- asymmetry\nparameter space \\cite{sul90}. Only a minority ($\\simlt$ 10 \\%) of RL and a handful of\nRQ AGN show double peaked Balmer lines suggestive of a Keplerian velocity field\n\\cite{eh94,sul99}. Double-peakers (e. g. Arp 102B in Fig. \\ref{fig:rl},\nFWHM(\\hbbc)$\\simgt$10000 \\kms) cannot be like the classical cases because the line\nwidths are much smaller. The peaks often vary out of phase (Arp 102B: \\pcite{mp90}, 3C\n390.3: \\pcite{zheng91}). Double peaks (NGC 1097) \\cite{sb93,sb95} or one of the peaks\n(Pictor A) \\cite{sul95} sometimes appear quite suddenly. Profile variability studies of\nBalmer lines force us to introduce second order modifications to the basic scheme, such\nas: eccentric rings and precession \\cite{eracl95,sb97}, inhomogeneities such as\norbiting hot spots \\cite{zheng91}, and warps \\cite{bachev99}. Not even these {\\em\nepicycles} are always capable of explaining the observed variability patterns. Even if\nelliptical AD models do well in explaining the integrated profiles, they face important\ndifficulties in explaining variability patterns.\n\nA serious problem for AD models of emission lines is emerging from spectropolarimetric\nobservations. If profile broad line shapes are orientation dependent then, in\nprinciple, the profile shape in polarized light will depend on the distribution of the\nscatterers relative to the principal axis and to our line of sight. Early\nspectropolarimetric results showed a discrepancy with the simple disk +\nelectron-scattering-dominated atmosphere models, which predicted polarization\nperpendicular to the radio axis. The observed polarization is low, parallel to the disk\naxis, and shows no statistically significant wavelength dependence \\cite{anton88}.\nRecently \\scite{anton96} and \\scite{corbett98} included double-peakers in their\nsamples, and obtained troublesome results for disk emission models because the\npolarized \\ha\\ profiles are centrally peaked \\cite{corbett98}. They investigated the\ncase of disk emission where the scattering particles are located above and below an\nobscuring torus, along its poles. This ``polar scattering model'' is successful in\nexplaining the polarized profiles {\\em but not the position angle of the polarization\nvector}.\n\nThe same polarization studies indicate that the {\\em only} scenario that can account\nfor both the shapes of the scattered line profiles and the alignment of the optical\npolarization with the radio jet in wide separation double peakers like Arp 102B (Fig.\n\\ref{fig:rl}) involves a {\\em biconical} BLR within an obscuring torus. \\ha\\ photons\nemitted by clouds participating in a biconical flow are scattered towards the observer\nby dust or electrons in the inner wall of the surrounding torus. The particular case of\nbiconical outflow was first developed to reproduce observed profiles by\n\\scite{zheng90}. This model has been successfully applied to fit observed profiles in\ndouble-peaked objects \\cite{zheng91,sul95}.\n\nDouble peaked or single blueshifted peak LIL profiles fitted with bi-cone outflow\nmodels require that the receding part of the flow is also seen. Self-gravity may be\nimportant beyond $\\sim 1$ pc, and the disk may be advection-dominated and optically\nthin \\cite{liv96}. Recent work by \\scite{sh99} models the vertical structure of AD and\nthe origin of thermal winds above AD. They not only find that a wind powered by a\nthermal instability develops in all disks with certain opacity laws but also that in\ndisks dominated by bremsstrahlung radiation, a time-dependent inner hole develops below\na critical accretion rate. This scenario provides a natural explanation for transient\ndouble-peakers, such as NGC1097 \\cite{sb95,sb97}, but low accretion rate is a\nrequirement for {\\em both} advection dominated disks and hole formation.\n\n\\scite{sul95} explored the idea that the double-peaked emitters represent a\ngeometrical extremum where an outflow is viewed close to pole-on. However,\ndouble-peakers are associated with double-lobe radio-sources suggesting that the line\nof sight has a considerable inclination to the axis of the jets. The problem arises\n{\\em only} if the core (pc scale) jets is related to the much larger (100 kpc scale)\njets. There is both theoretical (e. g. \\pcite{valtonen99}) and observational evidence\nagainst this assumption.\n\n\\section{Emission from Clouds Illuminated by an Anisotropic Continuum}\n\nModels based on radiative acceleration of optically thick clouds with small volume\nfilling factor gained wide acceptance in the Eighties (\\pcite{om86} and references\ntherein; see also \\pcite{binette96}). However, problems with cloud confinements and\nstability \\cite{mathews90} have made them increasingly less frequently invoked to\nexplain observations.\n\nFirst RM studies on Balmer lines excluded radial, and favored orbital or chaotic\nmotions (e.g. \\pcite{kg91,kor95}). \\scite{goadw96} applied RM techniques to one of the\nmost extensively monitored objects: NGC 5548. They ruled out radial motions, and found\nthat the \\civ\\ line variations are broadly consistent with a spherical BLR geometry, in\nwhich clouds following randomly inclined circularly Keplerian orbits are illuminated by\nan anisotropic source of ionizing continuum. A RM result favoring Keplerian motion may\nbe approximately correct also for models in which the emitting gas is not bound, such\nas a wind, since most of the emission occurs near the base of the flow, when the\nvelocity is still close to the escape velocity which is similar to the Keplerian\nvelocity \\cite{mc98}.\n\n\\section{Is the disk + wind model applicable to all AGN?}\n\nEmission from a terminal flow can explain the recent observations of Goad et al. 1999\nwho reported that LIL (\\mgii + \\feiiuv) in NGC 3516 do not respond to continuum\nvariations which did induce detectable variability in the HIL (\\lya\\ and \\civ) lines.\nHydromagnetic wind models such as those developed by \\scite{emmering92} and\n\\scite{bottorff97} exhibit these basic properties. A two-zone wind provides another\nscenario for the different origins of LIL and HIL.\n\nTurning to the general population of RL AGN, the predominance of redshifts and redward\nasymmetric profiles is difficult to explain. Several lines of evidence suggest a\nsignificant role of gravitational redshift in RL AGN \\cite{corbin97} possibly related\nto a lower distance (in units of gravitational radii) between BLR and central black\nhole, which may be systematically more massive in RL than in RQ AGN. If this is the\ncase, then a double zone wind may be present also in RL AGN, since \\civbc\\ is still\nsystematically blueshifted with respect to \\hbbc. The ``correlation'' between \\civbc\\\nand \\hbbc\\ parameters could be due to the impossibility of maintaining a radial flow\nalong the disk axis, where a relativistic jet is instead propagating. This will make\nany HIL outflow possible only at lower latitudes over the disk plane, and therefore\nwill produce more similar \\hbbc\\ and \\civbc\\ profiles.\n\n\n\\section{CONCLUSION}\n\nWhile observations support emission from an accretion disk and an associated spherical\nwind in RQ AGN with FWHM(\\hbbc) $\\simlt$ 4000 \\kms, there is not enough observational\nsupport to warrant the same conclusion for RL AGN (and possibly RQ with FWHM$>$4000\n\\kms), although a disk + wind model is a viable possibility also in this case. Wide\nseparation double peakers (mostly RL) do not provide conclusive evidence in favor of\nLIL disk emission; rather, there is evidence against disk emission as well as against\nevery other reasonably simple scenario.\n\n\\acknowledgements DD-H acknowledges support through grant IN109698 from PAPIIT-UNAM. PM\nacknowledges financial support from MURST through grant Cofin 98-02-32, as well as\nhospitality and support from IA-UNAM. We also acknowledge consistent (cycles5-9 AR and\nGO) rejection of proposals to continue this work.\n\n%There are conflicting lines of evidences. It is unclear whether\n%wide separation double-peaks in Balmer lines are due to rotation\n%or to outflow. Their rarity and abnormal line width suggest that\n%they may be a peculiar class in a short-lived phase of their\n%evolution.\n%% When using the rmaacite package, the \\bibitem command should be of\n%% the format:\n%%\n%% \\bibitem[AUTHOR<YEAR>]{KEY}\n%%\n%% so that the \\cite{KEY}, etc. commands will work properly.\n%%\n%% If you are doing the citations manually, then you can just use\n%% `\\bibitem{}' instead. This will give you a warning about\n%% `multiply-defined labels' which you can safely ignore.\n%%\n\\begin{thebibliography}{}\n%\\bibitem[Aretxaga et al.<1999>]{arex} Aretxaga, I., Joguet, B., Kunth, D., Melnick, J. \\& Terlevich, R. 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A. 1991. \\apj, 381, 418\n\\end{thebibliography}\n%\\bibitem[Bally et al.{}<1995>]{p:Bal95}\n% Bally, J., Devine, D. \\& Sutherland, R. 1995, In: S. Lizano \\&\n% J.~M. Torrelles (eds.): {Circumstellar Disks, Outflows and Star\n% Formation}, RMAA (Serie de Conferencias) {1}, 19\n\n\n\n\n\n\\end{document}\n"}],"string":"[\n {\n \"name\": \"dd_submitted.tex\",\n \"string\": \"%%% Sample proceedings article for rmaa.cls\\n%%%\\n%%% Converted to RMAA(SC) style and annotated by Will Henney\\n%%% (04 Oct1999)\\n%% This file contains examples of many of the commands in the LaTeX\\n%% document class rmaa.cls, such as the commands for specifying data\\n%% for the title page and the commands for including postscript\\n%% figures. For more details, you should consult the accompanying\\n%% Author Guide (`rmuser.tex'). A further sample document\\n%% (`rmtest.tex') contains examples of some commands not used in this\\n%% file, eg. for marking up tables. You may also want to use this file\\n%% as a template for your own article.\\n%% Note: This article was originally published in `IAU Symposium 182:\\n%% Herbig-Haro Objects and the Birth of Low-mass Stars',\\n%% ed. B. Reipurth & C. Bertout (Dordrecht: Kluwer). Hopefully, I've\\n%% changed it enough to avoid copyright violation!\\n%% All proceedings articles must begin with the following line\\n\\\\documentclass[proceedings,onecolumn]{rmaa}\\n%%\\n%% The file `rmaa.cls' should be somewhere in your TeX search path\\n%% (e.g, in the current directory, or in a personal or system-wide\\n%% directory of LaTeX packages.\\n%%\\n%% This will not work with old versions of LaTeX: any version\\n%% of LaTeX2e should be OK, but LaTeX209 is too old. If LaTeX\\n%% complains that it doesn't recognise the command `\\\\documentclass'\\n%% then your LaTeX installation needs updating!\\n%% The following package allows one to do the citations\\n%% semi-automatically. It defines the commands \\\\cite{KEY},\\n%% \\\\scite{KEY}, and \\\\pcite{KEY} which respectively produce citations\\n%% in the following styles:\\n%% (AUTHOR YEAR)\\n%% AUTHOR (YEAR)\\n%% AUTHOR YEAR\\n%% For this to work, you need to pay attention to the formatting of\\n%% the `\\\\bibitem's in your `thebibliography ' environment, qv.\\n\\\\usepackage{rmaacite}\\n%% If you would rather do your citations by hand, then comment out the\\n%% above line\\n\\n%% Here, you can put the definitions of your own personal macros.\\n%% All the special commands defined in AASTEX 4.0 (e.g. \\\\ion{}{},\\n%% \\\\gtrsim, \\\\arcsec, \\\\apj, etc) are already defined. I haven't checked\\n%% if there are any new ones in AASTEX 5.0 yet.\\n\\\\newcommand{\\\\thOr}{$\\\\theta^1\\\\,$C~Ori}\\n\\\\newcommand{\\\\zero}{_0}\\n\\\\newcommand{\\\\kms}{\\\\,\\\\mbox{km s$^{-1}$}}\\n\\\\newcommand{\\\\Othree}{[\\\\ion{O}{3}]~5007\\\\AA}\\n\\\\renewcommand{\\\\P}[1]{%\\n\\\\ifnum#1=1\\\\hbox{OW~168--326E}\\\\fi \\\\ifnum#1=2\\\\hbox{OW~167--317}\\\\fi\\n\\\\ifnum#1=3\\\\hbox{OW~163--317}\\\\fi \\\\ifnum#1=5\\\\hbox{OW~158--323}\\\\fi\\n\\\\ifnum#1=0\\\\hbox{OW~171--334}\\\\fi}\\n\\n%%\\n%% The following commands specify the title, authors etc\\n%%\\n\\\\title{The Broad Line Region in Active Galactic Nuclei}\\n\\\\author{D. Dultzin-Hacyan\\\\altaffilmark{1},\\nP. Marziani\\\\altaffilmark{2}, J.W. Sulentic\\\\altaffilmark{3}} \\\\altaffiltext{1}{Instituto\\nde Astronom\\\\'{\\\\i}a, UNAM, M\\\\'exico} \\\\altaffiltext{2}{Osservatorio Astronomico, Padova,\\nItalia} \\\\altaffiltext{3}{Dept. Physics and Astronomy, University of Alabama,\\nTuscaloosa, USA}\\n\\n\\n%%\\\\altaffiltext{1}{Just to see that the affiliation subscripts work OK}\\n%% Note that the \\\\affil{} command is inside the argument of the\\n%% \\\\author{} command and that a short version of the address should go\\n%% here. More complicated author/address examples are discussed in the\\n%% Author Guide (`rmuser.tex') and illustrated in the example document\\n%% `rmtest.tex'\\n%% The full postal addresses are specified here - they will be typeset\\n%% at the end of the article. Here is also the place to put email\\n%% addresses.\\n%\\\\fulladdresses{\\\\item}\\n%\\\\item D. Dultzin-Hacyan: Instituto de Astronom\\\\'\\\\i a,\\n% UNAM, Ap.do Postal 70-264, M\\\\'exico D. F. 04510, M\\\\'exico (deborah@astroscu.unam.mx)\\n%\\\\item P. Marziani: Osservatorio Astronomico di Padova,\\n%Vicolo dell' Osservatorio 5, I--35122 Padova, Italia (marziani@pd.astro.it)\\n% \\\\item J.W. Sulentic: Dept of Physics And Atronomy, Univesity of Alabama,\\n%Tuscaloosa, AL 35487 (giacomo@merlot.astr.ua.edu) }\\n%% Note that the `\\\\fulladdresses' command defines a list-like\\n%% environment, so each separate address must be preceded by the\\n%% `\\\\item' command (here there is only one, since the authors share the\\n%% same address).\\n\\n%% Title/author for running headers\\n\\\\shortauthor{Dultzin-Hacyan et al.} \\\\shorttitle{BLR in AGN}\\n%% These will automatically be converted to upper case in the current\\n%% style.\\n\\n%% No more than 5 keywords, chosen from the standard list\\n\\\\keywords{galaxies: active --- lines: profiles --- quasars: emission lines}\\n\\n\\\\abstract{We review constraints on models of the broad line region that are imposed by\\nobservations of the emission lines in Active Galactic Nuclei. Comparison of high and\\nlow ionization lines in sources with FWHM H$\\\\beta\\\\leq$4000 km s$^{-1}$ points toward low\\nionization line emission produced in a flattened geometry (the accretion disk?) with an\\nassociated high ionization wind. It remains unclear whether these results can be\\nextended to all radio quiet AGN and particularly to radio loud AGN.}\\n\\n\\\\resumen{Revisamos las limitaciones que se pueden imponer a partir de las\\nobservaciones, sobre los modelos de la estructura de las regiones que emiten las lineas\\nanchas en los N\\\\'ucleos Activos de Galaxias. La comparaci\\\\'on entre las lineas de\\nbaja- y alta ionizaci\\\\'on, sugiere que la emisi\\\\'on proviene, en parte, de una\\ngeometr\\\\'{\\\\i}a fuertemente aplanada (el disco de acreci\\\\'on?) y, en parte, de un viento\\nasociado, para una fracci\\\\'on importante de objetos radio callados que incluye a los\\nnucleos Seyfert 1 de lineas angostas (NLSy1). Sin embargo, es incierto si estos\\nresultados pueden extenderse a todos los Nucleos Activos radio callados y, sobre todo,\\na los radio fuertes.}\\n\\n\\n%% This command is so LaTeX won't stop on errors. I've put it in so\\n%% you will still be able to compile the file even if you have lost\\n%% the associated PS files of the figures.\\n\\\\nonstopmode\\n\\\\def\\\\habc{{\\\\sc{H}}$\\\\alpha_{\\\\rm BC}$\\\\/}\\n\\\\def\\\\hbnc{{\\\\sc{H}}$\\\\beta_{\\\\rm NC}$\\\\/}\\n\\\\def\\\\lya{{\\\\sc L}{\\\\rm y}$\\\\alpha$\\\\/}\\n\\\\def\\\\fevii{{\\\\sc{Fe vii}}$\\\\lambda$6087\\\\/}\\n\\\\def\\\\ovi{{\\\\sc{Ovi}}$\\\\lambda$1034\\\\/}\\n\\\\def\\\\mgii{{\\\\rm Mg\\\\sc{ii}}$\\\\lambda$2800\\\\/}\\n\\\\def\\\\niv{{\\\\sc{Niv]}}$\\\\lambda$1486\\\\/}\\n\\\\def\\\\ciii{{\\\\sc{Ciii}]}$\\\\lambda$1909\\\\/}\\n\\\\def\\\\oiiiopt{{\\\\sc{[Oiii]}}$\\\\lambda$4959,5007\\\\/}\\n\\\\def\\\\o4363{{\\\\sc{[Oiii]}}$\\\\lambda$4363\\\\/}\\n\\\\def\\\\oiiiuv{{\\\\sc{Oiii]}}$\\\\lambda$1663\\\\/}\\n\\\\def\\\\heiiuv{{\\\\rm He\\\\sc{ii}}$\\\\lambda$1640}\\n\\\\def\\\\heiiuvnc{He{\\\\sc{ii}}$\\\\lambda$1640$_{\\\\rm NC}$\\\\/}\\n\\\\def\\\\feiiuv{\\\\rm Fe{\\\\sc ii}$_{\\\\rm UV}$\\\\/}\\n\\\\def\\\\fei{\\\\rm Fe{\\\\sc i}}\\n\\\\def\\\\feii{\\\\rm Fe{\\\\sc ii}}\\n\\\\def\\\\feiii{\\\\rm Fe{\\\\sc iii}}\\n\\\\def\\\\feiiopt{\\\\rm Fe{\\\\sc ii}$_{\\\\rm opt}$\\\\/}\\n\\\\def\\\\feiiq{\\\\rm Fe{\\\\sc ii }$\\\\lambda$4570\\\\/}\\n\\\\def\\\\heiiopt{\\\\rm He{\\\\sc{ii}$\\\\lambda$4686}\\\\/}\\n\\\\def\\\\heii{He{\\\\sc{ii}}$\\\\lambda$4686\\\\/}\\n\\\\def\\\\oiii{{\\\\sc [Oiii]}$\\\\lambda\\\\lambda$4959,5007}\\n\\\\def\\\\oii{{\\\\sc [Oii]}$\\\\lambda$3727}\\n\\\\def\\\\oiir{{\\\\sc Oi}$\\\\lambda$8442}\\n\\\\def\\\\aliii{Al{\\\\sc iii}$\\\\lambda$1860}\\n\\\\def\\\\siiii{Si{\\\\sc iii]}$\\\\lambda$1892}\\n\\\\def\\\\iron{{[Fe/H]\\\\/}}\\n\\\\def\\\\ironsol{{ [Fe/H]}$_{\\\\odot}$\\\\/}\\n\\\\def\\\\feka{Fe~{\\\\sc K$\\\\alpha$\\\\/}}\\n\\\\def\\\\apj{{\\\\it Ap. J.}}\\n\\\\def\\\\aap{{\\\\it Astr. Astroph.}}\\n\\\\def\\\\apjs{{\\\\em Ap. J. Suppl.}}\\n\\\\def\\\\nat{{\\\\it Nature}}\\n\\\\def\\\\b{$\\\\beta$}\\n\\\\def\\\\kms{km~s$^{-1}$}\\n\\\\def\\\\l{$\\\\lambda$}\\n\\\\def\\\\araa{{\\\\it Annu. Rev. Astron. Astrophys. }}\\n\\\\def\\\\aj{{\\\\it Astron. J. }}\\n\\\\def\\\\mnras{{\\\\it MNRAS}}\\n\\\\def\\\\aap{{\\\\it Astron. Astrophys.}}\\n\\\\def\\\\apjl{{\\\\it Ap. J. Lett. }}\\n\\\\def\\\\aaps{{\\\\it Astron. Astrophys. Suppl. }}\\n\\\\def\\\\REF{\\\\par\\\\noindent\\\\hangindent 20pt}\\n\\\\def\\\\ab{{\\\\sc Z}}\\n\\\\def\\\\absol{{\\\\sc Z$_{\\\\odot}$\\\\/}}\\n\\\\def\\\\msol{$\\\\rm M_\\\\odot$}\\n\\\\def\\\\msoly{$ M_\\\\odot~yr^{-1}$}\\n\\\\def\\\\ltsima{$\\\\; \\\\buildrel < \\\\over \\\\sim \\\\;$}\\n\\\\def\\\\simlt{\\\\lower.5ex\\\\hbox{\\\\ltsima}}\\n\\\\def\\\\gtsima{$\\\\; \\\\buildrel > \\\\over \\\\sim \\\\;$}\\n\\\\def\\\\rfe{R$_{\\\\rm FeII}$}\\n\\\\def\\\\ai{A.I.($\\\\frac{1}{4}$)\\\\/}\\n\\\\def\\\\aox{$\\\\alpha_{ox}$\\\\/}\\n\\\\def\\\\gs{$\\\\Gamma_{\\\\rm soft}$}\\n\\\\def\\\\gh{$\\\\Gamma_{\\\\rm hard}$}\\n\\\\def\\\\G{$\\\\Gamma$}\\n\\\\def\\\\ne{n$_{\\\\rm e}$\\\\/}\\n\\\\def\\\\ergss{ergs s$^{-1}$}\\n\\\\def\\\\simgt{\\\\lower.5ex\\\\hbox{\\\\gtsima}} % > over MMM\\n\\\\def\\\\bv{{\\\\bf $\\\\bigvee$}\\\\/}\\n\\\\def\\\\qu{{$\\\\lambda$ 1400}}\\n\\\\def\\\\h{$h^{-1}$}\\n\\\\def\\\\hii{{\\\\sc Hii\\\\/}}\\n\\\\def\\\\hi{{\\\\sc Hi\\\\/}}\\n\\\\def\\\\a{$\\\\alpha$}\\n\\\\def\\\\ha{{\\\\sc H}$\\\\alpha$}\\n\\\\def\\\\nv{{\\\\sc Nv}$\\\\lambda$1240}\\n\\\\def\\\\civ{{\\\\sc{Civ}}$\\\\lambda$1549\\\\/}\\n\\\\def\\\\civnc{{\\\\sc{Civ}}$\\\\lambda$1549$_{\\\\rm NC}$\\\\/}\\n\\\\def\\\\civbc{{\\\\sc{Civ}}$\\\\lambda$1549$_{\\\\rm BC}$\\\\/}\\n\\\\def\\\\cmsq{cm$^{-2}$\\\\/}\\n\\\\def\\\\cm3{cm$^{-3}$\\\\/}\\n\\\\def\\\\md{$\\\\dot{\\\\rm M}$}\\n\\\\def\\\\rg{$\\\\rm R_{\\\\rm g}$}\\n\\\\def\\\\hb{{\\\\sc{H}}$\\\\beta$\\\\/}\\n\\\\def\\\\hg{{\\\\sc{H}}$\\\\gamma$\\\\/}\\n\\\\def\\\\hbbc{{\\\\sc{H}}$\\\\beta_{\\\\rm BC}$\\\\/}\\n\\\\begin{document}\\n\\\\maketitle\\n\\\\section{Introduction \\\\label{sec:intro}}\\n\\nThe Broad Line Region (BLR) in Active Galactic Nuclei (AGN) is unresolved with present\\nday imaging detectors and it will remain so for the foreseeable future. This is why\\n``one quasar spectrum is really worth a thousand images'' as stressed by Gary Ferland\\nat this meeting. In response we would add that {\\\\em a thousand spectra are better than\\none average spectrum}. Understanding the diversity in optical spectroscopic properties\\nof AGN is the key to any realistic AGN modeling \\\\cite{bg92,smd}. The ideal to\\nreconstruct the BLR velocity field from a single profile is not realistic \\\\cite{pen90}.\\n\\nDetermination of BLR structure and kinematics can be approached in two ways. It has\\nbeen recognized for a long time that strong broad and narrow emission lines coming from\\nboth high and low ionization species are present in Seyfert galaxies and quasars. This\\nis considered a defining spectroscopic property of AGN. Restricting attention to broad\\nlines: a) typical (i.e., strongest and most frequently observed) high ionization lines\\n(HIL: ionization potential $\\\\simgt$ 50 eV) are \\\\civ\\\\ \\\\heii\\\\ and \\\\heiiuv\\\\ lines; while\\nb) observed low ionization lines (LIL: ionization potential $\\\\simlt $ 20 eV) include\\n\\\\hi\\\\ Balmer lines, \\\\feii\\\\ multiplets, \\\\mgii, and the Ca{\\\\sc ii}\\\\ IR triplet.\\n\\nThe first approach involves the study of line variability in response to continuum\\nchanges. This approach has been pursued through a number of successful monitoring\\ncampaigns using Reverberation Mapping (RM) techniques. RM requires a large amount of\\ntelescope time and, consequently, has been achieved only for a handful of sources. RM\\nconfirms that photoionization is the main heating process in the BLR and that a large\\npart of the BLR is optically thick to the ionizing continuum (e. g. \\\\pcite{baldwin97}).\\nRM studies have quantified a main difference between HIL and LIL; HIL respond to\\ncontinuum changes with a time delay of a few days while the LIL respond with a delay of\\ntens of days. This implies that the LIL are emitted at larger distance from the\\ncontinuum source (\\\\pcite{ulr,kor95}. An exhaustive list of reference can be found in\\n\\\\pcite{smd}). RM applied to line profiles suffers from uncertainty in our knowledge\\nabout the physics of continuum and broad line formation, so that conflicting models can\\nstill describe the same lag times \\\\cite{pen91,wanpet96}.\\n\\nThe second approach involves statistical analysis of large samples of line profiles\\nwhich differ because of properties that may affect the BLR structure, for example\\nsamples of radio quiet (RQ) and radio loud (RL) AGN. Statistical studies can be done\\nfor a single line or by comparing lines sensible to different physical parameters (e.g.,\\nstrongest LIL and HIL). The statistical approach, on which we will focus here, is more\\nempirical and therefore requires a conceptual framework for interpretation. This\\napproach is often criticized as relying on several assumptions including that the\\nprofile variability does not influence profile shapes and that the non-simultaneity of\\nthe observations of LIL and HIL are unimportant. Actually as the size of high quality\\ndata samples grow these effects become less and less important.\\n\\n\\\\section{Baring the Broad Profiles \\\\label{bare}}\\n\\nThe collection of moderate resolution (\\\\l/$\\\\Delta$\\\\l $\\\\sim 10^3$) optical and UV\\nspectra of good quality (S/N $\\\\simgt$ 20 in the continuum) has become possible only in\\nrecent years thanks to the widespread use of CCD detectors and the unprecedented\\nsensitivity and resolution of the UV spectrographs on board HST. For practical\\npurposes, \\\\hi\\\\ \\\\hb\\\\ and \\\\civ can be considered representative of HIL and LIL\\nrespectively. They are also the best lines for statistical studies because they permit\\ncomparison in the same sources out to z=1.0. The linearity of response of the\\ncurrently employed detectors has made possible a reliable correction for emission\\nfeatures contaminating \\\\hb\\\\ and \\\\civ, which are: (1) \\\\feii\\\\ emission; significant\\n\\\\feiiuv\\\\ emission contaminates the red wing of \\\\civ, and has been identified in I Zw 1\\nby \\\\pcite{m96} and later confirmed by \\\\pcite{lao97}; (2) \\\\heii\\\\ emission for \\\\hb, and\\n\\\\heiiuv\\\\ + \\\\oiiiuv\\\\ for \\\\civ; (3) \\\\oiii\\\\ for \\\\hb; (4) narrow component, present in\\nseveral cases in both \\\\hb\\\\ and \\\\civ.\\n\\n\\n\\\\civ\\\\ often shows a narrow core with FWHM $\\\\sim$ 1000-2000 \\\\kms, which is\\nsystematically broader than the narrow component of \\\\hb\\\\ (\\\\hbnc). The separation\\nbetween the broad component \\\\civbc\\\\ and the core component is often ambiguous. This\\ncore however shows no shift with respect to the AGN rest frame \\\\cite{brot94}, no\\nvariations \\\\cite{turla}, and correlates with \\\\oiii\\\\ prominence \\\\cite{franc92}. It can\\ntherefore be ascribed to the NLR and considered as the narrow line component of \\\\civ\\\\\\n(\\\\civnc). The different width between \\\\civnc\\\\ and \\\\hbbc\\\\ can be understood in terms of\\ndensity stratification \\\\cite{sm99} without invoking an additional emitting region such\\nas the so-called ``intermediate line region''. Even if \\\\civnc\\\\ fractional intensity is\\nsmall ($\\\\sim$ 10\\\\%), and in some cases obviously absent, failure to account for \\\\civnc\\\\\\nhas led to the erroneous conclusions that FWHM \\\\civbc\\\\ $>$ FWHM \\\\hbbc\\\\ and that the\\n\\\\civ\\\\ peak shows no shift with respect to \\\\hb\\\\ \\\\cite{cb96}.\\n\\n\\\\section{A DIFFERENT BLR STRUCTURE IN RADIO LOUD AND RADIO QUIET AGN? \\\\label{struct}}\\n\\n\\\\scite{m96} made a comparison between \\\\civbc\\\\ and \\\\hbbc\\\\ for a sample of 52 AGN (31\\nRL). They presented measures of radial velocity for the blue and red sides of \\\\hbbc\\\\\\nand \\\\civbc\\\\ at 5 different values of fractional intensity which provide a quantitative\\ndescription of the profiles. The reference frame was set by the measured velocity of\\n\\\\oiii$\\\\lambda$5007$\\\\rm{\\\\AA}$ (IZw1 was the only exception). Standard profile parameters\\nlike peak shift, FWHM, asymmetry index and curtosis can be extracted from these\\nmeasures. Representative profiles constructed from the {\\\\em median values} of \\\\civbc\\\\\\nand \\\\hbbc\\\\ $v_r$\\\\ are reproduced in the left panels of Fig. \\\\ref{fig:rq} and\\n\\\\ref{fig:rl} for the radio quiet (RQ) and radio loud (RL) samples respectively.\\n\\\\begin{figure}\\n %\\\\begin{center}\\n \\\\leavevmode\\n \\\\includegraphics[width=\\\\columnwidth, height=8cm]{fig01.eps}\\n% \\\\includegraphics[width=\\\\textwidth, height=10cm]{Fig01dd.eps}\\n\\\\caption[]{Profiles of \\\\civbc\\\\ (solid lines) and \\\\hbbc\\\\ normalized to the same peak\\nintensity and constructed from median values of the radial velocities measured on the\\nblue and red sides of the profiles for the 21 RQ AGN of \\\\scite{m96} (left panel).\\nEmission line profiles of \\\\civ\\\\ (middle panel) and \\\\hb\\\\ (right panel) of the prototype\\nNLSy1 galaxy I Zw 1, adapted from \\\\scite{m96}. The thick and the dotted lines trace \\\\hb\\\\\\nand \\\\oiii\\\\ after \\\\feiiopt\\\\ (dashed line) subtraction. \\\\label{fig:rq}}\\n %\\\\end{center}\\n\\\\end{figure}\\n\\n\\\\civbc\\\\ is broader than \\\\hbbc in both RQ and RL samples and it is {\\\\em almost always}\\nblueshifted relative to \\\\hbbc. However Fig. \\\\ref{fig:rq} and Fig. \\\\ref{fig:rl} show\\nsignificant differences between RQ and RL AGN. In RQ AGN, \\\\civbc\\\\ is significantly\\nblueshifted with respect to the source rest frame while \\\\hbbc\\\\ is symmetric and\\nunshifted. Contrarily in RL AGN \\\\civbc\\\\ is more symmetric, while \\\\hbbc\\\\ is shifted to\\nthe red at peak intensity and redward asymmetric as well (the median profile\\ncorresponds to the type AR,R according to \\\\pcite{sul89}). There are two important\\nresults which are not displayed in the Figures: (i) in RQ AGN, \\\\civbc\\\\ blueshifts are\\napparently uncorrelated with respect to any \\\\hbbc\\\\ line profile parameter and the\\nlargest \\\\civ\\\\ blueshifts are associated with the lowest W(\\\\civ); (ii) in RL AGN, on the\\ncontrary, \\\\civbc\\\\ and \\\\hbbc\\\\ line profile parameters (FWHM and peak shift) appear to be\\ncorrelated. Asymmetry index of \\\\civbc\\\\ and \\\\hbbc, even if not correlated, shows a clear\\ntrend toward asymmetries of the same kind (symmetric or redward asymmetric). These\\nfindings on \\\\civbc\\\\ have been confirmed by other authors (\\\\pcite{wills95}, save the\\ndifference in terminology and line profile decomposition) and especially by an analysis\\nof archival HST/FOS observations which have become publicly available after 1995\\n\\\\cite{sul20}.\\n\\nThe LIL and HIL emitting regions are apparently de-coupled in at least some RQ\\nsources. The ``de-coupling'' is well seen in I Zw 1, the prototype Narrow Line Seyfert\\n1 Galaxy (NLSy1; see Fig. \\\\ref{fig:rq}). The \\\\hb\\\\ profile is very narrow, slightly\\nblueward asymmetric and unshifted with respect to the rest frame defined by 21 cm\\nobservations, while the \\\\civ\\\\ profile is almost totally blueshifted. At least in the\\ncase of I Zw 1 the distinction between LIL and HIL emitting regions appears to be\\nobservationally established (it was actually suggested because of the difficulty to\\nexplain the relative strengths of LIL and HIL emission using a photoionized ``single\\ncloud;'' \\\\pcite{cs88}). There is a very important zeroth-order result here: since I Zw\\n1 is a strong \\\\feiiuv\\\\ emitter, we have HIL \\\\civ\\\\ and LIL \\\\feiiuv\\\\ in the same\\nrest-frame wavelength range. We see that \\\\feiiuv\\\\ is obviously unshifted (this can be\\nvery well seen by shifting an \\\\feiiuv\\\\ template to the peak radial velocity of \\\\civ).\\nThis result disproves models that see an (unknown) wavelength dependent mechanism\\naccounting for the quasar broad line shifts relative to the quasar rest frame.\\n\\nRL AGN apparently mirror RQ AGN in a curious way: \\\\civbc\\\\ is more symmetric, while\\n\\\\hbbc\\\\ shows preferentially redshifted profiles and increasingly redward asymmetries.\\nLarge peak redshifts ($v_r \\\\simgt 1000$ \\\\kms, as in the case of OQ 208, Fig.\\n\\\\ref{fig:rl}) are rarely observed; \\\\hbbc\\\\ peak shifts are usually small ($\\\\Delta\\nv_r$/FWHM $\\\\ll$ 1, median profile of Fig. \\\\ref{fig:rl}). RL \\\\civbc\\\\ and \\\\hbbc\\\\ data\\nleave open the possibility that both lines are emitted in the same region. \\\\civbc\\\\\\nshows a red-wing (very evident in the latest, higher S/N spectra analyzed by\\n\\\\scite{sul20}), which cannot be entirely accounted for by \\\\feiiuv emission. It is\\ninteresting to note that superluminal sources with apparent radial velocity $\\\\beta_{\\\\rm\\napp} \\\\sim 5-10$~ (whose radio axis is probably oriented close to the line of sight in\\nthe sample of \\\\scite{m96} show very strong \\\\civ\\\\ redward asymmetries, low W(\\\\civ) and\\nW(\\\\hbbc). This result suggests that redshifts are maximized in RL objects at\\n``face-on'' orientation (we assume that any disk is perpendicular to the radio axis).\\n\\n\\\\section{NLSy1 NUCLEI ARE NOT A DISJOINT RQ POPULATION}\\n\\nNLSy1 are neither peculiar nor rare. The 8$^{th}$\\\\ edition of the \\\\scite{veron98}\\ncatalogue includes 119 NLSy1 satisfying the defining criterion FWHM Balmer $\\\\simlt$\\n2000 \\\\kms. They account for $\\\\approx 10$\\\\%\\\\ of all AGN in the same redshift and\\nabsolute magnitude range. Attention toward NLSy1 remained dormant after their\\nidentification as a particular class \\\\cite{op85} until it was discovered that they may\\nrepresent $\\\\approx$1/3--1/2 of all soft X-ray selected Seyfert 1 sources (e. g.,\\n\\\\pcite{grupe98}). NLSy1 are also apparently favored in AGN samples selected on the\\nbasis of color. They account for 27\\\\%\\\\ of the RQ \\\\scite{bg92} sample, probably because\\nof an optical continuum that is steeply rising toward the near UV. NLSy1 do not occupy\\na disjoint region in parameter space. They are at an extremum in the FWHM(\\\\hb) vs.\\n\\\\rfe\\\\ (=I(\\\\feii \\\\l 4570/I(\\\\hbbc)) and in the ``Eigenvector 1'' parameter spaces\\n\\\\cite{bg92,bf99,smd}. Also, the soft X-ray spectral index \\\\gs\\\\ shows a continuous\\ndistribution which includes NLSy1 at the high end \\\\cite{wang96,smd,sul20}.\\n\\n\\\\begin{figure}\\n %\\\\begin{center}\\n \\\\leavevmode\\n \\\\includegraphics[width=\\\\columnwidth, height=8cm]{fig02.eps}\\n% \\\\includegraphics[width=\\\\textwidth, height=10cm]{Fig01dd.eps}\\n \\\\caption[]{Left panel: Profiles of \\\\civbc\\\\ (solid lines) and \\\\hbbc\\\\ normalized to the same\\n peak intensity and constructed from median values of the radial velocities measured on\\n the blue and red sides of the profiles for the 31 RL AGN of \\\\scite{m96}.\\n Middle panel: \\\\hb\\\\ spectrum of OQ 208, showing a single, widely displaced \\\\hbbc\\\\ peak (adapted from \\\\pcite{m93}).\\n Right panel: \\\\ha\\\\ profile of the prototype of ``wide-separation double peakers'' Arp 102B.\\n Unpublished spectrum obtained at the 1.82 m telescope of the Asiago observatory on March 25, 1989.\\n The thick solid line traces \\\\hbbc.}\\n \\\\label{fig:rl}\\n %\\\\end{center}\\n\\\\end{figure}\\n\\nOrientation can easily explain much of the RQ phenomenology observed by \\\\scite{m96}. I\\nZw 1 can be considered as an extremum with an accretion disk seen face-on\\n(i$=0^\\\\circ$), and an outflowing wind observed along the disk axis. We can infer that\\nthe opening angle of any \\\\civ\\\\ outflow is probably large (i. e., the wind is quasi\\nspherical) because \\\\civ\\\\ profiles like I Zw 1 are rare. Other NLSy1 show low W(\\\\civ),\\nand strong \\\\feiiopt, but do not always show large \\\\civ\\\\ blueshifts \\\\cite{rp97}.\\nNonetheless, it is still possible that NLSy1 may be structurally different from other\\nRQ AGN. If the soft X-ray excess of NLSy1 is due to high accretion rate, then a slim\\naccretion disk is expected to form \\\\cite{abram88}. Line correlations presented in\\n\\\\cite{sul20} appear to hold until FWHM(\\\\hb)$\\\\simlt$ 4000 \\\\kms. For FWHM$\\\\simgt$ 4000\\n\\\\kms line parameters appear to be uncorrelated however it is still unclear it is at\\npresent unclear because of the difficulty in measuring weak and broad \\\\feiiopt sources\\nand/or because of a BLR structural difference. This limit may be related to the\\npossibility of sustaining a particular disk structure and an HIL outflow. A second\\nparameter, independent from orientation is needed to account for the FWHM(\\\\hbbc) vs\\n\\\\rfe\\\\ vs \\\\gs\\\\ sequences (see \\\\pcite{smd,sul20} for a detailed discussion).\\n\\n\\n\\\\section{Inferences on BLR Models for RQ AGN}\\n\\nModels developed almost independently of the data through the 80's and early 90's.\\nThe situation has now changed because of three main developments: (1) the ``Eigenvector\\n1'' correlations allow a systematic view of the change in optical emission line\\nproperties for different classes of AGN \\\\cite{bg92,bf99,smd}; (2) the \\\\civ\\\\ - \\\\hb\\\\\\ncomparison has yielded direct clues about the structure of the BLR \\\\cite{m96,sul20} and\\n(3) data collected for RM projects provide a high-sampling description of line\\nvariations. For instance, binary black hole scenarios \\\\cite{gask96} were recently\\nchallenged by the failure to detect the radial velocity variations expected from\\nprevious observations and model predictions \\\\cite{eracl97}.\\n\\nA model in which \\\\civ\\\\ is emitted by outflowing gas (e.g. a spherical wind) while\\n\\\\hbbc\\\\ is emitted in a flattened distribution of gas (observed in a direction that\\nminimizes velocity dispersion) such as an optically thick disk (obscuring the receding\\nhalf of the \\\\civ\\\\ flow, \\\\pcite{liv97}) or at the wind base is immediately consistent\\nwith the I Zw 1 data. The big question is whether the results for I Zw 1 can be\\nstraightforwardly extended to other RQ AGN.\\n\\nAn accretion disk (AD) provides a high density and high column density medium for\\n\\\\feii\\\\ production (e. g. \\\\pcite{dj92}), and possibly other low ionization lines such as\\nCaII (e. g. \\\\pcite{dd99}). AD avoid conflict with the stringent restrictions on line\\nprofile smoothness imposed by the first extremely high s/n Balmer line observations\\n(\\\\pcite{arav97,arav98}) of -incidentally- two NLSy1. They place a lower limit of\\n(10$^{7-8}$) on the number of discrete emitters needed to explain the observed profiles.\\n\\nWinds arise as a natural component of an AD model when the effects of radiative\\nacceleration are properly taken into account \\\\cite{murray95,mc98} or when a\\nhydromagnetic or hydrodynamic treatment is performed \\\\cite{bottorff97,williams99}. A\\nsignature of radiative acceleration is provided by observations of ``double troughs'' in\\n$\\\\approx \\\\frac{1}{5}$ of BAL QSOs i. e., of a hump in the absorption profiles of \\\\nv\\\\\\nand \\\\civ\\\\ at the radial velocity difference between \\\\lya\\\\ and \\\\nv, 5900 \\\\kms. Such a\\nfeature indicates that \\\\lya\\\\ photons are accelerating the BAL clouds (\\\\pcite{arav94},\\nand references therein). Additional evidence is provided by the radial velocity\\nseparation in the narrow absortion components of \\\\lya\\\\ and \\\\nv\\\\ which show the same\\n$\\\\Delta v_r$\\\\ of the two doublet components of \\\\civ\\\\ (e. g. \\\\pcite{wampler91}).\\n\\n\\\\section{The Trouble With Bare Accretion Disks and Bipolar Flows}\\n\\nRelativistic Keplerian disks \\\\cite{ch89,sb93} may explain unusual profile shapes (e.g.\\ndouble-peaked profiles of Balmer emission lines; \\\\pcite{eh94,sul95}). Uniform\\naxisymmetric disk models produce double-peaked line profiles with the blue peak\\nstronger than the red peak because of Doppler boosting, a feature that is not always\\nobserved in these already rare profiles. To solve this problem, \\\\scite{sb95} and\\n\\\\scite{eracl95}, proposed that the lines can originate in an eccentric (i.e.\\nelliptical) disk. Simple disk illumination models can also produce single peaked LIL,\\nprovided they are produced at large radii ($\\\\simgt 10^3$\\\\ gravitational radii) or that\\nthe disk is observed at small inclination \\\\cite{dc90,rokaki92,sul98}. The first of these\\nconditions may be met in all NLSy1 galaxies; both of them seem to be met in I Zw 1.\\n\\nAside from NLSy1 sources, there is general disagreement between observations and model\\npredictions for externally illuminated Keplerian disks in a line shift-- asymmetry\\nparameter space \\\\cite{sul90}. Only a minority ($\\\\simlt$ 10 \\\\%) of RL and a handful of\\nRQ AGN show double peaked Balmer lines suggestive of a Keplerian velocity field\\n\\\\cite{eh94,sul99}. Double-peakers (e. g. Arp 102B in Fig. \\\\ref{fig:rl},\\nFWHM(\\\\hbbc)$\\\\simgt$10000 \\\\kms) cannot be like the classical cases because the line\\nwidths are much smaller. The peaks often vary out of phase (Arp 102B: \\\\pcite{mp90}, 3C\\n390.3: \\\\pcite{zheng91}). Double peaks (NGC 1097) \\\\cite{sb93,sb95} or one of the peaks\\n(Pictor A) \\\\cite{sul95} sometimes appear quite suddenly. Profile variability studies of\\nBalmer lines force us to introduce second order modifications to the basic scheme, such\\nas: eccentric rings and precession \\\\cite{eracl95,sb97}, inhomogeneities such as\\norbiting hot spots \\\\cite{zheng91}, and warps \\\\cite{bachev99}. Not even these {\\\\em\\nepicycles} are always capable of explaining the observed variability patterns. Even if\\nelliptical AD models do well in explaining the integrated profiles, they face important\\ndifficulties in explaining variability patterns.\\n\\nA serious problem for AD models of emission lines is emerging from spectropolarimetric\\nobservations. If profile broad line shapes are orientation dependent then, in\\nprinciple, the profile shape in polarized light will depend on the distribution of the\\nscatterers relative to the principal axis and to our line of sight. Early\\nspectropolarimetric results showed a discrepancy with the simple disk +\\nelectron-scattering-dominated atmosphere models, which predicted polarization\\nperpendicular to the radio axis. The observed polarization is low, parallel to the disk\\naxis, and shows no statistically significant wavelength dependence \\\\cite{anton88}.\\nRecently \\\\scite{anton96} and \\\\scite{corbett98} included double-peakers in their\\nsamples, and obtained troublesome results for disk emission models because the\\npolarized \\\\ha\\\\ profiles are centrally peaked \\\\cite{corbett98}. They investigated the\\ncase of disk emission where the scattering particles are located above and below an\\nobscuring torus, along its poles. This ``polar scattering model'' is successful in\\nexplaining the polarized profiles {\\\\em but not the position angle of the polarization\\nvector}.\\n\\nThe same polarization studies indicate that the {\\\\em only} scenario that can account\\nfor both the shapes of the scattered line profiles and the alignment of the optical\\npolarization with the radio jet in wide separation double peakers like Arp 102B (Fig.\\n\\\\ref{fig:rl}) involves a {\\\\em biconical} BLR within an obscuring torus. \\\\ha\\\\ photons\\nemitted by clouds participating in a biconical flow are scattered towards the observer\\nby dust or electrons in the inner wall of the surrounding torus. The particular case of\\nbiconical outflow was first developed to reproduce observed profiles by\\n\\\\scite{zheng90}. This model has been successfully applied to fit observed profiles in\\ndouble-peaked objects \\\\cite{zheng91,sul95}.\\n\\nDouble peaked or single blueshifted peak LIL profiles fitted with bi-cone outflow\\nmodels require that the receding part of the flow is also seen. Self-gravity may be\\nimportant beyond $\\\\sim 1$ pc, and the disk may be advection-dominated and optically\\nthin \\\\cite{liv96}. Recent work by \\\\scite{sh99} models the vertical structure of AD and\\nthe origin of thermal winds above AD. They not only find that a wind powered by a\\nthermal instability develops in all disks with certain opacity laws but also that in\\ndisks dominated by bremsstrahlung radiation, a time-dependent inner hole develops below\\na critical accretion rate. This scenario provides a natural explanation for transient\\ndouble-peakers, such as NGC1097 \\\\cite{sb95,sb97}, but low accretion rate is a\\nrequirement for {\\\\em both} advection dominated disks and hole formation.\\n\\n\\\\scite{sul95} explored the idea that the double-peaked emitters represent a\\ngeometrical extremum where an outflow is viewed close to pole-on. However,\\ndouble-peakers are associated with double-lobe radio-sources suggesting that the line\\nof sight has a considerable inclination to the axis of the jets. The problem arises\\n{\\\\em only} if the core (pc scale) jets is related to the much larger (100 kpc scale)\\njets. There is both theoretical (e. g. \\\\pcite{valtonen99}) and observational evidence\\nagainst this assumption.\\n\\n\\\\section{Emission from Clouds Illuminated by an Anisotropic Continuum}\\n\\nModels based on radiative acceleration of optically thick clouds with small volume\\nfilling factor gained wide acceptance in the Eighties (\\\\pcite{om86} and references\\ntherein; see also \\\\pcite{binette96}). However, problems with cloud confinements and\\nstability \\\\cite{mathews90} have made them increasingly less frequently invoked to\\nexplain observations.\\n\\nFirst RM studies on Balmer lines excluded radial, and favored orbital or chaotic\\nmotions (e.g. \\\\pcite{kg91,kor95}). \\\\scite{goadw96} applied RM techniques to one of the\\nmost extensively monitored objects: NGC 5548. They ruled out radial motions, and found\\nthat the \\\\civ\\\\ line variations are broadly consistent with a spherical BLR geometry, in\\nwhich clouds following randomly inclined circularly Keplerian orbits are illuminated by\\nan anisotropic source of ionizing continuum. A RM result favoring Keplerian motion may\\nbe approximately correct also for models in which the emitting gas is not bound, such\\nas a wind, since most of the emission occurs near the base of the flow, when the\\nvelocity is still close to the escape velocity which is similar to the Keplerian\\nvelocity \\\\cite{mc98}.\\n\\n\\\\section{Is the disk + wind model applicable to all AGN?}\\n\\nEmission from a terminal flow can explain the recent observations of Goad et al. 1999\\nwho reported that LIL (\\\\mgii + \\\\feiiuv) in NGC 3516 do not respond to continuum\\nvariations which did induce detectable variability in the HIL (\\\\lya\\\\ and \\\\civ) lines.\\nHydromagnetic wind models such as those developed by \\\\scite{emmering92} and\\n\\\\scite{bottorff97} exhibit these basic properties. A two-zone wind provides another\\nscenario for the different origins of LIL and HIL.\\n\\nTurning to the general population of RL AGN, the predominance of redshifts and redward\\nasymmetric profiles is difficult to explain. Several lines of evidence suggest a\\nsignificant role of gravitational redshift in RL AGN \\\\cite{corbin97} possibly related\\nto a lower distance (in units of gravitational radii) between BLR and central black\\nhole, which may be systematically more massive in RL than in RQ AGN. If this is the\\ncase, then a double zone wind may be present also in RL AGN, since \\\\civbc\\\\ is still\\nsystematically blueshifted with respect to \\\\hbbc. The ``correlation'' between \\\\civbc\\\\\\nand \\\\hbbc\\\\ parameters could be due to the impossibility of maintaining a radial flow\\nalong the disk axis, where a relativistic jet is instead propagating. This will make\\nany HIL outflow possible only at lower latitudes over the disk plane, and therefore\\nwill produce more similar \\\\hbbc\\\\ and \\\\civbc\\\\ profiles.\\n\\n\\n\\\\section{CONCLUSION}\\n\\nWhile observations support emission from an accretion disk and an associated spherical\\nwind in RQ AGN with FWHM(\\\\hbbc) $\\\\simlt$ 4000 \\\\kms, there is not enough observational\\nsupport to warrant the same conclusion for RL AGN (and possibly RQ with FWHM$>$4000\\n\\\\kms), although a disk + wind model is a viable possibility also in this case. Wide\\nseparation double peakers (mostly RL) do not provide conclusive evidence in favor of\\nLIL disk emission; rather, there is evidence against disk emission as well as against\\nevery other reasonably simple scenario.\\n\\n\\\\acknowledgements DD-H acknowledges support through grant IN109698 from PAPIIT-UNAM. PM\\nacknowledges financial support from MURST through grant Cofin 98-02-32, as well as\\nhospitality and support from IA-UNAM. We also acknowledge consistent (cycles5-9 AR and\\nGO) rejection of proposals to continue this work.\\n\\n%There are conflicting lines of evidences. It is unclear whether\\n%wide separation double-peaks in Balmer lines are due to rotation\\n%or to outflow. Their rarity and abnormal line width suggest that\\n%they may be a peculiar class in a short-lived phase of their\\n%evolution.\\n%% When using the rmaacite package, the \\\\bibitem command should be of\\n%% the format:\\n%%\\n%% \\\\bibitem[AUTHOR<YEAR>]{KEY}\\n%%\\n%% so that the \\\\cite{KEY}, etc. commands will work properly.\\n%%\\n%% If you are doing the citations manually, then you can just use\\n%% `\\\\bibitem{}' instead. 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J. 1991, \\\\apj, 368, 40\\n\\\\bibitem[Wang et al.<1996>]{wang96} Wang T., Brinkmann W., Bergeron J. 1996, \\\\aap, 309, 81\\n%\\\\bibitem[Wandel et al.<1999>]{wandel99} Wandel A, Peterson BM, Malkan MA. 1999. \\\\apj 526:579-91\\n%\\\\bibitem[Wanders et al.<1995>]{wanders95} Wanders,\\n\\\\bibitem[Wanders \\\\& Peterson<1996>]{wanpet96} Wanders I., Peterson B. M. 1996, \\\\apj, 466, 174\\n\\\\bibitem[Williams et al.<1999>]{williams99} Williams RJR, Baker AC, Perry JJ. 1999. {\\\\it MNRAS}, in press\\n\\\\bibitem[Wills et al.<1995>]{wills95} Wills B. J., Thompson K. L., Han M., Netzer H., Wills D. et al. 1995, \\\\apj, 447, 139\\n\\\\bibitem[Zheng et al.<1990>]{zheng90} Zheng W., Binette L., Sulentic J. W., 1990, \\\\apj, 365, 115\\n\\\\bibitem[Zheng et al.<1991>]{zheng91} Zheng W., Veilleux S., Grandi S. A. 1991. \\\\apj, 381, 418\\n\\\\end{thebibliography}\"\n }\n]","isConversational":false}}},{"rowIdx":96,"cells":{"paper_id":{"kind":"string","value":"astro-ph0002097"},"title":{"kind":"string","value":"A phase-reference study of the quasar pair 1038+528A,B"},"authors":{"kind":"list like","value":[{"author":"Mar\\'{\\i}a J. Rioja \\inst{1} \\inst{2}"},{"author":"Richard W. Porcas\\inst{3} % \\fnmsep\\thanks{Just to show the usage % of the elements in the author field}"}],"string":"[\n {\n \"author\": \"Mar\\\\'{\\\\i}a J. Rioja \\\\inst{1} \\\\inst{2}\"\n },\n {\n \"author\": \"Richard W. Porcas\\\\inst{3} % \\\\fnmsep\\\\thanks{Just to show the usage % of the elements in the author field}\"\n }\n]","isConversational":false},"abstract":{"kind":"string","value":"We present results from $\\lambda$ 3.6~cm observations of the quasar pair \\object{1038+528} A and B, made in 1995 using the VLBA together with the Effelsberg 100m telescope. We describe the use of a phase-referencing technique to measure the astrometric separation between the quasars. We also introduce a new data analysis method - \"hybrid double mapping\" - which preserves the relative astrometric information in a single VLBI hybrid map for close source pairs. We combine our measurements with those from three previous epochs, the earliest in 1981. Our new observations confirm the evolution within the structure of quasar B, previously proposed to explain the measured change in the relative separation of the pair. Our upper bound for any systematic proper motion between the mass centres of quasars A and B is 10~$\\mu$as~yr$^{-1}$. This is set by the limited precision in defining the reference points in the quasars at different epochs and by possible instabilities of the source \"core\" locations. A separate analysis enables us to put more stringent upper limits to any core motions along the two source axes. \\keywords{Instrumentation: interferometers -- Techniques: interferometric -- Astrometry -- Radio continuum: general }"},"latex":{"kind":"list like","value":[{"name":"rioja_17jan2000.tex","string":"% aa.dem\n% AA vers. 4.01, LaTeX class for Astronomy & Astrophysics\n% demonstration file\n% (c) Springer-Verlag HD\n%-----------------------------------------------------------------------\n%\n%\\documentclass[referee]{aa} % for a referee version\n%\n\\documentclass{aa}\n%\n\\usepackage{psfig}\n\n\\begin{document}\n\n \\thesaurus{03 % A&A Section 3: Extragalactic astronomy\n (03.09.2; % Instrumentation: interferometers,\n 03.20.2; % Techniques: interferometric, \n 05.01.1; % Astrometry,\n 13.18.2)} % Radio continuum: general.\n%\n \\title{A phase-reference study of the quasar pair 1038+528A,B }\n% \\title{A phase-reference study of the}\n% \\subtitle{quasar pair 1038+528A,B }\n\n% \\subtitle{I. Overviewing the $\\kappa$-mechanism}\n\n \\author{Mar\\'{\\i}a J. Rioja \n \\inst{1}\n \\inst{2}\n \\and\n Richard W. Porcas\\inst{3}\n% \\fnmsep\\thanks{Just to show the usage\n% of the elements in the author field}\n }\n\n \\offprints{Mar\\'{\\i}a J. Rioja}\n\n \\institute{Observatorio Astron\\'omico Nacional (OAN), Apdo. 1143, \n E-28800 Alcal\\'a de Henares, Spain \\\\\n email: rioja@oan.es\n \\and\n Joint Institute for VLBI in Europe (JIVE), \n NL-7990 AA Dwingeloo, The Netherlands \\\\\n \\and\n Max-Planck Institut f\\\"ur Radioastronomie, Auf dem H\\\"ugel 69,\n D-53121 Bonn, Germany \\\\\n email: porcas@mpifr-bonn.mpg.de \n% \\thanks{The university of heaven temporarily does not\n% accept e-mails}\n }\n\n \\date{Received 5 October, 1999; accepted XX }\n\n \\titlerunning{Relative Astrometry of 1038+528AB}\n \\authorrunning{Rioja \\& Porcas}\n\n \\maketitle\n \n \\begin{abstract}\n\nWe present results from $\\lambda$ 3.6~cm observations of the quasar pair \n\\object{1038+528} A and B, made in 1995 using the VLBA together with the \nEffelsberg 100m telescope. We describe the use of a phase-referencing \ntechnique to measure the astrometric separation between the quasars.\nWe also introduce a new data analysis method - \"hybrid double mapping\" - \nwhich preserves the relative astrometric information in a single VLBI \nhybrid map for close source pairs. We combine our measurements with those \nfrom three previous epochs, the earliest in 1981. \nOur new observations confirm the evolution within the structure of quasar B, \npreviously proposed to explain the measured change in the relative separation \nof the pair. Our upper bound for any systematic proper motion between the \nmass centres of quasars A and B is 10~$\\mu$as~yr$^{-1}$. This is set by the \nlimited precision in defining the reference points in the quasars at \ndifferent epochs and by possible instabilities of the source \"core\" locations.\nA separate analysis enables us to put more stringent upper limits to any \ncore motions along the two source axes.\n\n \\keywords{Instrumentation: interferometers --\n Techniques: interferometric --\n Astrometry --\n Radio continuum: general\n }\n \\end{abstract}\n\n%\n%________________________________________________________________\n\n\\section{Introduction}\n\nThe quasar pair 1038+528~A,B (Owen et al. \\cite{owen78}) \nconsists of two\nflat-spectrum radio sources, with redshifts 0.678 and 2.296 (Owen et\nal. \\cite{owen80}), separated on the sky by only 33\\arcsec. \nThis system provides a unique opportunity to carry out high precision, relative\nastrometric studies using the full\nprecision of VLBI relative phase measurements, \nsince most sources of phase errors are common for the 2 sources\n(Marcaide \\& Shapiro \\cite{marca83}).\n\n VLBI studies of the mas-scale structure of flat-spectrum quasars\nshow that they typically have ``core-jet'' morphologies, consisting of a highly\ncompact feature (the ``core'') located at the base of an extended linear feature \nor line of lower brightness components (the ``jet'').\nBoth 1038+528 A and B exhibit such structures.\nIn standard models of extragalactic radio sources, these radio-emitting \nfeatures\narise from a collimated beam of plasma which is ejected with a highly \nrelativistic bulk velocity from a region close to a central massive object \nsuch as a black hole (see eg. Blandford \\& K\\\"onigl \\cite{blandford86}).\nWhilst jet features may correspond to shocks in the moving plasma, and \ncan give rise to the observed ``superluminal'' component motions in some \nsources (Porcas \\cite{porcas87}),\nthe ``core'' emission is thought to arise from a more-or-less permanent location close to\nthe origin of the beam, where the ambient conditions correspond to a transition\nfrom optically thick to optically thin emission at the observed frequency.\nAlthough the ``core'' position may thus be frequency-dependent, for a fixed\nobserving frequency\nthe core should provide a stable marker, anchored to the central mass of\nthe quasar, whose location can be used to define a precise position for\nthe object as a whole.\nAlthough short time-scale variations in physical conditions may cause\nsmall changes in the ``core'' location, over long time-scales it may be\nused to track any systematic proper motion of the quasar.\n\nThe results from a near decade-long VLBI monitoring program on 1038+52A,B at\n$\\lambda$ 3.6 and 13~cm (from 1981.2 to 1990.5) \nare reported by Rioja et al. (\\cite{rioja97}), whose main conclusions \ncan be summarized as follows:\n\n\\begin{enumerate}\n\n\\item There is no evidence of any relative proper motion between the \n quasars A and B. The uncertainties in the astrometric parameters \n result in an upper bound to any systematic relative \n motion between the cores of 10~$\\mu$as~yr$^{-1}$, consistent\n with zero.\n\n\\item A compact feature within the jet of quasar B, chosen as the \n reference point for the structure, expands away from the core at \n a steady, slow rate of $\\sim~18~\\pm~5~\\mu$as~yr$^{-1}$, corresponding \n to v=$(0.8~\\pm~0.2)~h^{-1}$~c for a Hubble constant,\n H$_0$ = 100~h~km~s$^{-1}$~Mpc$^{-1}$; q$_0=0.5$. These values are used \n here throughout.\n\n\\item The accuracy of the relative separation measurement is limited by \n noise and source structure, with estimated precisions of about \n $50~\\mu$as at $\\lambda$ 3.6~cm at any epoch.\n\n\\item Confirmation of the consistently large offset (about 0.7 mas) between\n the positions of the peak of brightness (``core'') at $\\lambda$ 3.6 \n and 13~cm in quasar A.\n\n\\end{enumerate}\n\nNew VLBI observations of this pair were made in November 1995 (1995.9) \nat $\\lambda$ 2, 3.6 and 13~cm. In this paper we report on results from \nour analysis of the 3.6~cm observations and investigate the temporal \nevolution of the source structures and relative separation from all \nfour epochs spanning $\\sim 15$ years. \nInvestigations of frequency-dependent source structure have also been made \nfrom a comparison of the astrometric measurements\nof the separations between A and B at all 3 wavelengths observed in 1995;\nthese will be presented elsewhere (Rioja \\& Porcas in preparation).\n\nOur new observations are described in Sect. 2. In Sect. 3 we describe\nthe data reduction and mapping techniques used, and in Sect. 4 an analysis\nof the measurements in the maps.\nIn Sect. 5 we compare the astrometric results from these observations\nwith those from previous epochs and analyse the changes in \nseparation. Conclusions are presented in Sect. 6.\n\n%__________________________________________________________________\n\n\\section{Observations}\n\nThe pair of radio sources 1038+528 A and B was observed with the\nNRAO Very Long Baseline Array (VLBA) on November 10, 1995,\nfor a total of 13 hours, alternating every 13 minutes between\nobservations in dual 3.6/13~cm mode and observations at 2~cm. The\n100m telescope at Effelsberg was also included in the array for the\n3.6/13~cm scans. The primary beamwidths of all the antennas were\nsufficiently large that both sources could be observed simultaneously\nat all wavelengths. Each 10 minute observation of 1038+52A,B was\npreceded by a 3 minute observation of the compact calibration source\n\\object{0917+624}, to monitor the behaviour of the array.\n\nAll stations used VLBA terminals to record an aggregate \nof 64 MHz bandwidth for each scan, using 1-bit sampling, subdivided into\n8 channels (mode 128-8-1). For the dual 3.6/13~cm scans, four 8-MHz channels\nwere recorded for each band (2254.5--2286.5 MHz; 8404.5--8436.5 MHz), \nusing \nRHC polarisation. At 2~cm, eight 8-MHz channels (15\\,331.5--15\\,395.5 MHz)\nwere recorded in LHC polarisation.\n\nThe correlation was made at the VLBA correlator in Socorro (New Mexico).\nAs for previous epochs, two separate ``passes'' were needed, using different \nfield centres for the two sources, to recover data\nfor both the A and B quasars from the single observation. \nOutput data sets were generated for the two sources, consisting of the\nvisibility functions averaged to 2 s, with samples every 1 MHz in frequency\nacross the bands. \n\n\\section{Data reduction} \n\nWe used the NRAO AIPS package for the data reduction. \nWe applied standard fringe-fitting, amplitude and phase (self-) calibration \ntechniques and produced hybrid maps of each quasar. \nThe astrometric analysis was done using two different mapping methods: \na ``standard'' phase-referencing approach, transferring phase solutions\nfrom one quasar to the other\n(see e.g. Alef \\cite{alef88}; Beasley \\& Conway \\cite{beasley95}) and a \nnovel mapping method for astrometry of close pairs\nof sources, hybrid double mapping (HDM) (Porcas \\& Rioja \\cite{porcas96}). \nBoth routes preserve the signature of the relative separation of the source \npair present in the calibrated phases. These analysis paths are described \nin Sects. 3.1 to 3.3 below. \n\n\\subsection{Hybrid mapping in AIPS} \n\nWe applied standard VLBI hybrid mapping\ntechniques in AIPS for the analysis of the observations of both\nquasars A and B. We used the\ninformation on system temperature, gain curves and telescope gains measured at\nthe individual array elements, to calibrate the raw correlation\ncoefficients. \nWe used the AIPS task FRING to estimate residual antenna-based phases\nand phase derivatives (delay and rate) at intervals of a few minutes.\nIt is important to realise that FRING is a global self-calibration\nalgorithm, and performs an initial phase self-calibration also. We ran\nFRING on the A quasar data set, with a point-source input model.\n\nAnticipating our phase-referencing scheme (Sect. 3.2) we applied the antenna\nphase, delay and rate solutions from A to both the A and B data sets, and\naveraged them in time to 60 s, and over the total observed bandwidth of 32 MHz.\nAfter suitable editing of the data, we made hybrid maps of both quasars,\nusing a number of iterations of a cycle including the mapping task MX and\nfurther phase self-calibration with CALIB.\n\nFig.~\\ref{fig1}a and b show the hybrid maps for both sources at 3.6~cm \nin 1995.9. \nThe maps are made using uniform weighting of the visibilities, a map\ncell size of 0.15 mas and a circular CLEAN restoring beam of 0.5 mas\n(these same mapping parameters are used throughout this work).\nThe ``dirty'' beam has a central peak of 0.57 x 0.47 mas in PA -29\\degr\n(PA = position angle, defined starting at North, increasing through East).\nThe root-mean-square (rms) levels in the A and B maps, in regions away \nfrom the source structures (estimated using AIPS task IMSTAT) are 1.0 and \n0.12 mJy/beam respectively, an indication that dynamic range considerations \ndominate over thermal noise in determining the map noise levels. \n\n%%% FIGURE 1\n\n\\begin{figure*}\n\\centerline{\n{\\psfig{figure=fig1a.ps,width=6.cm}}\n\\put (-150,150) {\\bf {a)}}\n{\\psfig{figure=fig1b.ps,width=6.cm}}\n\\put (-150,150) {\\bf {b)}}\n}\n\\caption{VLBI hybrid maps of 1038+528 at 3.6~cm. Uniform weighting, \nCLEAN beam 0.5 x 0.5 mas, pixel size 0.15 mas, tick interval 1 mas.\n{\\bf a} Quasar A. Contours at 3,6,12,24... mJy/beam.\n{\\bf b} Quasar B. Contours at 1.5,3,6,12... mJy/beam.\n\\label{fig1}} \n\\end{figure*}\n\n\\subsection{Phase referencing in AIPS}\n\nIn order to make an astrometric estimate of the separation between\nquasars A and B at this 4th epoch, we first used a \"conventional\" \nphase-reference\ntechnique to make maps of the quasars which preserve the relative phase\ninformation.\nIn practice this consists of using the antenna-based residual terms \nderived from the analysis of the data of one ``reference'' source (A), \nto calibrate the data from simultaneous observations of the other \"target\" \nsource (B).\nThe reference quasar source structure must first \nbe estimated from a hybrid map, and then fed back into\nthe phase self-calibration process to produce estimates of the antenna-based \nresiduals, free from contamination by source structure. \n\nPhase referencing techniques work under the assumption that the\nangular separation between the reference and target sources is smaller\nthan the isoplanatic patch size (i.e. the effects of unmodelled perturbations,\nintroduced by the propagation medium,\non the observed phases of both sources are not very different) and that \nany instrumental terms are common. Geometric errors in the correlator model\nmust also be negligible.\n\nAssuming that the antenna residuals have been ``cleanly'' estimated using the\nreference source data, the calibrated phases of the target \nsource should be free from the errors mentioned above, but still retain the\ndesired signature of the source structure and relative position\ncontributions. The Fourier Transformation of the calibrated visibility\nfunction of the target source produces a ``phase referenced'' map. The\noffset of the brightness distribution from the centre of this map reflects\nany error in the assumed relative separation in the correlator model.\nIf the reference source has a true ``point'' structure and is at the\ncentre of its hybrid map, this offset will be equal to the error;\nmore generally, one should also measure the offset of a\nreference point in the reference source map, and estimate the\nerror in the source separation used in the correlator model from the difference\nbetween the target and reference source offsets.\n\nIn general, the success of the phase-referencing technique is critically\ndependent on the angular separation of the target and reference sources.\nSimultaneous observation of the sources, as was possible here, significantly \nsimplifies the procedure, eliminates the need for temporal interpolation,\nand reduces the propagation of errors introduced in the\nanalysis. While random errors increase the noise level in the phase\nreferenced map, systematic errors may bias the estimated angular\nseparation.\n\nFor our implementation of phase-referencing using AIPS, we chose\nto re-FRING the (calibrated) A data set, using our hybrid map of quasar \nA as an input model, and applied the adjustments to the antenna phase, \ndelay and rate solutions to both the A and B data sets before re-averaging. \nWe then made maps of both A and B using MX, performing no further phase \nself-calibration. These are our ``phase-reference astrometry'' (PRA) \nmaps (shown in Fig.~\\ref{fig2}a and b) on which we performed\nastrometric measurements (see Sect. 4.2). Although the rms noise levels \nin the PRA maps are slightly higher than in the corresponding hybrid maps \n(2.0~mJy~beam$^{-1}$ for A and 0.24~mJy~beam$^{-1}$ for B),\nour procedure ensures that the A and B\nvisibility functions from which they are derived have been calibrated \nidentically. \n\n%%% FIGURE 2\n\n\\begin{figure*}\n\\centerline{\n{\\psfig{figure=fig2a.ps,width=6.cm}}\n\\put (-150,150) {\\bf {a)}}\n\\put (-84.5,88.5) {\\bf {+}}\n{\\psfig{figure=fig2b.ps,width=6.cm}}\n\\put (-150,150) {\\bf {b)}}\n\\put (-85,88) {\\bf {+}}\n}\n\\caption{VLBI phase-reference astrometry maps. Map parameters as in Fig. 1.\nAstrometry reference points are indicated with a cross.\n{\\bf a} Quasar A. Contours at 3.5,7,14,28... mJy~beam$^{-1}$.\n{\\bf b} Quasar B. Contours at 1.5,3,6,12... mJy~beam$^{-1}$.\n\\label{fig2}} \n\\end{figure*}\n\n\n\\subsection{New mapping method for astrometry of close source pairs} \n\nWhile the conventional phase-referencing approach worked well for our\nNovember 1995 observations of 1038+52A and B, the method relies on\nmaking a good estimate of the antenna residuals from just one of the \nsources - the reference. We have devised an alternative method which\nextends the standard VLBI self-calibration procedure to work on both\nsources together, for cases where they have been observed simultaneously,\nand when either could be used as the reference (see Appendix A).\n\nThe basis of the new method is to recognise that, since the visibility \nfunctions for both sources are corrupted by the same (antenna-based) \nphase and phase derivative errors, the sum of the two visibilities also \nsuffers the same errors. We form the point-by-point sum of the two data \nsets, creating a new one which represents the visibility function of a \n``compound source'' consisting of a superposition of the two structures, \ncorrupted by the common antenna phase errors.\nIf the source separation is close enough, the (summed) data as\na function of the (averaged) uv-coordinates can be\nFourier Transformed to form a map of the\ncompound source structure, and (iterative) self-calibration in FRING or CALIB\nyields the antenna-based residuals. The advantage of this approach is that\nthe antenna-based residuals are determined using both source structures\nsimultaneously, and may thus reduce the chance that reference source structural\nphase terms contaminate the residuals. We term this process ``Hybrid Double\nMapping'' (HDM); a detailed description is given in Porcas \\& Rioja \n(\\cite{porcas96}).\n\nIt is convenient to shift the source position in one of the data\nsets (by introducing artificial phase corrections)\nprior to the combination into a compound-source data set, to avoid \nsuperposition of the images in the map. The phase self-calibration \nsteps which are then applied to the combined data set are \nidentical to the case of a single source. In HDM the information\non the angular separation between the sources is preserved in the \nprocess of self-calibration of the combined visibilities, and can be measured\ndirectly from the compound-image map;\nthe relative positions between the individual source images in the \ncompound map, taken together with any artificial position shift introduced,\ngive the error in the assumed angular separation in the correlator model. \nIn this approach one must be careful to use the same number of visibility\nmeasurements in each time interval from the two data sets, in order to avoid\nthe predominance of data from a particular source. \n\nFig.~\\ref{fig3} shows the HDM map of quasars A and B in 1995.9 at \n$\\lambda$ 3.6~cm; \nthe B source is artificially offset by -4 mas in declination.\nThe rms noise in the map is 0.82~mJy~beam$^{-1}$ - higher than that in \nthe hybrid map of B but lower than in that of A.\n\n\n%%%FIGURE 3\n\n\\begin{figure}[h]\n\\centerline{\n{\\psfig{figure=fig3.ps,width=6.cm}}\n}\n\\caption{HDM map of 1038+52 (A+B). Map parameters as in Fig. 1. \nQuasar B has been offset by -4.0 mas in\ndeclination. Contours at 3,6,12,24... mJy~beam$^{-1}$. \n\\label{fig3}} \n\\end{figure}\n\n\n\n\\section{Analysis of the maps} \n\n\\subsection{Source structures} \n\nThe 1995.9 hybrid maps of quasars A and B at $\\lambda$ 3.6~cm \n(Fig.~\\ref{fig1}) show the core-jet structures typical of quasars at \nmas scales. They may be compared with maps from previous epochs given \nin Rioja et al. (\\cite{rioja97}). \nThe structure of A in the new map shows no major changes with respect \nto previous epochs. There is a prominent peak at the SW end of the\nstructure (the ``core'') and a jet extending in PA 15--25\\degr\n~containing at least two ``knot'' components (k1 and k2).\n\nThe new map of B at 3.6~cm is qualitatively similar to\nthose from previous epochs. It shows 2 point-like components separated\nby just under 2 mas in PA 127\\degr.\nSpectral arguments support the identification of\nthe NW component as a ``core'' (Marcaide \\& Shapiro \\cite{marca84}); \nthe SE component, corresponding to a knot in the jet, has been used as \na reference component in previous astrometric studies.\nThe separation between these 2 components in 1995.9 has increased, \ncontinuing the expansion along the axis of the source, as discovered \nfrom previous epochs of observations at this wavelength (Rioja et al. \n\\cite{rioja97}).\nThere is no trace of the third, extreme SE component, seen in maps\nof this source at 13~cm. This feature is evidently of lower surface\nbrightness at 3.6~cm and is resolved out at the resolution of these \nobservations.\n\nWe used AIPS task IMSTAT to estimate total flux densities for quasars A and\nB (within windows surrounding the sources in the hybrid maps). The values \nare given in Table~\\ref{tab1}.\nTable~\\ref{tab1} also lists the fluxes and relative positions of the \nmost prominent features in the maps of A and B, obtained using task JMFIT to\nfind parameters of elliptical Gaussian functions which best\nfit the various source sub-components. The formal errors from the fits,\nhowever, do not give realisitic values for the parameter uncertainties.\nThe distribution of flux between the core and k1 in quasar A, and their\nrelative separation, are quite uncertain, for example. \n\n%%%TABLE 1\n\\begin{table*}\n\\caption {Parameters derived from the Hybrid Maps of 1038+528 A and B.} \n\n\\vspace*{0.25cm}\n\n\\begin{center}\n\\begin{tabular} {|c|c|c|c|c|c|c|c|c|c|} \\hline\n & S-tot & & S-pk & S-int & maj.& min. & PA & sep. & PA \\\\\n & (mJy) & &(mJy/b) & (mJy) & (mas) & (mas) & (deg) & (mas) & (deg) \\\\\n\\hline\n1038+528 A & 603.0 & core & 301.6 & 355.3 & 0.28 & 0.12 & 3 & - & - \\\\\n & & k1 & 171.8 & 235.5 & 0.42 & 0.16 & 13 & 0.639 & 15.1 \\\\\n & & k2 & 9.3 & 14.0 & - & - & - & 1.796 & 24.8 \\\\\n&&&&&&&&& \\\\\n1038+528 B & 86.5 & core & 33.5 & 40.9 & 0.32 & 0.11 & 132 & - & - \\\\\n & & ref & 24.6 & 34.4 & 0.39 & 0.24 & 123 & 1.869 & 127.1 \\\\ \n\\hline \\hline\n\\end{tabular}\n\\end {center}\n\\label{tab1}\n\\end{table*}\n\n\n\\subsection{Estimating positions of reference features} \n\nThe astrometric measurement of a separation between two non-point sources\nmust always refer to the measured positions of reference points within \nmaps (or other representations) of the source structures. \nThe selection of suitable reference points is crucial in monitoring\nprograms, where the results from the analysis of a multi-epoch \nseries of observations are compared. \nIdeally, a reference point should correspond to the peak of\na strong, unresolved component, which is well separated from\nother radio emission within the source structure.\n\nFor the 1995.9 epoch observations of 1038+528 A,B we selected the same \nreference features as those used for the analyses of previous observing \nepochs. These are the ''core'' component for quasar A, and the prominent \nSE component for quasar B.\nThese features are labelled with a cross in Fig.~\\ref{fig2}a and b.\nThe core of A is indeed strong and compact, but has the disadvantage\nthat it merges with knot k1.\nAlthough the SE component of B is no longer the strongest feature at 3.6~cm,\nit has always been strong at both 3.6 and 13~cm wavelengths,\nis reasonably compact and is easily distinguishable\nin maps made at longer wavelengths, thus facilitating spectral studies.\nOur astrometric analysis refers to the measured positions of the peaks\nof these components in A and B. We used the AIPS task MAXFIT to measure \nthe position of these peaks in the PRA and HDM maps.\nMAXFIT defines the location of a peak in a given map region by fitting \na quadratic function to the peak pixel value and those of the adjacent pixels.\nA comparison of this method of defining the peak position with that used\nfor earlier epochs is described in the next section. \n\n\\subsection{Position error analysis} \n\nAn analysis of errors presented in Rioja et al. (\\cite{rioja97}) shows \nthat the dominant uncertainty in the astrometric measurements of the \nseparation between this close pair of quasars comes from the limited \nreproducibility of the reference point positions in the VLBI maps, \nfrom epoch to epoch. The magnitude of this effect\nis hard to quantify, however, since it depends on the nature of the\nsource brightness distribution surrounding the reference point, and\nthe method used to define the position of the peak, in addition\nto the resolution of the array and the signal-to-noise\nratio of the peak in the map.\n\nA rough estimate of the error due solely to finite signal-to-noise in\nthe maps is given by dividing the beam size by the ratio of the\ncomponent peak to the rms noise level in the maps (see e.g. \nThompson et al. \\cite{thompson86}). \nThis yields values of 3.3, 3.5 and 1.4~$\\mu$as for the A and B PRA \nmaps and the HDM map. These may be taken to represent lower limits to \nthe reference point position errors; realistic errors will be larger,\nand will depend on the nature of the reference features \nand the manner in which the position is estimated.\n\nIt is important to choose a definition of the reference point position \nsuch that it can be reproduced reliably from epoch to epoch, and is as \nindependent as possible from the parameters used in making the map \n(e.g. cell size and beam width).\nThe AIPS task JMFIT can be used to fit an elliptical Gaussian to a component\nin a CLEAN map, for example. However, the position of the peak of the \nGaussian depends on how asymmetric the component brightness distribution \nis, and the area of the map to which the fit is restricted. MAXFIT fits \njust to the local maximum around the peak map value, and is thus less \nsensitive to the rest of the distribution.\n\nWe have attempted to quantify some limits to reproducibility arising from \nthe use of MAXFIT for defining the peak position in CLEAN maps.\nWe investigated the effect of changing the true position of a point-like\nsource with respect to the pixel sampling (here 3.3 pixels per beam) \nby offsetting the source position in 10 increments of 1/10 of a pixel \nin the visibility domain, mapping and CLEANing the new data sets, and \nestimating the new positions in the CLEAN maps using MAXFIT. The\nmaximum discrepancy found between the values of the artificial offset\nand the shift derived by MAXFIT was 1/20 of a pixel.\nThis corresponds to 8~$\\mu$as in our 3.6~cm maps.\n\nFor the analysis of previous observing epochs, the reference points\nwere defined to be the centroid of the most prominent delta functions \nfrom which the CLEAN source map was derived (Rioja et al. \\cite{rioja97}).\nWe examined possible systematic differences resulting from these\ndifferent definitions of reference points.\nOne might expect the largest discrepancies to arise when the underlying\nsource structure near the reference point is asymmetric, as in quasar A.\nWe investigated such differences by determining ``centroid'' positions for\nboth A and B reference components, using various criteria for excluding\nclean components from the calculation; this included the ``25 percent\nof the value at the peak'' threshold used for earlier epochs.\nFor A the difference between this centroid position and the MAXFIT\nvalue was 0.12 pixel (18~$\\mu$as). For B the difference was less\nthan 0.1 pixel.\nThese are probably the largest potential sources of error arising from using\ndifferent methodologies at different epochs.\n\nOur use of two different mapping procedures - phase-reference mapping\nand HDM - also gives some insight into the size of position errors resulting\nfrom standard CLEAN + phase self-cal mapping algorithms.\nThe differences between the separation estimates from the PRA maps and the\nHDM map are 27 and 28~$\\mu$as in RA and Dec respectively.\nThis would suggest that differences in the positions of peaks in \nmaps reconstructed in different ways may vary at the 14~$\\mu$as level.\n\nAfter considering the various possible effects which can limit the\naccuracy of postion estimates, we adopt a ``conservative'' value for \nthe error in estimating the peak position in our $\\lambda$ 3.6~cm maps,\nembracing all the effects detailed above, of $18~\\mu$as\n(this corresponds to a thirtieth of the CLEAN beam).\nThe associated estimated error for a separation measurement between\nthe two sources is $25~\\mu$as.\n\n\n\\subsection{Astrometry results} \n\nTable~\\ref{tab2} lists the results of our astrometric measurements of \nreference point positions in the maps.\nThey are presented as changes in measured separation between the \nreference points in A and B in 1995.9, with respect to their separation \nin 1981.3. \nThe values given from the phase-reference technique correspond to the \ndifference between the A and B reference feature position offsets in \ntheir respective PRA map. The values derived from HDM have been corrected \nfor the artificial offset introduced before adding the A and B source \nvisibilities.\n\n%%%TABLE 2\n\n\\begin{table}\n\\caption{Change in the separation between quasars A and B in 1995.9\nwith respect to 1981.2, estimated using standard phase referencing \n(PRA) and hybrid double mapping (HDM) techniques.}\n\\begin{center}\n\n\\vspace*{0.25cm}\n\n\\begin{tabular} {|c| c| c|} \\hline \n$\\Delta(\\Delta \\alpha)$ $\\cos \\delta_A$ & $\\Delta(\\Delta \\delta)$ & Method \\\\ \n$[\\mu$as$]$ & $[\\mu$as$]$ & \\\\ \\hline \\hline\n% (%) = Without Correlator position offset: RA -159muas; DEC 74 muas\n% 11 & 175 & Phase Referencing \\\\\n -148 & 249 & PRA \\\\\n% -16 & 203 & HDM$^1$ \\\\\n% -175 & 277 & HDM$^1$ \\\\ \\hline \\hline\n -175 & 277 & HDM \\\\ \\hline \\hline\n% -7.5 & 204 & HDM$^2$ \\\\\n% -167 & 278 & HDM$^2$ \\\\\n% -9 & 180 & HDM$^3$ \\\\ \\hline\n% -168 & 254 & HDM$^3$ \\\\ \\hline\n\\end{tabular}\n\\end{center}\n\\label{tab2}\n\\end{table}\n\n\nAll these values have been corrected for a small error in the AIPS calculation\nof the u,v coordinates in the frequency-averaged data set.\n(Distances measured within the maps must be adjusted\nby a small correction factor of\n$1 - \\Delta \\nu \\ast (2~\\nu)^{-1} = 0.998$.) \n \\\\\n\nTable~\\ref{tab3} lists the coordinates of the reference source (A) adopted in\nthe analysis and the measured coordinate separation between quasars A\nand B in 1995.9.\n\n%%%TABLE 3\n\n\\begin{table*}\n\\caption{{\\it Fixed} source coordinates used for quasar A\nin the astrometric analysis (these coordinates correspond to GSFC global\nsolution GLB831 (Chopo Ma, priv. comm.)), and\nseparation between quasars A and B measured in 1995.9.}\n\n\\begin{center}\n\n\\vspace*{0.25cm}\n\n\\begin{tabular} { |l| r| r|} \\hline\n{\\bf Coordinates} & {\\bf RA} (J2000) \\hspace*{0.5cm} & {\\bf DEC} (J2000) \\hspace*{0.5cm}\n \\\\ \\hline \\hline\n{\\it Reference Source {\\bf (A)}} & 10$^h$ 41$^m$ 46\\fs781613 \n\\hspace*{0.05cm} & 52$^0$ 33\\arcmin 28\\farcs23373 \\hspace*{0.05cm} \\\\ \\hline \n{\\it Relative Sep. {\\bf (B-A)}} & $2\\fs1160588 $ \n& $27\\farcs376325$ \\\\\n{\\it Estimated error {\\bf (B-A)}} & $\\pm 0\\fs0000027$ & $ \\pm 0\\farcs000025$ \\\\ \\hline\n\\end{tabular}\n\\end{center}\n\\label{tab3}\n\\end{table*}\n\n\n\\section{Comparison of astrometry at all 4 epochs} \n\nIn this section we make a comparison of the astrometric\nmeasurements from the series of 4 epochs of observations.\nAny increase of the temporal baseline in the program of monitoring the \nseparation between A and B should result in a more precise \nidentification of any systematic trends,\nwith an improved elimination of random contributions.\nIn Sect. 5.1 we justify comparing\nthe astrometric values measured at the various epochs, even\nthough non-identical observing, post-processing and analysis\nprocedures were involved.\nIn Sect. 5.2 we present the astrometric results from the 4 epochs.\nIn Sects. 5.3, 5.4, 5.5 and 5.6 we present various analyses of these\nresults, and attempt to quantify, or put upper-limits to,\nproper motions within and between the A and B quasars.\n\n\n\\subsection{Comparison between the techniques used at different epochs}\n\nBefore attempting a comparison of the astrometric results from \nthe 4 observing epochs, we need to\nshow that any bias in the astrometric estimates introduced by the\nuse of different procedures is small compared with other errors in\nthe measurements for the individual epochs.\nThe consistency between the results from previous epochs of observations \nhas been exhaustively tested (Marcaide et al. \\cite{marca94}; \nRioja et al. \\cite{rioja97}).\nWe outline here the largest changes involved in the fourth epoch, 1995.9,\nwith respect to previous ones:\n\n\\begin{enumerate}\n\n\\item The observing array and frequency set-up used in the fourth epoch\nwas different from previous epochs of observations \n(frequency range 8404.5 to 8436.5 MHz instead of 8402.99 to 8430.99 MHz\nat first 3 epochs). This results in a different coverage of the {\\it UV} \nplane, leading to changes in the reconstruction of the source images. \nInvestigations of such effects by Marcaide et al. (\\cite{marca94}) show that\nthe effect on the astrometric anaylsis is only a few $\\mu$as. \nIt is important to note that the observations at all 4 epochs have\ncomparable resolutions and sample the same range of structural scales\nin the sources.\n\n\\item The processing of the fourth epoch was done using the VLBA correlator,\nwhich uses a theoretical model derived from CALC 8.2; we used AIPS to\nanalyse the data with visibility phases residual to that model.\nFor previous epochs the correlation was done at the MPIfR (Bonn) MK3\ncorrelator, and an analysis of the data using total phases was made\nwith VLBI3 (Robertson \\cite{robertson75}).\nThe differences between CALC 8.2 and the one implemented in VLBI3 \npropagate into changes of only 1-2~$\\mu$as in the astrometric analysis\nof the 1038+528 A-B separation (Rioja \\cite{rioja93}, Rioja et al. \n\\cite{rioja97}). \nThis is because any such differences are ``diluted'' by the source \nseparation expressed in radians - \n$10^{-4}$ in the case of this very close source pair.\n\n\\item The values used in the analysis of previous epochs for\nEarth Orientation Parameters (EOP), stations and reference source coordinates\nwere consistently derived from a single global solution provided by Goddard \nSpace Flight Center (GSFC). \nFor the correlation of the fourth epoch, the values used for \nEOP were derived from IERS solutions, and the station coordinates from \nUSNO catalogs.\nWe have made a comparison of the values derived for all the parameters at\nthe 4 epochs from a single global solution from IERS (namely IERS eopc04),\nwith the actual values\nused in the individual epoch analysis. The difference between the corresponding\nEOP values is always less than 4 mas. Such discrepancies propagate into \nerrors in the relative position estimates at each epoch of only a few \n$\\mu$as.\n\n\\item Our astrometric analysis in AIPS using a phase-referencing approach and\nHDM differs from the phase difference method used in VLBI3 analysis.\nComparisons show that these procedures are equivalent \n(Porcas \\& Rioja \\cite{porcas96}; Thompson et al. \\cite{thompson86}).\nBoth involve the definition of reference points in source maps;\nuncertainties in the reference point positions \n(as described in Sect. 4.3) arise in the same way.\n\n\\item Finally, a minor VLBA correlator error (Romney priv. comm.) caused\nincorrect time labels to be attached to the visibility records, resulting in\nincorrect ({\\it u,v}) values. \nThe effect on the relative visibility phases for our source pair is small\n($\\sim 0.004$\\degr) and can be neglected.\n\n\\end{enumerate}\n\n The magnitudes of all of the effects reported in this section are\nmuch smaller than our estimate in Sect. 4.3 of the uncertainity in reproducing\nthe reference point in the source, from epoch to epoch, and we are thus\njustified in comparing the astrometric results from all 4 epochs.\n\n\n\\subsection{Astrometric separations at the 4 epochs} \n\nThe astrometric measurements of the separations between the reference \npoints in A and B at $\\lambda$ 3.6~cm from 4 epochs are presented in \nFig.~\\ref{fig4}.\nIt includes our new 1995.9 measurement and those from three earlier epochs, \nin 1981.3, 1983.4 and 1990.5, reported in Marcaide \\& Shapiro \n(\\cite{marca84}), Marcaide et al. (1994) and Rioja et al. (\\cite{rioja97}), \nrespectively. The origin of the plot represents the separation at epoch 1.\n\n%%% FIGURE 4\n\n\\begin{figure}[h]\n\\centerline{\n{\\psfig{figure=fig4.ps,width=6.cm}}\n}\n\\caption{Measured separations between the A and B reference points at epochs\n2 (1983.4), 3 (1990.5) and 4 (1995.9), with respect to epoch 1 (1981.2).\nPlotted error bars correspond to $25~\\mu$as.\n\\label{fig4}} \n\\end{figure}\n\n\nChanges with time in Fig.~\\ref{fig4} represent the vector difference between\nany motions of the reference points in quasars A and B.\nThe near-orthogonal nature of the source axes in 1038+52 A,B (along\nwhich one might expect any motion to occur) simplifies the\ninterpretation of any trends seen. The new 1995.9 value follows the\nsame steady trend towards the NW shown by the three previous epochs.\nRioja et al. (\\cite{rioja97}) interpreted this as an outward expansion of the\nreference component in quasar B at a rate of $18~\\pm~5~\\mu$as~yr$^{-1}$, \nand quoted an upper bound on any proper motion of quasar A of \n$10~\\mu$as~yr$^{-1}$.\n\n\\subsection{Vector decomposition} \n\nIn this section we attempt to separate the individual contributions from \nthe 2 quasars in the astrometric separation measurements presented in \nFig.~\\ref{fig4}. We make no assumption about the stability of either \ncomponent, but\nassume that any displacements of the A or B reference points from their \npositions at epoch 1 are along the corresponding source axis directions.\nThis is a plausible assumption if the reference point coincides \nwith a non-stationary component moving along a ballistic trajectory, \nor with the location of the peak of brightness within an active core \nor near the base of jet, where changes during episodes of activity are \nlikely to occur along the jet direction.\nThis approach is closely related to that used previously \nby Rioja et al. (\\cite{rioja97}). For fixed assumed source axes for A and B,\nit results in a unique decomposition of the changes in the A-B separation\ninto separate A and B displacements, from 1981 to 1995.\n\nIt is clear that the dominant contribution to the separation changes\nseen in Fig.~\\ref{fig4} comes from quasar B, \nin which the source axis is well defined by the 127\\degr PA of\nthe separation between core and reference components.\nFor quasar A the source axis bends, from the inner ``core'' region \n(PA = 15\\degr) to the outer jet components, and it is not so clear which \ndirection should be chosen.\n\nIn our analysis we tried a range of values for fixing the A source axis \n(0 to 45\\degr ~in steps of 5\\degr).\nFor each, we calculated A and B reference-point displacements at epochs 2, \n3 and 4 with respect to epoch 1.\nThen we performed a least-squares fit to the B displacements with time to\nestimate a linear expansion rate for the B reference feature along \nPA 127\\degr. In Fig.~\\ref{fig5} we plot the deconvolved B reference point \ndisplacements from the analysis with the A source axis fixed at \nPA 25\\degr (the value adopted by Rioja et al. \\cite{rioja97}).\nThe fitted expansion rate is $16.9~\\pm~0.6~\\mu$as~yr$^{-1}$;\nthe error and associated rms values take account of the small number \nof points and 2 degrees of freedom. This rate agrees well with the value\nof $18~\\pm~5~\\mu$as~yr$^{-1}$ deduced by Rioja et al. (\\cite{rioja97}).\nThe rms residual from the fit (7~$\\mu$as) is low, and vindicates\nour use of measurements derived from differing techniques for\ninvestigating the relative proper motion between A and B. \n\n%%% FIGURE 5\n\n\\begin{figure}[h]\n\\centerline{\n{\\psfig{figure=fig5.ps,width=6.cm}}\n}\n\\caption{Changes in position of reference component in B along PA 127\\degr,\ndeduced from deconvolution of the A-B separation measurements. Assumed source\naxis for A is 25\\degr.\nPlotted error bars correspond to $25~\\mu$as.\n\\label{fig5}} \n\\end{figure}\n\n\n\\subsection{Structural evolution within 1038+528 B} \n\nOur deconvolution analysis of the changes in separation measured between \nall 4 epochs supports the finding, previously proposed, that the B reference\ncomponent moves along the source axis, away from the B core.\nIn this section we make an independent determination of the separation \nrate between the core and reference component in B from measurements \nwithin the maps at the 4 epochs.\n\nFig.~\\ref{fig6} shows the separation between the core and reference \ncomponent in B at the four epochs plotted against time. For epochs 1--3 \nwe used the values given in Rioja et al. (\\cite{rioja97}). For 1995.9 we \nused AIPS task UVFIT to estimate a separation from the B visibility data \ndirectly, in order to follow the methodology used for the other epochs as \nclosely as possible; the value obtained was 1.895 mas.\nThe slope from a least-squares fit corresponds to an expansion rate \nof $13.0~\\pm~0.7~\\mu$as~yr$^{-1}$.\nIn the standard picture of extragalactic radio sources, the ``core'' is\nstationary, so this corresponds to an outward expansion of the\nreference component along PA 127\\degr.\n\n%%% FIGURE 6\n\n\\begin{figure}[h]\n\\centerline{\n{\\psfig{figure=fig6.ps,width=6.cm}}\n}\n\\caption{Changes in the position of the reference component in B \nalong PA 127\\degr, from measurements of its separation from the core\nin hybrid maps of B.\nPlotted error bars correspond to $25~\\mu$as.\n\\label{fig6}} \n\\end{figure}\n\n\nThe rms of the fit (8~$\\mu$as) is again surprisingly low, implying\ntypical errors in the separation measurements at each epoch \n(both within the B structure and between the reference points)\nof only about 10--12$~\\mu$as along the direction of the B source axis.\nThis is considerably less than the estimate of position separation \nerrors given in Sect. 4.3. \n\n\\subsection{Relative proper motion }\n\nThe analysis presented in the previous sections demonstrate\nclearly that the chosen reference component within quasar B is\nunsuitable for use as a marker for tracing any relative proper motion\nbetween quasars A and B. The value of its expansion velocity derived \nin Sect. 5.4 appears to differ significantly from that deduced by \nvector-decomposition in Sect. 5.3. Although the difference between \nthese estimates, if real, could be interpreted as motion of the core of B \nat a rate of $\\sim 4~\\mu$as~yr$^{-1}$, this is not a conclusive result\nsince differences of this order arise from choosing different values of \nPA for the motion in A in the vector decomposition method.\n\nA more suitable tracer of relative proper motion between the quasars is \nthe variation of the separation between the cores of A and B.\nWe have used the separations between the core and reference component\nmeasured in the B map at each epoch, and the astrometric\nseparations between A and B, to calculate the separations between the\nA and B cores at each epoch; these are plotted in Fig.~\\ref{fig7}.\nThe area occupied by the points defines an upper limit of \n$\\sim 10~\\mu$as~yr$^{-1}$ for any relative proper motion between \nthe A and B cores, and hence between the quasars themselves, during\nthe period of nearly 15 years for which the separation has been\nmonitored with VLBI.\nThe limit seems to be set by the relatively large deviation of the\n1995.9 epoch point in the direction of the A source axis, presumably\narising from the difficulty in defining the reference point at the\nA ``core'' from epoch to epoch. \n\n%%% FIGURE 7\n\n\\begin{figure}[h]\n\\centerline{\n{\\psfig{figure=fig7.ps,width=6.cm}}\n}\n\\caption{Separation between the cores of A and B (with respect to epoch 1),\nderived by correcting the A-B reference point separation measurements with the\ncore-reference separations measured in the B hybrid maps.\nPlotted error bars correspond to $25~\\mu$as.\n\\label{fig7}} \n\\end{figure}\n\n\n\\subsection{Possible ``core'' motions ? } \n\nFinally, we investigate any possible residual motions of the ``cores'' \nin A and B. The most likely causes of any such apparent motions are \nchanges in the relative brightness or positions of features in the \nsource structures at a resolution below that of the maps.\nOne might expect that these, too, would produce effects predominantly\nalong the source axis directions.\nWe therefore used the vector deconvolution method on the plot of\ncore-core separation with time to study displacements of the cores\nalong their source axis directions.\nFig.~\\ref{fig8}a and b show plots of the separated contributions from \nB and A, for an assumed A source axis PA 25\\degr.\nThe displacements for the B core seem to increase systematically.\nThe fitted rate is $3.8~\\pm~0.3~\\mu$as~yr$^{-1}$, indicating a possible \nslow outward motion. The displacements for the A core do not seem to \nvary systematically - the fitted slope is $5.5~\\pm~3.6~\\mu$as~yr$^{-1}$.\nHere the scatter is considerably larger, reflecting both the difficulties of\ndefining the reference point along the A core-jet axis, and\nalso, perhaps, real ``jitter'' of the position of the peak due to variations \nin the ``core'' substructure. These plots indicate the level of stability \nof the individual core positions; the fits represent realistic upper limits \nto any possible systematic core motion in the A and B quasars along their \nsource axis directions.\n\n%%% FIGURE 8\n\n\\begin{figure*}\n\\centerline{\n{\\psfig{figure=fig8a.ps,width=6.cm}}\n\\put (-140,140) {\\bf {a)}}\n{\\psfig{figure=fig8b.ps,width=6.cm}}\n\\put (-130,140) {\\bf {b)}}\n}\n\\caption{Residual motions of the cores using the deconvolution approach.\n {\\bf a} Displacements of B core along PA 127\\degr; \n{\\bf b} Displacements of A core along PA 25\\degr. \nPlotted error bars correspond to $25~\\mu$as.\n\\label{fig8}} \n\\end{figure*}\n\n\n\\section{Conclusions} \n\nThe series of astrometric VLBI measurements of the separation between \nthe quasar pair 1038+528 A and B, spanning\nnearly 15 years, provides excellent material for investigating \nthe relative proper motion of two extragalactic radio sources and\nthe positional stability of their cores.\nThe changes measured in the separations between quasars A and B \nat 3.6~cm are dominated by the motion of the reference feature in quasar B. \nThese astrometric results, and measurements in the hybrid maps of B are\ncompatible with an expansion rate for the B reference component of \n13--17$~\\mu$as~yr$^{-1}$.\nAt a redshift of 2.296 this translates to an apparent\ntransverse velocity of 0.55--0.70~c~h$^{-1}$.\nWe note that this is an order of magnitude smaller than the more\ntypical superluminal velocities seen in many quasars; it is a \nrare example of a subluminal velocity measured for a knot in a quasar jet.\n\nAfter correcting for the motion of the reference component in B,\nwe can put a conservative upper bound to any relative proper\nmotion between the quasars of $10~\\mu$as~yr$^{-1}$.\nDespite the increase in temporal baseline, this upper bound is no\nbetter than that given by Rioja et al. (\\cite{rioja97}).\nIts value is related to the difficulty in reproducing a stable reference\nposition along the A source axis near its ``core''.\n\nTheories in which the redshifts of quasars do not indicate cosmological\ndistances, and in which quasars are ``local'' and have high Doppler\nredshifts (e.g. Narlikar \\& Subramanian \\cite{narlikar83}) are incompatible \nwith our measured upper-limit to relative proper motion. Quasars at \n100 Mpc distance moving at relativistic speeds would have proper motions \nof the order of $600~\\mu$as~yr$^{-1}$, nearly 2 orders of magnitude \ngreater than our limit. Assuming cosmological distances,\nour limit corresponds to apparent transverse velocities of \n0.43~c~h$^{-1}$ and 0.22~c~h$^{-1}$ at the redshifts of the B and A\nquasars, respectively.\n\nWe have investigated the way in which the definition of \nreference points in a map may be only loosely ``fixed'' to the radio\nsource structure, especially when the latter is strongly asymmetric.\nWe have also developed an alternative analysis route - Hybrid Double\nMapping - for imaging both sources of a close pair simultaneously, and\nat the same time preserving their relative astrometric information\nin a single map.\n\nThe surprisingly low rms from the fits of linear expansion in quasar B,\nand the discrepancy between the two estimates \n($16.9~\\pm~0.6~\\mu$as~yr$^{-1}$ from the astrometric measurements and\n $ 13.0~\\pm~0.7~\\mu$as~yr$^{-1}$ from the hybrid maps)\nare suggestive of (but do not prove) a residual motion of the core \nin quasar B; our decomposition along the source axis direction gives a fit\nof $3.8~\\pm~0.3~\\mu$as~yr$^{-1}$, corresponding to an apparent transverse \nvelocity of 0.17~c~h$^{-1}$. If real, this might indicate a steady change \nin physical conditions at the base of the jet, or perhaps the emergence \nof a new knot component moving outwards with a velocity similar to the \nreference component, but as yet unresolved by our 0.5 mas beam.\nIn this regard, it is interesting to note the slight extension of\nthe core of quasar B in PA 132\\degr given by the Gaussian model fit.\n\nThe low rms derived from fits to the expansion of the B reference component \nindicate that we have been overly conservative in our estimate of \n$18~\\mu$as for the error in reference point positions. Errors at least \n2 times smaller are implied, corresponding to a sixtieth of the beamwidth. \nIt is interesting to note that such small errors are also implied in the \nwork of Owsianik \\& Conway (\\cite{owsianik98}), where the low scatter in \nthe plot of expansion of the CSO source \\object{0710+439} allows an \nexpansion rate of $14.1~\\pm~1.6~\\mu$as~yr$^{-1}$ to be determined.\n\nThere are no obvious systematic motions within quasar A, but the ``noise'' \nin the estimates of position along its axis are much larger.\nThis noise, along with any associated underlying changes in source\nsubstructure, provides a fundamental limit to estimates of\nany systematic core motion in A. Improvements on the estimates of (or upper\nbounds to) the relative motion between the quasars, or of the\nindividual motion of the A core, will require a considerable\nincrease in the temporal baseline of VLBI monitoring.\n\n\\newpage\n\n\\appendix \n\n\\section {Hybrid Double Mappping (HDM)}\n\n\n{\\bf A.1 Principle of Hybrid Double Mapping} \\\\\n\n\\noindent\nThe visibility function, $V$, measured at time $t$, on a baseline between\nantennas $i$ and $j$, is represented by a complex function with amplitude $A$, \nphase $P$:\n\n\\[ V(i,j) = A * e^{i[\\phi]}(t) \\]\n\n\\noindent\nFor this analysis it is convenient to indentify 3 contributions to\nthe visibility phase:\n\n\\[ \\phi(i,j) = \\phi_{s}(u,v) + \\phi_{p}(u,v) + \\phi_{m}(t) \\]\n\n\\noindent\nwhere \n\n\\begin{description} \n\\item [$\\phi_s$] is due to source structure, evaluated w.r.t. a reference\nposition for the source. \\\\\n\n \\item [$\\phi_p$] is due to any offset of the \ntrue source position from the reference position. \\\\\n\nBoth $\\phi_s$ and \n$\\phi_p$ are functions of the resolution coordinates, $u$ and $v$, at time \n$t$. \\\\\n\n\\item [$\\phi_m$] is due to inaccuracies in the correlator model calculation of\n the interferometer geometry and the signal propagation delays\n in the ionosphere, troposphere and receiving system; it is an \n unknown function of time. \\\\\n This term can be represented by the difference of two\n ''antenna-based'' phases, $\\theta_i$ and $\\theta_j$, since it can \n be related to the \n difference in signal arrival times at the two sites.\n (This analysis is a simplification which ignores possible\n ''non-closing'' instrumental baseline phase terms arising from\n e.g. un-matched bandpasses and polarisation impurities.) \n\\end{description}\n\n\\[ \\phi(i,j) = \\phi_s(u,v) + \\phi_p(u,v) + \\theta_i(t) - \\theta_j(t) \\]\n\n\\noindent\nIn conventional hybrid mapping, an iterative procedure is used\nto separate out the antenna-based phase terms from the ''source'' terms;\nthe latter must produce a consistent and physically plausible source\nstructure after Fourier transformation of the corrected visibility:\n\n\\[ \\underbrace {A * e^{i[\\phi_s+\\phi_p]}(u,v)}_{corrected \\: visibility} = \nV(i,j) * \\underbrace {e^{-i[\\theta_i(t)-\\theta_j(t)]}}_{antenna \\: phase \\: terms} \\] \n\n\\noindent\nHowever, the position offset term, $\\phi_p$, can also be expressed as a difference \nin wavefront arrival times at the 2 antennas and so it is also\n''absorbed'' in antenna phase terms $\\theta_i'$, $\\theta_j'$; \nthe ''absolute'' position information is lost:\n\n\\[ \\underbrace {A * e^{i[\\phi_s]}(u,v)}_{corrected \\: visibility} = \nV(i,j) * \\underbrace {e^{-i[\\theta_i'(t)-\\theta_j'(t)]}}_{antenna \\: phase\n\\: terms} \\]\n\n\\noindent\nIn Hybrid Double Mapping (HDM), the visibility functions of two \nsources observed simultaneously are added. For a close source pair, we \nmake the same assumption as for conventional phase-referencing - that the \nmodel error phase terms are essentially the same for both sources. We make \na further assumption that the $u,v$ coordinates are also essentially the same\nfor both sources, for each baseline and time. The visibility sum, $V^1 + V^2$,\ncan then be re-written: \\\\\n\n\n\\[ \\underbrace {(A^1 * e^{i[\\phi^1_{s}]} + A^2 * e^{i[\\phi^2_{s}+(\\phi^2_{p}\n-\\phi^1_{p})]})(u,v)}_{corrected \\: visibility \\: sum} = \\]\n\\[ \\;\\;\\; \\vspace*{2cm} = V^{sum}(i,j) * \\underbrace {e^{-i[\\theta_i'(t)-\\theta_j'(t)]}}_{antenna \\:\n phase \\: terms} \\] \n\n\n%\\begin{eqnarray*}\n%\\lefteqn{ \\[ \\underbrace {(A_1e^{i[\\phi_{1s}]}+A_2e^{i[\\phi_{2s}+(\\phi_{2p}-\\phi_{1p})]})(u,v)}_{corrected \\: visibility \\: sum} = } \\\\\n%& & V^{sum}(i,j) * \\underbrace {e^{-i[\\theta_i'(t)-\\theta_j'(t)]}}_{antenna \\:\n%phase \\: terms} \\] \n%\\end{eqnarray*}\n\n\\noindent\nThis may be recognised as the visibility function of a ''composite''\nsource consisting of the sum of the brightness distributions of sources\n1 and 2, with antenna-based phase error terms $\\theta_i'$, $\\theta_j'$, \nas before.\nThe HDM method consists of performing the normal hybrid mapping\nprocedure with the visibility sum, resulting in the separation of the\nantenna-based errors, and a physically plausible map of the sum of\nthe two source brightness distrubutions. An important point is that,\nwhereas the {\\it origin} of the map of the composite source is arbitrary (as\nit depends on the position of the starting model), the {\\it separation} of\nthe two source brightness distributions within the composite map\n(determined by $\\phi^2_{p}-\\phi^1_{p}$) is fixed during the phase \nseparation procedure,\nand is equal to the {\\it difference} of the errors in the two source\npositions used for correlation. We call this the ''residual separation''. \\\\\n\n\\noindent\n{\\bf A.2 Practical aspects} \\\\\n\n\\noindent\nThere are some practical aspects to be considered. If the source\ncoordinates used in the correlator model are very precise, then the\nresidual separation may be less than the interferometer beamwidth, and\nthe two source distributions will lie on top of each other. \nIn this case it is desireable to\nintroduce an artificial position offset into one of the\nsource visibility functions before forming the visibility sum, to\nensure that the two source reference features are well separated in the\nHDM map. One should also arrange that the peak of one source\ndoes not lie on the sidelobe response of the other in the \"dirty\" map,\nas this may degrade the CLEAN deconvolution process in the mapping step.\\\\\n\n\\noindent\n Another important consideration is that the time-averaged samples\nof the summed visibility function contain equal contributions from both\nsource visibility functions. When both sources are observed\nsimultaneously this will normally be the case, except when different\namounts of data are lost in the two separate correlator passes needed\nfor the two source positions. It is important to edit the data sets\ncarefully to fulfil this condition. \\\\\n\n\\noindent\n The range of validity of the assumption that the $(u,v)$\ncoordinates for the two sources are the same depends on the ''dilution\nfactor'', i.e. the reciprocal of the source separation, measured in\nradians. The $(u,v)$ value assigned to the summed visibility will be\nincorrect for either source by roughly 1 part in the dilution factor\n(roughly 1 in 6000 for 1038+528A,B). \nThis is equivalent to having source visibility phase errors of this\norder, and thus limits the size of an HDM map to be less than the\nbeamwidth times the dilution factor; the residual separation should be\nmuch smaller than this value.\\\\\n\n\\noindent\nIn the actual analysis used in this work, we first made a rough \ncorrection to the phase of the summed visibility of 1038+528 A + B, using\nthe antenna phase and phase derivative errors from fringe-fitting\n1038+528A using a point source model. However, there is no reason why\none should not fringe-fit the summed visibility function directly. \\\\\n\n\\noindent\n{\\bf A.3 Applications} \\\\\n\n\\noindent\nThe HDM method can in principle be applied\nwhenever two (or more !) radio sources are observed simultaneously,\nbut are correlated at separate field centres; however, \nthey must be close enough so that the conditions of same $(u,v)$\ncoverage and same correlator model errors apply.\nThe method uses the structures of BOTH sources simultaneously to\nseparate out the antenna phase errors, as opposed to a single source in \nsimple hybrid mapping.\nIf both sources are strong (as with 1038+528 A and B),\nconstraining the (single) antenna phase solutions with two structures\nshould lead to a more rigorous and robust separation between the\nsource and antenna phase terms.\nOne field of application is in high resolution VLBI imaging of\ngravitational lens systems with wide image separations (e.g. \nimages A and B of QSO 0957+561 with 6.1 arcsec separation)\nwhere preserving the necessary wide field-of-view from a single \ncorrelation may result in inconveniently large data sets.\nWhen one source is very weak, however,\nthere is probably little to be gained over normal hybrid mapping. \\\\\n\n\\noindent\nFor relative astrometry studies (as described in this paper),\nthe HDM method has some advantages over conventional phase-reference \nmapping and explicit phase-differencing methods.\nIn phase-differencing astrometry, separate hybrid maps must be made of\nboth sources to correct for source structural phase terms and \nthe antenna phase errors are NOT constrained to be the same. Imperfect \nseparation between source and antenna phase terms can increase the noise \non the differenced phase, as well as lead to possible systematic errors.\nIn phase-reference astrometry, only one of the sources is used to solve\nfor the antenna phase terms; imperfect separation can lead to extra\nphase noise in the phase-referenced visibility of the ''target'' source.\nIn HDM we use both source\nstructures simultaneously to separate the (common) antenna error\nphases from that of a single \"structure\" in which the \nreference points of the two sources are spaced by the residual separation.\\\\\n\n\\noindent\nWhen the separation between the two sources of a pair exceeds\nthe telescope primary beamwidths, astrometric and phase-reference \nobservations \nmust involve switching between the sources, and the visibility phase of at \nleast one of the sources must normally be interpolated in the observing gap. \nThe condition that must be fulfilled for HDM to work in\nthis case is that an equal number of observations of both sources must\nbe added to form an average visibility function for the length of the\n''solution interval'' in the phase self-calibration step of HDM.\nThis length is generally limited by the coherence time of the\natmosphere, and would imply a very fast switching cycle in most cases.\nAnother application for HDM could be in the the analysis of\n''cluster-cluster'' VLBI (see e.g. Rioja et al. \\cite{rioja97b}), \nin which two or more sources are observed simultaneously on VLBI baselines \nby using more than one telescope at each site.\n\n\n\\begin{acknowledgements}\n\nWe thank Dave Graham for help with the observations in Effelsberg,\nTony Beasley for asistance at the VLBA, and Mark Reid for useful comments\non the text. M.J.R. wishes to acknowledge support for this research by the\nEuropean Union under contract CHGECT920011.\nThe National Radio Astronomy Observatory is a facility\nof the National Science Foundation operated under cooperative\nagreement by Associated Universities, Inc.\n\n\\end{acknowledgements}\n\n\\begin{thebibliography}{}\n\n\\bibitem[1988]{alef88} Alef W.A., 1988, in Proc. IAU Symp. 129, \ned. Reid M., Moran J., Kluwer, p. \\ 523 \n\n\\bibitem[1995]{beasley95} Beasley A.J., Conway J.E., 1995, \nVery Long Baseline Interferometry and the VLBA, eds. Zensus J.A., \nDiamond P.J., Napier P.J., ASP Conference Series, Vol. 82, p. \\ 327.\n\n\\bibitem[1986]{blandford86} Blandford R.D., K\\\"onigl A., 1986, \nApJ 308, 83\n\n\\bibitem[1983]{marca83} Marcaide J.M., Shapiro I.I., 1983, AJ 88, 1133 \n\\bibitem[1984]{marca84} Marcaide J.M., Shapiro I.I., 1984, ApJ 276, 56\n\\bibitem[1994]{marca94} Marcaide J.M., El\\'{o}segui P., Shapiro I.I., 1994, \n AJ 108, 368 \n\\bibitem[1983]{narlikar83} Narlikar J.V., Subramanian K., 1983, \nApJ 273, 44\n\\bibitem[1978]{owen78} Owen F.N., Porcas R.W., Neff S.G., 1978, \nAJ 83, 1009\n\\bibitem[1980]{owen80} Owen F.N., Wills B.J., Wills D., 1980, ApJ 235, L57\n\\bibitem[1998]{owsianik98} Owsianik I., Conway J.E., 1998, A\\&A 337, 69\n\\bibitem[1986]{porcas87} Porcas R.W., 1987, Superluminal Radio Sources, ed.\n Zensus A., Pearson A., Cambridge University Press, p. \\ 12\n\\bibitem[1996]{porcas96} Porcas R.W., Rioja M.J., 1996, Proc. of the 11th \nWorking Meeting on European VLBI for Geodesy and Astrometry, Ed. Elgered\nG., p. \\ 209\n\\bibitem[1993]{rioja93} Rioja M.J., 1993, PhD. Thesis, Universidad de Granada\n\\bibitem[1997]{rioja97} Rioja M.J., Marcaide J.M., El\\'osegui P., \nShapiro I.I., 1997, A\\&A 325, 383 \n\\bibitem[1997]{rioja97b} Rioja M.J., Stevens E.,\nGurvits L., et al., 1997, {\\it Vistas in Astronomy} 41 (2), 213 \n%\\bibitem[2000]{rioja00} Rioja, M.J., Porcas, R.W., 2000, {\\it in preparation}\n\\bibitem[1975]{robertson75} Robertson D.S., 1975, PhD Thesis, MIT\n%\\bibitem[1996]{romney96} Romney, J.D., 1996, (VLBA email memorandum \n%of 14 March) \n\\bibitem[1986]{thompson86} Thompson A.R., Moran J.M., Swenson G.W., 1986, \nInterferometry and Synthesis in Radio Astronomy. Wiley-Interscience, \nNew York, p. 400\n\n\\end{thebibliography}{}\n\n\n\n\n\\end{document}\n\n"}],"string":"[\n {\n \"name\": \"rioja_17jan2000.tex\",\n \"string\": \"% aa.dem\\n% AA vers. 4.01, LaTeX class for Astronomy & Astrophysics\\n% demonstration file\\n% (c) Springer-Verlag HD\\n%-----------------------------------------------------------------------\\n%\\n%\\\\documentclass[referee]{aa} % for a referee version\\n%\\n\\\\documentclass{aa}\\n%\\n\\\\usepackage{psfig}\\n\\n\\\\begin{document}\\n\\n \\\\thesaurus{03 % A&A Section 3: Extragalactic astronomy\\n (03.09.2; % Instrumentation: interferometers,\\n 03.20.2; % Techniques: interferometric, \\n 05.01.1; % Astrometry,\\n 13.18.2)} % Radio continuum: general.\\n%\\n \\\\title{A phase-reference study of the quasar pair 1038+528A,B }\\n% \\\\title{A phase-reference study of the}\\n% \\\\subtitle{quasar pair 1038+528A,B }\\n\\n% \\\\subtitle{I. Overviewing the $\\\\kappa$-mechanism}\\n\\n \\\\author{Mar\\\\'{\\\\i}a J. Rioja \\n \\\\inst{1}\\n \\\\inst{2}\\n \\\\and\\n Richard W. Porcas\\\\inst{3}\\n% \\\\fnmsep\\\\thanks{Just to show the usage\\n% of the elements in the author field}\\n }\\n\\n \\\\offprints{Mar\\\\'{\\\\i}a J. Rioja}\\n\\n \\\\institute{Observatorio Astron\\\\'omico Nacional (OAN), Apdo. 1143, \\n E-28800 Alcal\\\\'a de Henares, Spain \\\\\\\\\\n email: rioja@oan.es\\n \\\\and\\n Joint Institute for VLBI in Europe (JIVE), \\n NL-7990 AA Dwingeloo, The Netherlands \\\\\\\\\\n \\\\and\\n Max-Planck Institut f\\\\\\\"ur Radioastronomie, Auf dem H\\\\\\\"ugel 69,\\n D-53121 Bonn, Germany \\\\\\\\\\n email: porcas@mpifr-bonn.mpg.de \\n% \\\\thanks{The university of heaven temporarily does not\\n% accept e-mails}\\n }\\n\\n \\\\date{Received 5 October, 1999; accepted XX }\\n\\n \\\\titlerunning{Relative Astrometry of 1038+528AB}\\n \\\\authorrunning{Rioja \\\\& Porcas}\\n\\n \\\\maketitle\\n \\n \\\\begin{abstract}\\n\\nWe present results from $\\\\lambda$ 3.6~cm observations of the quasar pair \\n\\\\object{1038+528} A and B, made in 1995 using the VLBA together with the \\nEffelsberg 100m telescope. We describe the use of a phase-referencing \\ntechnique to measure the astrometric separation between the quasars.\\nWe also introduce a new data analysis method - \\\"hybrid double mapping\\\" - \\nwhich preserves the relative astrometric information in a single VLBI \\nhybrid map for close source pairs. We combine our measurements with those \\nfrom three previous epochs, the earliest in 1981. \\nOur new observations confirm the evolution within the structure of quasar B, \\npreviously proposed to explain the measured change in the relative separation \\nof the pair. Our upper bound for any systematic proper motion between the \\nmass centres of quasars A and B is 10~$\\\\mu$as~yr$^{-1}$. This is set by the \\nlimited precision in defining the reference points in the quasars at \\ndifferent epochs and by possible instabilities of the source \\\"core\\\" locations.\\nA separate analysis enables us to put more stringent upper limits to any \\ncore motions along the two source axes.\\n\\n \\\\keywords{Instrumentation: interferometers --\\n Techniques: interferometric --\\n Astrometry --\\n Radio continuum: general\\n }\\n \\\\end{abstract}\\n\\n%\\n%________________________________________________________________\\n\\n\\\\section{Introduction}\\n\\nThe quasar pair 1038+528~A,B (Owen et al. \\\\cite{owen78}) \\nconsists of two\\nflat-spectrum radio sources, with redshifts 0.678 and 2.296 (Owen et\\nal. \\\\cite{owen80}), separated on the sky by only 33\\\\arcsec. \\nThis system provides a unique opportunity to carry out high precision, relative\\nastrometric studies using the full\\nprecision of VLBI relative phase measurements, \\nsince most sources of phase errors are common for the 2 sources\\n(Marcaide \\\\& Shapiro \\\\cite{marca83}).\\n\\n VLBI studies of the mas-scale structure of flat-spectrum quasars\\nshow that they typically have ``core-jet'' morphologies, consisting of a highly\\ncompact feature (the ``core'') located at the base of an extended linear feature \\nor line of lower brightness components (the ``jet'').\\nBoth 1038+528 A and B exhibit such structures.\\nIn standard models of extragalactic radio sources, these radio-emitting \\nfeatures\\narise from a collimated beam of plasma which is ejected with a highly \\nrelativistic bulk velocity from a region close to a central massive object \\nsuch as a black hole (see eg. Blandford \\\\& K\\\\\\\"onigl \\\\cite{blandford86}).\\nWhilst jet features may correspond to shocks in the moving plasma, and \\ncan give rise to the observed ``superluminal'' component motions in some \\nsources (Porcas \\\\cite{porcas87}),\\nthe ``core'' emission is thought to arise from a more-or-less permanent location close to\\nthe origin of the beam, where the ambient conditions correspond to a transition\\nfrom optically thick to optically thin emission at the observed frequency.\\nAlthough the ``core'' position may thus be frequency-dependent, for a fixed\\nobserving frequency\\nthe core should provide a stable marker, anchored to the central mass of\\nthe quasar, whose location can be used to define a precise position for\\nthe object as a whole.\\nAlthough short time-scale variations in physical conditions may cause\\nsmall changes in the ``core'' location, over long time-scales it may be\\nused to track any systematic proper motion of the quasar.\\n\\nThe results from a near decade-long VLBI monitoring program on 1038+52A,B at\\n$\\\\lambda$ 3.6 and 13~cm (from 1981.2 to 1990.5) \\nare reported by Rioja et al. (\\\\cite{rioja97}), whose main conclusions \\ncan be summarized as follows:\\n\\n\\\\begin{enumerate}\\n\\n\\\\item There is no evidence of any relative proper motion between the \\n quasars A and B. The uncertainties in the astrometric parameters \\n result in an upper bound to any systematic relative \\n motion between the cores of 10~$\\\\mu$as~yr$^{-1}$, consistent\\n with zero.\\n\\n\\\\item A compact feature within the jet of quasar B, chosen as the \\n reference point for the structure, expands away from the core at \\n a steady, slow rate of $\\\\sim~18~\\\\pm~5~\\\\mu$as~yr$^{-1}$, corresponding \\n to v=$(0.8~\\\\pm~0.2)~h^{-1}$~c for a Hubble constant,\\n H$_0$ = 100~h~km~s$^{-1}$~Mpc$^{-1}$; q$_0=0.5$. These values are used \\n here throughout.\\n\\n\\\\item The accuracy of the relative separation measurement is limited by \\n noise and source structure, with estimated precisions of about \\n $50~\\\\mu$as at $\\\\lambda$ 3.6~cm at any epoch.\\n\\n\\\\item Confirmation of the consistently large offset (about 0.7 mas) between\\n the positions of the peak of brightness (``core'') at $\\\\lambda$ 3.6 \\n and 13~cm in quasar A.\\n\\n\\\\end{enumerate}\\n\\nNew VLBI observations of this pair were made in November 1995 (1995.9) \\nat $\\\\lambda$ 2, 3.6 and 13~cm. In this paper we report on results from \\nour analysis of the 3.6~cm observations and investigate the temporal \\nevolution of the source structures and relative separation from all \\nfour epochs spanning $\\\\sim 15$ years. \\nInvestigations of frequency-dependent source structure have also been made \\nfrom a comparison of the astrometric measurements\\nof the separations between A and B at all 3 wavelengths observed in 1995;\\nthese will be presented elsewhere (Rioja \\\\& Porcas in preparation).\\n\\nOur new observations are described in Sect. 2. In Sect. 3 we describe\\nthe data reduction and mapping techniques used, and in Sect. 4 an analysis\\nof the measurements in the maps.\\nIn Sect. 5 we compare the astrometric results from these observations\\nwith those from previous epochs and analyse the changes in \\nseparation. Conclusions are presented in Sect. 6.\\n\\n%__________________________________________________________________\\n\\n\\\\section{Observations}\\n\\nThe pair of radio sources 1038+528 A and B was observed with the\\nNRAO Very Long Baseline Array (VLBA) on November 10, 1995,\\nfor a total of 13 hours, alternating every 13 minutes between\\nobservations in dual 3.6/13~cm mode and observations at 2~cm. The\\n100m telescope at Effelsberg was also included in the array for the\\n3.6/13~cm scans. The primary beamwidths of all the antennas were\\nsufficiently large that both sources could be observed simultaneously\\nat all wavelengths. Each 10 minute observation of 1038+52A,B was\\npreceded by a 3 minute observation of the compact calibration source\\n\\\\object{0917+624}, to monitor the behaviour of the array.\\n\\nAll stations used VLBA terminals to record an aggregate \\nof 64 MHz bandwidth for each scan, using 1-bit sampling, subdivided into\\n8 channels (mode 128-8-1). For the dual 3.6/13~cm scans, four 8-MHz channels\\nwere recorded for each band (2254.5--2286.5 MHz; 8404.5--8436.5 MHz), \\nusing \\nRHC polarisation. At 2~cm, eight 8-MHz channels (15\\\\,331.5--15\\\\,395.5 MHz)\\nwere recorded in LHC polarisation.\\n\\nThe correlation was made at the VLBA correlator in Socorro (New Mexico).\\nAs for previous epochs, two separate ``passes'' were needed, using different \\nfield centres for the two sources, to recover data\\nfor both the A and B quasars from the single observation. \\nOutput data sets were generated for the two sources, consisting of the\\nvisibility functions averaged to 2 s, with samples every 1 MHz in frequency\\nacross the bands. \\n\\n\\\\section{Data reduction} \\n\\nWe used the NRAO AIPS package for the data reduction. \\nWe applied standard fringe-fitting, amplitude and phase (self-) calibration \\ntechniques and produced hybrid maps of each quasar. \\nThe astrometric analysis was done using two different mapping methods: \\na ``standard'' phase-referencing approach, transferring phase solutions\\nfrom one quasar to the other\\n(see e.g. Alef \\\\cite{alef88}; Beasley \\\\& Conway \\\\cite{beasley95}) and a \\nnovel mapping method for astrometry of close pairs\\nof sources, hybrid double mapping (HDM) (Porcas \\\\& Rioja \\\\cite{porcas96}). \\nBoth routes preserve the signature of the relative separation of the source \\npair present in the calibrated phases. These analysis paths are described \\nin Sects. 3.1 to 3.3 below. \\n\\n\\\\subsection{Hybrid mapping in AIPS} \\n\\nWe applied standard VLBI hybrid mapping\\ntechniques in AIPS for the analysis of the observations of both\\nquasars A and B. We used the\\ninformation on system temperature, gain curves and telescope gains measured at\\nthe individual array elements, to calibrate the raw correlation\\ncoefficients. \\nWe used the AIPS task FRING to estimate residual antenna-based phases\\nand phase derivatives (delay and rate) at intervals of a few minutes.\\nIt is important to realise that FRING is a global self-calibration\\nalgorithm, and performs an initial phase self-calibration also. We ran\\nFRING on the A quasar data set, with a point-source input model.\\n\\nAnticipating our phase-referencing scheme (Sect. 3.2) we applied the antenna\\nphase, delay and rate solutions from A to both the A and B data sets, and\\naveraged them in time to 60 s, and over the total observed bandwidth of 32 MHz.\\nAfter suitable editing of the data, we made hybrid maps of both quasars,\\nusing a number of iterations of a cycle including the mapping task MX and\\nfurther phase self-calibration with CALIB.\\n\\nFig.~\\\\ref{fig1}a and b show the hybrid maps for both sources at 3.6~cm \\nin 1995.9. \\nThe maps are made using uniform weighting of the visibilities, a map\\ncell size of 0.15 mas and a circular CLEAN restoring beam of 0.5 mas\\n(these same mapping parameters are used throughout this work).\\nThe ``dirty'' beam has a central peak of 0.57 x 0.47 mas in PA -29\\\\degr\\n(PA = position angle, defined starting at North, increasing through East).\\nThe root-mean-square (rms) levels in the A and B maps, in regions away \\nfrom the source structures (estimated using AIPS task IMSTAT) are 1.0 and \\n0.12 mJy/beam respectively, an indication that dynamic range considerations \\ndominate over thermal noise in determining the map noise levels. \\n\\n%%% FIGURE 1\\n\\n\\\\begin{figure*}\\n\\\\centerline{\\n{\\\\psfig{figure=fig1a.ps,width=6.cm}}\\n\\\\put (-150,150) {\\\\bf {a)}}\\n{\\\\psfig{figure=fig1b.ps,width=6.cm}}\\n\\\\put (-150,150) {\\\\bf {b)}}\\n}\\n\\\\caption{VLBI hybrid maps of 1038+528 at 3.6~cm. Uniform weighting, \\nCLEAN beam 0.5 x 0.5 mas, pixel size 0.15 mas, tick interval 1 mas.\\n{\\\\bf a} Quasar A. Contours at 3,6,12,24... mJy/beam.\\n{\\\\bf b} Quasar B. Contours at 1.5,3,6,12... mJy/beam.\\n\\\\label{fig1}} \\n\\\\end{figure*}\\n\\n\\\\subsection{Phase referencing in AIPS}\\n\\nIn order to make an astrometric estimate of the separation between\\nquasars A and B at this 4th epoch, we first used a \\\"conventional\\\" \\nphase-reference\\ntechnique to make maps of the quasars which preserve the relative phase\\ninformation.\\nIn practice this consists of using the antenna-based residual terms \\nderived from the analysis of the data of one ``reference'' source (A), \\nto calibrate the data from simultaneous observations of the other \\\"target\\\" \\nsource (B).\\nThe reference quasar source structure must first \\nbe estimated from a hybrid map, and then fed back into\\nthe phase self-calibration process to produce estimates of the antenna-based \\nresiduals, free from contamination by source structure. \\n\\nPhase referencing techniques work under the assumption that the\\nangular separation between the reference and target sources is smaller\\nthan the isoplanatic patch size (i.e. the effects of unmodelled perturbations,\\nintroduced by the propagation medium,\\non the observed phases of both sources are not very different) and that \\nany instrumental terms are common. Geometric errors in the correlator model\\nmust also be negligible.\\n\\nAssuming that the antenna residuals have been ``cleanly'' estimated using the\\nreference source data, the calibrated phases of the target \\nsource should be free from the errors mentioned above, but still retain the\\ndesired signature of the source structure and relative position\\ncontributions. The Fourier Transformation of the calibrated visibility\\nfunction of the target source produces a ``phase referenced'' map. The\\noffset of the brightness distribution from the centre of this map reflects\\nany error in the assumed relative separation in the correlator model.\\nIf the reference source has a true ``point'' structure and is at the\\ncentre of its hybrid map, this offset will be equal to the error;\\nmore generally, one should also measure the offset of a\\nreference point in the reference source map, and estimate the\\nerror in the source separation used in the correlator model from the difference\\nbetween the target and reference source offsets.\\n\\nIn general, the success of the phase-referencing technique is critically\\ndependent on the angular separation of the target and reference sources.\\nSimultaneous observation of the sources, as was possible here, significantly \\nsimplifies the procedure, eliminates the need for temporal interpolation,\\nand reduces the propagation of errors introduced in the\\nanalysis. While random errors increase the noise level in the phase\\nreferenced map, systematic errors may bias the estimated angular\\nseparation.\\n\\nFor our implementation of phase-referencing using AIPS, we chose\\nto re-FRING the (calibrated) A data set, using our hybrid map of quasar \\nA as an input model, and applied the adjustments to the antenna phase, \\ndelay and rate solutions to both the A and B data sets before re-averaging. \\nWe then made maps of both A and B using MX, performing no further phase \\nself-calibration. These are our ``phase-reference astrometry'' (PRA) \\nmaps (shown in Fig.~\\\\ref{fig2}a and b) on which we performed\\nastrometric measurements (see Sect. 4.2). Although the rms noise levels \\nin the PRA maps are slightly higher than in the corresponding hybrid maps \\n(2.0~mJy~beam$^{-1}$ for A and 0.24~mJy~beam$^{-1}$ for B),\\nour procedure ensures that the A and B\\nvisibility functions from which they are derived have been calibrated \\nidentically. \\n\\n%%% FIGURE 2\\n\\n\\\\begin{figure*}\\n\\\\centerline{\\n{\\\\psfig{figure=fig2a.ps,width=6.cm}}\\n\\\\put (-150,150) {\\\\bf {a)}}\\n\\\\put (-84.5,88.5) {\\\\bf {+}}\\n{\\\\psfig{figure=fig2b.ps,width=6.cm}}\\n\\\\put (-150,150) {\\\\bf {b)}}\\n\\\\put (-85,88) {\\\\bf {+}}\\n}\\n\\\\caption{VLBI phase-reference astrometry maps. Map parameters as in Fig. 1.\\nAstrometry reference points are indicated with a cross.\\n{\\\\bf a} Quasar A. Contours at 3.5,7,14,28... mJy~beam$^{-1}$.\\n{\\\\bf b} Quasar B. Contours at 1.5,3,6,12... mJy~beam$^{-1}$.\\n\\\\label{fig2}} \\n\\\\end{figure*}\\n\\n\\n\\\\subsection{New mapping method for astrometry of close source pairs} \\n\\nWhile the conventional phase-referencing approach worked well for our\\nNovember 1995 observations of 1038+52A and B, the method relies on\\nmaking a good estimate of the antenna residuals from just one of the \\nsources - the reference. We have devised an alternative method which\\nextends the standard VLBI self-calibration procedure to work on both\\nsources together, for cases where they have been observed simultaneously,\\nand when either could be used as the reference (see Appendix A).\\n\\nThe basis of the new method is to recognise that, since the visibility \\nfunctions for both sources are corrupted by the same (antenna-based) \\nphase and phase derivative errors, the sum of the two visibilities also \\nsuffers the same errors. We form the point-by-point sum of the two data \\nsets, creating a new one which represents the visibility function of a \\n``compound source'' consisting of a superposition of the two structures, \\ncorrupted by the common antenna phase errors.\\nIf the source separation is close enough, the (summed) data as\\na function of the (averaged) uv-coordinates can be\\nFourier Transformed to form a map of the\\ncompound source structure, and (iterative) self-calibration in FRING or CALIB\\nyields the antenna-based residuals. The advantage of this approach is that\\nthe antenna-based residuals are determined using both source structures\\nsimultaneously, and may thus reduce the chance that reference source structural\\nphase terms contaminate the residuals. We term this process ``Hybrid Double\\nMapping'' (HDM); a detailed description is given in Porcas \\\\& Rioja \\n(\\\\cite{porcas96}).\\n\\nIt is convenient to shift the source position in one of the data\\nsets (by introducing artificial phase corrections)\\nprior to the combination into a compound-source data set, to avoid \\nsuperposition of the images in the map. The phase self-calibration \\nsteps which are then applied to the combined data set are \\nidentical to the case of a single source. In HDM the information\\non the angular separation between the sources is preserved in the \\nprocess of self-calibration of the combined visibilities, and can be measured\\ndirectly from the compound-image map;\\nthe relative positions between the individual source images in the \\ncompound map, taken together with any artificial position shift introduced,\\ngive the error in the assumed angular separation in the correlator model. \\nIn this approach one must be careful to use the same number of visibility\\nmeasurements in each time interval from the two data sets, in order to avoid\\nthe predominance of data from a particular source. \\n\\nFig.~\\\\ref{fig3} shows the HDM map of quasars A and B in 1995.9 at \\n$\\\\lambda$ 3.6~cm; \\nthe B source is artificially offset by -4 mas in declination.\\nThe rms noise in the map is 0.82~mJy~beam$^{-1}$ - higher than that in \\nthe hybrid map of B but lower than in that of A.\\n\\n\\n%%%FIGURE 3\\n\\n\\\\begin{figure}[h]\\n\\\\centerline{\\n{\\\\psfig{figure=fig3.ps,width=6.cm}}\\n}\\n\\\\caption{HDM map of 1038+52 (A+B). Map parameters as in Fig. 1. \\nQuasar B has been offset by -4.0 mas in\\ndeclination. Contours at 3,6,12,24... mJy~beam$^{-1}$. \\n\\\\label{fig3}} \\n\\\\end{figure}\\n\\n\\n\\n\\\\section{Analysis of the maps} \\n\\n\\\\subsection{Source structures} \\n\\nThe 1995.9 hybrid maps of quasars A and B at $\\\\lambda$ 3.6~cm \\n(Fig.~\\\\ref{fig1}) show the core-jet structures typical of quasars at \\nmas scales. They may be compared with maps from previous epochs given \\nin Rioja et al. (\\\\cite{rioja97}). \\nThe structure of A in the new map shows no major changes with respect \\nto previous epochs. There is a prominent peak at the SW end of the\\nstructure (the ``core'') and a jet extending in PA 15--25\\\\degr\\n~containing at least two ``knot'' components (k1 and k2).\\n\\nThe new map of B at 3.6~cm is qualitatively similar to\\nthose from previous epochs. It shows 2 point-like components separated\\nby just under 2 mas in PA 127\\\\degr.\\nSpectral arguments support the identification of\\nthe NW component as a ``core'' (Marcaide \\\\& Shapiro \\\\cite{marca84}); \\nthe SE component, corresponding to a knot in the jet, has been used as \\na reference component in previous astrometric studies.\\nThe separation between these 2 components in 1995.9 has increased, \\ncontinuing the expansion along the axis of the source, as discovered \\nfrom previous epochs of observations at this wavelength (Rioja et al. \\n\\\\cite{rioja97}).\\nThere is no trace of the third, extreme SE component, seen in maps\\nof this source at 13~cm. This feature is evidently of lower surface\\nbrightness at 3.6~cm and is resolved out at the resolution of these \\nobservations.\\n\\nWe used AIPS task IMSTAT to estimate total flux densities for quasars A and\\nB (within windows surrounding the sources in the hybrid maps). The values \\nare given in Table~\\\\ref{tab1}.\\nTable~\\\\ref{tab1} also lists the fluxes and relative positions of the \\nmost prominent features in the maps of A and B, obtained using task JMFIT to\\nfind parameters of elliptical Gaussian functions which best\\nfit the various source sub-components. The formal errors from the fits,\\nhowever, do not give realisitic values for the parameter uncertainties.\\nThe distribution of flux between the core and k1 in quasar A, and their\\nrelative separation, are quite uncertain, for example. \\n\\n%%%TABLE 1\\n\\\\begin{table*}\\n\\\\caption {Parameters derived from the Hybrid Maps of 1038+528 A and B.} \\n\\n\\\\vspace*{0.25cm}\\n\\n\\\\begin{center}\\n\\\\begin{tabular} {|c|c|c|c|c|c|c|c|c|c|} \\\\hline\\n & S-tot & & S-pk & S-int & maj.& min. & PA & sep. & PA \\\\\\\\\\n & (mJy) & &(mJy/b) & (mJy) & (mas) & (mas) & (deg) & (mas) & (deg) \\\\\\\\\\n\\\\hline\\n1038+528 A & 603.0 & core & 301.6 & 355.3 & 0.28 & 0.12 & 3 & - & - \\\\\\\\\\n & & k1 & 171.8 & 235.5 & 0.42 & 0.16 & 13 & 0.639 & 15.1 \\\\\\\\\\n & & k2 & 9.3 & 14.0 & - & - & - & 1.796 & 24.8 \\\\\\\\\\n&&&&&&&&& \\\\\\\\\\n1038+528 B & 86.5 & core & 33.5 & 40.9 & 0.32 & 0.11 & 132 & - & - \\\\\\\\\\n & & ref & 24.6 & 34.4 & 0.39 & 0.24 & 123 & 1.869 & 127.1 \\\\\\\\ \\n\\\\hline \\\\hline\\n\\\\end{tabular}\\n\\\\end {center}\\n\\\\label{tab1}\\n\\\\end{table*}\\n\\n\\n\\\\subsection{Estimating positions of reference features} \\n\\nThe astrometric measurement of a separation between two non-point sources\\nmust always refer to the measured positions of reference points within \\nmaps (or other representations) of the source structures. \\nThe selection of suitable reference points is crucial in monitoring\\nprograms, where the results from the analysis of a multi-epoch \\nseries of observations are compared. \\nIdeally, a reference point should correspond to the peak of\\na strong, unresolved component, which is well separated from\\nother radio emission within the source structure.\\n\\nFor the 1995.9 epoch observations of 1038+528 A,B we selected the same \\nreference features as those used for the analyses of previous observing \\nepochs. These are the ''core'' component for quasar A, and the prominent \\nSE component for quasar B.\\nThese features are labelled with a cross in Fig.~\\\\ref{fig2}a and b.\\nThe core of A is indeed strong and compact, but has the disadvantage\\nthat it merges with knot k1.\\nAlthough the SE component of B is no longer the strongest feature at 3.6~cm,\\nit has always been strong at both 3.6 and 13~cm wavelengths,\\nis reasonably compact and is easily distinguishable\\nin maps made at longer wavelengths, thus facilitating spectral studies.\\nOur astrometric analysis refers to the measured positions of the peaks\\nof these components in A and B. We used the AIPS task MAXFIT to measure \\nthe position of these peaks in the PRA and HDM maps.\\nMAXFIT defines the location of a peak in a given map region by fitting \\na quadratic function to the peak pixel value and those of the adjacent pixels.\\nA comparison of this method of defining the peak position with that used\\nfor earlier epochs is described in the next section. \\n\\n\\\\subsection{Position error analysis} \\n\\nAn analysis of errors presented in Rioja et al. (\\\\cite{rioja97}) shows \\nthat the dominant uncertainty in the astrometric measurements of the \\nseparation between this close pair of quasars comes from the limited \\nreproducibility of the reference point positions in the VLBI maps, \\nfrom epoch to epoch. The magnitude of this effect\\nis hard to quantify, however, since it depends on the nature of the\\nsource brightness distribution surrounding the reference point, and\\nthe method used to define the position of the peak, in addition\\nto the resolution of the array and the signal-to-noise\\nratio of the peak in the map.\\n\\nA rough estimate of the error due solely to finite signal-to-noise in\\nthe maps is given by dividing the beam size by the ratio of the\\ncomponent peak to the rms noise level in the maps (see e.g. \\nThompson et al. \\\\cite{thompson86}). \\nThis yields values of 3.3, 3.5 and 1.4~$\\\\mu$as for the A and B PRA \\nmaps and the HDM map. These may be taken to represent lower limits to \\nthe reference point position errors; realistic errors will be larger,\\nand will depend on the nature of the reference features \\nand the manner in which the position is estimated.\\n\\nIt is important to choose a definition of the reference point position \\nsuch that it can be reproduced reliably from epoch to epoch, and is as \\nindependent as possible from the parameters used in making the map \\n(e.g. cell size and beam width).\\nThe AIPS task JMFIT can be used to fit an elliptical Gaussian to a component\\nin a CLEAN map, for example. However, the position of the peak of the \\nGaussian depends on how asymmetric the component brightness distribution \\nis, and the area of the map to which the fit is restricted. MAXFIT fits \\njust to the local maximum around the peak map value, and is thus less \\nsensitive to the rest of the distribution.\\n\\nWe have attempted to quantify some limits to reproducibility arising from \\nthe use of MAXFIT for defining the peak position in CLEAN maps.\\nWe investigated the effect of changing the true position of a point-like\\nsource with respect to the pixel sampling (here 3.3 pixels per beam) \\nby offsetting the source position in 10 increments of 1/10 of a pixel \\nin the visibility domain, mapping and CLEANing the new data sets, and \\nestimating the new positions in the CLEAN maps using MAXFIT. The\\nmaximum discrepancy found between the values of the artificial offset\\nand the shift derived by MAXFIT was 1/20 of a pixel.\\nThis corresponds to 8~$\\\\mu$as in our 3.6~cm maps.\\n\\nFor the analysis of previous observing epochs, the reference points\\nwere defined to be the centroid of the most prominent delta functions \\nfrom which the CLEAN source map was derived (Rioja et al. \\\\cite{rioja97}).\\nWe examined possible systematic differences resulting from these\\ndifferent definitions of reference points.\\nOne might expect the largest discrepancies to arise when the underlying\\nsource structure near the reference point is asymmetric, as in quasar A.\\nWe investigated such differences by determining ``centroid'' positions for\\nboth A and B reference components, using various criteria for excluding\\nclean components from the calculation; this included the ``25 percent\\nof the value at the peak'' threshold used for earlier epochs.\\nFor A the difference between this centroid position and the MAXFIT\\nvalue was 0.12 pixel (18~$\\\\mu$as). For B the difference was less\\nthan 0.1 pixel.\\nThese are probably the largest potential sources of error arising from using\\ndifferent methodologies at different epochs.\\n\\nOur use of two different mapping procedures - phase-reference mapping\\nand HDM - also gives some insight into the size of position errors resulting\\nfrom standard CLEAN + phase self-cal mapping algorithms.\\nThe differences between the separation estimates from the PRA maps and the\\nHDM map are 27 and 28~$\\\\mu$as in RA and Dec respectively.\\nThis would suggest that differences in the positions of peaks in \\nmaps reconstructed in different ways may vary at the 14~$\\\\mu$as level.\\n\\nAfter considering the various possible effects which can limit the\\naccuracy of postion estimates, we adopt a ``conservative'' value for \\nthe error in estimating the peak position in our $\\\\lambda$ 3.6~cm maps,\\nembracing all the effects detailed above, of $18~\\\\mu$as\\n(this corresponds to a thirtieth of the CLEAN beam).\\nThe associated estimated error for a separation measurement between\\nthe two sources is $25~\\\\mu$as.\\n\\n\\n\\\\subsection{Astrometry results} \\n\\nTable~\\\\ref{tab2} lists the results of our astrometric measurements of \\nreference point positions in the maps.\\nThey are presented as changes in measured separation between the \\nreference points in A and B in 1995.9, with respect to their separation \\nin 1981.3. \\nThe values given from the phase-reference technique correspond to the \\ndifference between the A and B reference feature position offsets in \\ntheir respective PRA map. The values derived from HDM have been corrected \\nfor the artificial offset introduced before adding the A and B source \\nvisibilities.\\n\\n%%%TABLE 2\\n\\n\\\\begin{table}\\n\\\\caption{Change in the separation between quasars A and B in 1995.9\\nwith respect to 1981.2, estimated using standard phase referencing \\n(PRA) and hybrid double mapping (HDM) techniques.}\\n\\\\begin{center}\\n\\n\\\\vspace*{0.25cm}\\n\\n\\\\begin{tabular} {|c| c| c|} \\\\hline \\n$\\\\Delta(\\\\Delta \\\\alpha)$ $\\\\cos \\\\delta_A$ & $\\\\Delta(\\\\Delta \\\\delta)$ & Method \\\\\\\\ \\n$[\\\\mu$as$]$ & $[\\\\mu$as$]$ & \\\\\\\\ \\\\hline \\\\hline\\n% (%) = Without Correlator position offset: RA -159muas; DEC 74 muas\\n% 11 & 175 & Phase Referencing \\\\\\\\\\n -148 & 249 & PRA \\\\\\\\\\n% -16 & 203 & HDM$^1$ \\\\\\\\\\n% -175 & 277 & HDM$^1$ \\\\\\\\ \\\\hline \\\\hline\\n -175 & 277 & HDM \\\\\\\\ \\\\hline \\\\hline\\n% -7.5 & 204 & HDM$^2$ \\\\\\\\\\n% -167 & 278 & HDM$^2$ \\\\\\\\\\n% -9 & 180 & HDM$^3$ \\\\\\\\ \\\\hline\\n% -168 & 254 & HDM$^3$ \\\\\\\\ \\\\hline\\n\\\\end{tabular}\\n\\\\end{center}\\n\\\\label{tab2}\\n\\\\end{table}\\n\\n\\nAll these values have been corrected for a small error in the AIPS calculation\\nof the u,v coordinates in the frequency-averaged data set.\\n(Distances measured within the maps must be adjusted\\nby a small correction factor of\\n$1 - \\\\Delta \\\\nu \\\\ast (2~\\\\nu)^{-1} = 0.998$.) \\n \\\\\\\\\\n\\nTable~\\\\ref{tab3} lists the coordinates of the reference source (A) adopted in\\nthe analysis and the measured coordinate separation between quasars A\\nand B in 1995.9.\\n\\n%%%TABLE 3\\n\\n\\\\begin{table*}\\n\\\\caption{{\\\\it Fixed} source coordinates used for quasar A\\nin the astrometric analysis (these coordinates correspond to GSFC global\\nsolution GLB831 (Chopo Ma, priv. comm.)), and\\nseparation between quasars A and B measured in 1995.9.}\\n\\n\\\\begin{center}\\n\\n\\\\vspace*{0.25cm}\\n\\n\\\\begin{tabular} { |l| r| r|} \\\\hline\\n{\\\\bf Coordinates} & {\\\\bf RA} (J2000) \\\\hspace*{0.5cm} & {\\\\bf DEC} (J2000) \\\\hspace*{0.5cm}\\n \\\\\\\\ \\\\hline \\\\hline\\n{\\\\it Reference Source {\\\\bf (A)}} & 10$^h$ 41$^m$ 46\\\\fs781613 \\n\\\\hspace*{0.05cm} & 52$^0$ 33\\\\arcmin 28\\\\farcs23373 \\\\hspace*{0.05cm} \\\\\\\\ \\\\hline \\n{\\\\it Relative Sep. {\\\\bf (B-A)}} & $2\\\\fs1160588 $ \\n& $27\\\\farcs376325$ \\\\\\\\\\n{\\\\it Estimated error {\\\\bf (B-A)}} & $\\\\pm 0\\\\fs0000027$ & $ \\\\pm 0\\\\farcs000025$ \\\\\\\\ \\\\hline\\n\\\\end{tabular}\\n\\\\end{center}\\n\\\\label{tab3}\\n\\\\end{table*}\\n\\n\\n\\\\section{Comparison of astrometry at all 4 epochs} \\n\\nIn this section we make a comparison of the astrometric\\nmeasurements from the series of 4 epochs of observations.\\nAny increase of the temporal baseline in the program of monitoring the \\nseparation between A and B should result in a more precise \\nidentification of any systematic trends,\\nwith an improved elimination of random contributions.\\nIn Sect. 5.1 we justify comparing\\nthe astrometric values measured at the various epochs, even\\nthough non-identical observing, post-processing and analysis\\nprocedures were involved.\\nIn Sect. 5.2 we present the astrometric results from the 4 epochs.\\nIn Sects. 5.3, 5.4, 5.5 and 5.6 we present various analyses of these\\nresults, and attempt to quantify, or put upper-limits to,\\nproper motions within and between the A and B quasars.\\n\\n\\n\\\\subsection{Comparison between the techniques used at different epochs}\\n\\nBefore attempting a comparison of the astrometric results from \\nthe 4 observing epochs, we need to\\nshow that any bias in the astrometric estimates introduced by the\\nuse of different procedures is small compared with other errors in\\nthe measurements for the individual epochs.\\nThe consistency between the results from previous epochs of observations \\nhas been exhaustively tested (Marcaide et al. \\\\cite{marca94}; \\nRioja et al. \\\\cite{rioja97}).\\nWe outline here the largest changes involved in the fourth epoch, 1995.9,\\nwith respect to previous ones:\\n\\n\\\\begin{enumerate}\\n\\n\\\\item The observing array and frequency set-up used in the fourth epoch\\nwas different from previous epochs of observations \\n(frequency range 8404.5 to 8436.5 MHz instead of 8402.99 to 8430.99 MHz\\nat first 3 epochs). This results in a different coverage of the {\\\\it UV} \\nplane, leading to changes in the reconstruction of the source images. \\nInvestigations of such effects by Marcaide et al. (\\\\cite{marca94}) show that\\nthe effect on the astrometric anaylsis is only a few $\\\\mu$as. \\nIt is important to note that the observations at all 4 epochs have\\ncomparable resolutions and sample the same range of structural scales\\nin the sources.\\n\\n\\\\item The processing of the fourth epoch was done using the VLBA correlator,\\nwhich uses a theoretical model derived from CALC 8.2; we used AIPS to\\nanalyse the data with visibility phases residual to that model.\\nFor previous epochs the correlation was done at the MPIfR (Bonn) MK3\\ncorrelator, and an analysis of the data using total phases was made\\nwith VLBI3 (Robertson \\\\cite{robertson75}).\\nThe differences between CALC 8.2 and the one implemented in VLBI3 \\npropagate into changes of only 1-2~$\\\\mu$as in the astrometric analysis\\nof the 1038+528 A-B separation (Rioja \\\\cite{rioja93}, Rioja et al. \\n\\\\cite{rioja97}). \\nThis is because any such differences are ``diluted'' by the source \\nseparation expressed in radians - \\n$10^{-4}$ in the case of this very close source pair.\\n\\n\\\\item The values used in the analysis of previous epochs for\\nEarth Orientation Parameters (EOP), stations and reference source coordinates\\nwere consistently derived from a single global solution provided by Goddard \\nSpace Flight Center (GSFC). \\nFor the correlation of the fourth epoch, the values used for \\nEOP were derived from IERS solutions, and the station coordinates from \\nUSNO catalogs.\\nWe have made a comparison of the values derived for all the parameters at\\nthe 4 epochs from a single global solution from IERS (namely IERS eopc04),\\nwith the actual values\\nused in the individual epoch analysis. The difference between the corresponding\\nEOP values is always less than 4 mas. Such discrepancies propagate into \\nerrors in the relative position estimates at each epoch of only a few \\n$\\\\mu$as.\\n\\n\\\\item Our astrometric analysis in AIPS using a phase-referencing approach and\\nHDM differs from the phase difference method used in VLBI3 analysis.\\nComparisons show that these procedures are equivalent \\n(Porcas \\\\& Rioja \\\\cite{porcas96}; Thompson et al. \\\\cite{thompson86}).\\nBoth involve the definition of reference points in source maps;\\nuncertainties in the reference point positions \\n(as described in Sect. 4.3) arise in the same way.\\n\\n\\\\item Finally, a minor VLBA correlator error (Romney priv. comm.) caused\\nincorrect time labels to be attached to the visibility records, resulting in\\nincorrect ({\\\\it u,v}) values. \\nThe effect on the relative visibility phases for our source pair is small\\n($\\\\sim 0.004$\\\\degr) and can be neglected.\\n\\n\\\\end{enumerate}\\n\\n The magnitudes of all of the effects reported in this section are\\nmuch smaller than our estimate in Sect. 4.3 of the uncertainity in reproducing\\nthe reference point in the source, from epoch to epoch, and we are thus\\njustified in comparing the astrometric results from all 4 epochs.\\n\\n\\n\\\\subsection{Astrometric separations at the 4 epochs} \\n\\nThe astrometric measurements of the separations between the reference \\npoints in A and B at $\\\\lambda$ 3.6~cm from 4 epochs are presented in \\nFig.~\\\\ref{fig4}.\\nIt includes our new 1995.9 measurement and those from three earlier epochs, \\nin 1981.3, 1983.4 and 1990.5, reported in Marcaide \\\\& Shapiro \\n(\\\\cite{marca84}), Marcaide et al. (1994) and Rioja et al. (\\\\cite{rioja97}), \\nrespectively. The origin of the plot represents the separation at epoch 1.\\n\\n%%% FIGURE 4\\n\\n\\\\begin{figure}[h]\\n\\\\centerline{\\n{\\\\psfig{figure=fig4.ps,width=6.cm}}\\n}\\n\\\\caption{Measured separations between the A and B reference points at epochs\\n2 (1983.4), 3 (1990.5) and 4 (1995.9), with respect to epoch 1 (1981.2).\\nPlotted error bars correspond to $25~\\\\mu$as.\\n\\\\label{fig4}} \\n\\\\end{figure}\\n\\n\\nChanges with time in Fig.~\\\\ref{fig4} represent the vector difference between\\nany motions of the reference points in quasars A and B.\\nThe near-orthogonal nature of the source axes in 1038+52 A,B (along\\nwhich one might expect any motion to occur) simplifies the\\ninterpretation of any trends seen. The new 1995.9 value follows the\\nsame steady trend towards the NW shown by the three previous epochs.\\nRioja et al. (\\\\cite{rioja97}) interpreted this as an outward expansion of the\\nreference component in quasar B at a rate of $18~\\\\pm~5~\\\\mu$as~yr$^{-1}$, \\nand quoted an upper bound on any proper motion of quasar A of \\n$10~\\\\mu$as~yr$^{-1}$.\\n\\n\\\\subsection{Vector decomposition} \\n\\nIn this section we attempt to separate the individual contributions from \\nthe 2 quasars in the astrometric separation measurements presented in \\nFig.~\\\\ref{fig4}. We make no assumption about the stability of either \\ncomponent, but\\nassume that any displacements of the A or B reference points from their \\npositions at epoch 1 are along the corresponding source axis directions.\\nThis is a plausible assumption if the reference point coincides \\nwith a non-stationary component moving along a ballistic trajectory, \\nor with the location of the peak of brightness within an active core \\nor near the base of jet, where changes during episodes of activity are \\nlikely to occur along the jet direction.\\nThis approach is closely related to that used previously \\nby Rioja et al. (\\\\cite{rioja97}). For fixed assumed source axes for A and B,\\nit results in a unique decomposition of the changes in the A-B separation\\ninto separate A and B displacements, from 1981 to 1995.\\n\\nIt is clear that the dominant contribution to the separation changes\\nseen in Fig.~\\\\ref{fig4} comes from quasar B, \\nin which the source axis is well defined by the 127\\\\degr PA of\\nthe separation between core and reference components.\\nFor quasar A the source axis bends, from the inner ``core'' region \\n(PA = 15\\\\degr) to the outer jet components, and it is not so clear which \\ndirection should be chosen.\\n\\nIn our analysis we tried a range of values for fixing the A source axis \\n(0 to 45\\\\degr ~in steps of 5\\\\degr).\\nFor each, we calculated A and B reference-point displacements at epochs 2, \\n3 and 4 with respect to epoch 1.\\nThen we performed a least-squares fit to the B displacements with time to\\nestimate a linear expansion rate for the B reference feature along \\nPA 127\\\\degr. In Fig.~\\\\ref{fig5} we plot the deconvolved B reference point \\ndisplacements from the analysis with the A source axis fixed at \\nPA 25\\\\degr (the value adopted by Rioja et al. \\\\cite{rioja97}).\\nThe fitted expansion rate is $16.9~\\\\pm~0.6~\\\\mu$as~yr$^{-1}$;\\nthe error and associated rms values take account of the small number \\nof points and 2 degrees of freedom. This rate agrees well with the value\\nof $18~\\\\pm~5~\\\\mu$as~yr$^{-1}$ deduced by Rioja et al. (\\\\cite{rioja97}).\\nThe rms residual from the fit (7~$\\\\mu$as) is low, and vindicates\\nour use of measurements derived from differing techniques for\\ninvestigating the relative proper motion between A and B. \\n\\n%%% FIGURE 5\\n\\n\\\\begin{figure}[h]\\n\\\\centerline{\\n{\\\\psfig{figure=fig5.ps,width=6.cm}}\\n}\\n\\\\caption{Changes in position of reference component in B along PA 127\\\\degr,\\ndeduced from deconvolution of the A-B separation measurements. Assumed source\\naxis for A is 25\\\\degr.\\nPlotted error bars correspond to $25~\\\\mu$as.\\n\\\\label{fig5}} \\n\\\\end{figure}\\n\\n\\n\\\\subsection{Structural evolution within 1038+528 B} \\n\\nOur deconvolution analysis of the changes in separation measured between \\nall 4 epochs supports the finding, previously proposed, that the B reference\\ncomponent moves along the source axis, away from the B core.\\nIn this section we make an independent determination of the separation \\nrate between the core and reference component in B from measurements \\nwithin the maps at the 4 epochs.\\n\\nFig.~\\\\ref{fig6} shows the separation between the core and reference \\ncomponent in B at the four epochs plotted against time. For epochs 1--3 \\nwe used the values given in Rioja et al. (\\\\cite{rioja97}). For 1995.9 we \\nused AIPS task UVFIT to estimate a separation from the B visibility data \\ndirectly, in order to follow the methodology used for the other epochs as \\nclosely as possible; the value obtained was 1.895 mas.\\nThe slope from a least-squares fit corresponds to an expansion rate \\nof $13.0~\\\\pm~0.7~\\\\mu$as~yr$^{-1}$.\\nIn the standard picture of extragalactic radio sources, the ``core'' is\\nstationary, so this corresponds to an outward expansion of the\\nreference component along PA 127\\\\degr.\\n\\n%%% FIGURE 6\\n\\n\\\\begin{figure}[h]\\n\\\\centerline{\\n{\\\\psfig{figure=fig6.ps,width=6.cm}}\\n}\\n\\\\caption{Changes in the position of the reference component in B \\nalong PA 127\\\\degr, from measurements of its separation from the core\\nin hybrid maps of B.\\nPlotted error bars correspond to $25~\\\\mu$as.\\n\\\\label{fig6}} \\n\\\\end{figure}\\n\\n\\nThe rms of the fit (8~$\\\\mu$as) is again surprisingly low, implying\\ntypical errors in the separation measurements at each epoch \\n(both within the B structure and between the reference points)\\nof only about 10--12$~\\\\mu$as along the direction of the B source axis.\\nThis is considerably less than the estimate of position separation \\nerrors given in Sect. 4.3. \\n\\n\\\\subsection{Relative proper motion }\\n\\nThe analysis presented in the previous sections demonstrate\\nclearly that the chosen reference component within quasar B is\\nunsuitable for use as a marker for tracing any relative proper motion\\nbetween quasars A and B. The value of its expansion velocity derived \\nin Sect. 5.4 appears to differ significantly from that deduced by \\nvector-decomposition in Sect. 5.3. Although the difference between \\nthese estimates, if real, could be interpreted as motion of the core of B \\nat a rate of $\\\\sim 4~\\\\mu$as~yr$^{-1}$, this is not a conclusive result\\nsince differences of this order arise from choosing different values of \\nPA for the motion in A in the vector decomposition method.\\n\\nA more suitable tracer of relative proper motion between the quasars is \\nthe variation of the separation between the cores of A and B.\\nWe have used the separations between the core and reference component\\nmeasured in the B map at each epoch, and the astrometric\\nseparations between A and B, to calculate the separations between the\\nA and B cores at each epoch; these are plotted in Fig.~\\\\ref{fig7}.\\nThe area occupied by the points defines an upper limit of \\n$\\\\sim 10~\\\\mu$as~yr$^{-1}$ for any relative proper motion between \\nthe A and B cores, and hence between the quasars themselves, during\\nthe period of nearly 15 years for which the separation has been\\nmonitored with VLBI.\\nThe limit seems to be set by the relatively large deviation of the\\n1995.9 epoch point in the direction of the A source axis, presumably\\narising from the difficulty in defining the reference point at the\\nA ``core'' from epoch to epoch. \\n\\n%%% FIGURE 7\\n\\n\\\\begin{figure}[h]\\n\\\\centerline{\\n{\\\\psfig{figure=fig7.ps,width=6.cm}}\\n}\\n\\\\caption{Separation between the cores of A and B (with respect to epoch 1),\\nderived by correcting the A-B reference point separation measurements with the\\ncore-reference separations measured in the B hybrid maps.\\nPlotted error bars correspond to $25~\\\\mu$as.\\n\\\\label{fig7}} \\n\\\\end{figure}\\n\\n\\n\\\\subsection{Possible ``core'' motions ? } \\n\\nFinally, we investigate any possible residual motions of the ``cores'' \\nin A and B. The most likely causes of any such apparent motions are \\nchanges in the relative brightness or positions of features in the \\nsource structures at a resolution below that of the maps.\\nOne might expect that these, too, would produce effects predominantly\\nalong the source axis directions.\\nWe therefore used the vector deconvolution method on the plot of\\ncore-core separation with time to study displacements of the cores\\nalong their source axis directions.\\nFig.~\\\\ref{fig8}a and b show plots of the separated contributions from \\nB and A, for an assumed A source axis PA 25\\\\degr.\\nThe displacements for the B core seem to increase systematically.\\nThe fitted rate is $3.8~\\\\pm~0.3~\\\\mu$as~yr$^{-1}$, indicating a possible \\nslow outward motion. The displacements for the A core do not seem to \\nvary systematically - the fitted slope is $5.5~\\\\pm~3.6~\\\\mu$as~yr$^{-1}$.\\nHere the scatter is considerably larger, reflecting both the difficulties of\\ndefining the reference point along the A core-jet axis, and\\nalso, perhaps, real ``jitter'' of the position of the peak due to variations \\nin the ``core'' substructure. These plots indicate the level of stability \\nof the individual core positions; the fits represent realistic upper limits \\nto any possible systematic core motion in the A and B quasars along their \\nsource axis directions.\\n\\n%%% FIGURE 8\\n\\n\\\\begin{figure*}\\n\\\\centerline{\\n{\\\\psfig{figure=fig8a.ps,width=6.cm}}\\n\\\\put (-140,140) {\\\\bf {a)}}\\n{\\\\psfig{figure=fig8b.ps,width=6.cm}}\\n\\\\put (-130,140) {\\\\bf {b)}}\\n}\\n\\\\caption{Residual motions of the cores using the deconvolution approach.\\n {\\\\bf a} Displacements of B core along PA 127\\\\degr; \\n{\\\\bf b} Displacements of A core along PA 25\\\\degr. \\nPlotted error bars correspond to $25~\\\\mu$as.\\n\\\\label{fig8}} \\n\\\\end{figure*}\\n\\n\\n\\\\section{Conclusions} \\n\\nThe series of astrometric VLBI measurements of the separation between \\nthe quasar pair 1038+528 A and B, spanning\\nnearly 15 years, provides excellent material for investigating \\nthe relative proper motion of two extragalactic radio sources and\\nthe positional stability of their cores.\\nThe changes measured in the separations between quasars A and B \\nat 3.6~cm are dominated by the motion of the reference feature in quasar B. \\nThese astrometric results, and measurements in the hybrid maps of B are\\ncompatible with an expansion rate for the B reference component of \\n13--17$~\\\\mu$as~yr$^{-1}$.\\nAt a redshift of 2.296 this translates to an apparent\\ntransverse velocity of 0.55--0.70~c~h$^{-1}$.\\nWe note that this is an order of magnitude smaller than the more\\ntypical superluminal velocities seen in many quasars; it is a \\nrare example of a subluminal velocity measured for a knot in a quasar jet.\\n\\nAfter correcting for the motion of the reference component in B,\\nwe can put a conservative upper bound to any relative proper\\nmotion between the quasars of $10~\\\\mu$as~yr$^{-1}$.\\nDespite the increase in temporal baseline, this upper bound is no\\nbetter than that given by Rioja et al. (\\\\cite{rioja97}).\\nIts value is related to the difficulty in reproducing a stable reference\\nposition along the A source axis near its ``core''.\\n\\nTheories in which the redshifts of quasars do not indicate cosmological\\ndistances, and in which quasars are ``local'' and have high Doppler\\nredshifts (e.g. Narlikar \\\\& Subramanian \\\\cite{narlikar83}) are incompatible \\nwith our measured upper-limit to relative proper motion. Quasars at \\n100 Mpc distance moving at relativistic speeds would have proper motions \\nof the order of $600~\\\\mu$as~yr$^{-1}$, nearly 2 orders of magnitude \\ngreater than our limit. Assuming cosmological distances,\\nour limit corresponds to apparent transverse velocities of \\n0.43~c~h$^{-1}$ and 0.22~c~h$^{-1}$ at the redshifts of the B and A\\nquasars, respectively.\\n\\nWe have investigated the way in which the definition of \\nreference points in a map may be only loosely ``fixed'' to the radio\\nsource structure, especially when the latter is strongly asymmetric.\\nWe have also developed an alternative analysis route - Hybrid Double\\nMapping - for imaging both sources of a close pair simultaneously, and\\nat the same time preserving their relative astrometric information\\nin a single map.\\n\\nThe surprisingly low rms from the fits of linear expansion in quasar B,\\nand the discrepancy between the two estimates \\n($16.9~\\\\pm~0.6~\\\\mu$as~yr$^{-1}$ from the astrometric measurements and\\n $ 13.0~\\\\pm~0.7~\\\\mu$as~yr$^{-1}$ from the hybrid maps)\\nare suggestive of (but do not prove) a residual motion of the core \\nin quasar B; our decomposition along the source axis direction gives a fit\\nof $3.8~\\\\pm~0.3~\\\\mu$as~yr$^{-1}$, corresponding to an apparent transverse \\nvelocity of 0.17~c~h$^{-1}$. If real, this might indicate a steady change \\nin physical conditions at the base of the jet, or perhaps the emergence \\nof a new knot component moving outwards with a velocity similar to the \\nreference component, but as yet unresolved by our 0.5 mas beam.\\nIn this regard, it is interesting to note the slight extension of\\nthe core of quasar B in PA 132\\\\degr given by the Gaussian model fit.\\n\\nThe low rms derived from fits to the expansion of the B reference component \\nindicate that we have been overly conservative in our estimate of \\n$18~\\\\mu$as for the error in reference point positions. Errors at least \\n2 times smaller are implied, corresponding to a sixtieth of the beamwidth. \\nIt is interesting to note that such small errors are also implied in the \\nwork of Owsianik \\\\& Conway (\\\\cite{owsianik98}), where the low scatter in \\nthe plot of expansion of the CSO source \\\\object{0710+439} allows an \\nexpansion rate of $14.1~\\\\pm~1.6~\\\\mu$as~yr$^{-1}$ to be determined.\\n\\nThere are no obvious systematic motions within quasar A, but the ``noise'' \\nin the estimates of position along its axis are much larger.\\nThis noise, along with any associated underlying changes in source\\nsubstructure, provides a fundamental limit to estimates of\\nany systematic core motion in A. Improvements on the estimates of (or upper\\nbounds to) the relative motion between the quasars, or of the\\nindividual motion of the A core, will require a considerable\\nincrease in the temporal baseline of VLBI monitoring.\\n\\n\\\\newpage\\n\\n\\\\appendix \\n\\n\\\\section {Hybrid Double Mappping (HDM)}\\n\\n\\n{\\\\bf A.1 Principle of Hybrid Double Mapping} \\\\\\\\\\n\\n\\\\noindent\\nThe visibility function, $V$, measured at time $t$, on a baseline between\\nantennas $i$ and $j$, is represented by a complex function with amplitude $A$, \\nphase $P$:\\n\\n\\\\[ V(i,j) = A * e^{i[\\\\phi]}(t) \\\\]\\n\\n\\\\noindent\\nFor this analysis it is convenient to indentify 3 contributions to\\nthe visibility phase:\\n\\n\\\\[ \\\\phi(i,j) = \\\\phi_{s}(u,v) + \\\\phi_{p}(u,v) + \\\\phi_{m}(t) \\\\]\\n\\n\\\\noindent\\nwhere \\n\\n\\\\begin{description} \\n\\\\item [$\\\\phi_s$] is due to source structure, evaluated w.r.t. a reference\\nposition for the source. \\\\\\\\\\n\\n \\\\item [$\\\\phi_p$] is due to any offset of the \\ntrue source position from the reference position. \\\\\\\\\\n\\nBoth $\\\\phi_s$ and \\n$\\\\phi_p$ are functions of the resolution coordinates, $u$ and $v$, at time \\n$t$. \\\\\\\\\\n\\n\\\\item [$\\\\phi_m$] is due to inaccuracies in the correlator model calculation of\\n the interferometer geometry and the signal propagation delays\\n in the ionosphere, troposphere and receiving system; it is an \\n unknown function of time. \\\\\\\\\\n This term can be represented by the difference of two\\n ''antenna-based'' phases, $\\\\theta_i$ and $\\\\theta_j$, since it can \\n be related to the \\n difference in signal arrival times at the two sites.\\n (This analysis is a simplification which ignores possible\\n ''non-closing'' instrumental baseline phase terms arising from\\n e.g. un-matched bandpasses and polarisation impurities.) \\n\\\\end{description}\\n\\n\\\\[ \\\\phi(i,j) = \\\\phi_s(u,v) + \\\\phi_p(u,v) + \\\\theta_i(t) - \\\\theta_j(t) \\\\]\\n\\n\\\\noindent\\nIn conventional hybrid mapping, an iterative procedure is used\\nto separate out the antenna-based phase terms from the ''source'' terms;\\nthe latter must produce a consistent and physically plausible source\\nstructure after Fourier transformation of the corrected visibility:\\n\\n\\\\[ \\\\underbrace {A * e^{i[\\\\phi_s+\\\\phi_p]}(u,v)}_{corrected \\\\: visibility} = \\nV(i,j) * \\\\underbrace {e^{-i[\\\\theta_i(t)-\\\\theta_j(t)]}}_{antenna \\\\: phase \\\\: terms} \\\\] \\n\\n\\\\noindent\\nHowever, the position offset term, $\\\\phi_p$, can also be expressed as a difference \\nin wavefront arrival times at the 2 antennas and so it is also\\n''absorbed'' in antenna phase terms $\\\\theta_i'$, $\\\\theta_j'$; \\nthe ''absolute'' position information is lost:\\n\\n\\\\[ \\\\underbrace {A * e^{i[\\\\phi_s]}(u,v)}_{corrected \\\\: visibility} = \\nV(i,j) * \\\\underbrace {e^{-i[\\\\theta_i'(t)-\\\\theta_j'(t)]}}_{antenna \\\\: phase\\n\\\\: terms} \\\\]\\n\\n\\\\noindent\\nIn Hybrid Double Mapping (HDM), the visibility functions of two \\nsources observed simultaneously are added. For a close source pair, we \\nmake the same assumption as for conventional phase-referencing - that the \\nmodel error phase terms are essentially the same for both sources. We make \\na further assumption that the $u,v$ coordinates are also essentially the same\\nfor both sources, for each baseline and time. The visibility sum, $V^1 + V^2$,\\ncan then be re-written: \\\\\\\\\\n\\n\\n\\\\[ \\\\underbrace {(A^1 * e^{i[\\\\phi^1_{s}]} + A^2 * e^{i[\\\\phi^2_{s}+(\\\\phi^2_{p}\\n-\\\\phi^1_{p})]})(u,v)}_{corrected \\\\: visibility \\\\: sum} = \\\\]\\n\\\\[ \\\\;\\\\;\\\\; \\\\vspace*{2cm} = V^{sum}(i,j) * \\\\underbrace {e^{-i[\\\\theta_i'(t)-\\\\theta_j'(t)]}}_{antenna \\\\:\\n phase \\\\: terms} \\\\] \\n\\n\\n%\\\\begin{eqnarray*}\\n%\\\\lefteqn{ \\\\[ \\\\underbrace {(A_1e^{i[\\\\phi_{1s}]}+A_2e^{i[\\\\phi_{2s}+(\\\\phi_{2p}-\\\\phi_{1p})]})(u,v)}_{corrected \\\\: visibility \\\\: sum} = } \\\\\\\\\\n%& & V^{sum}(i,j) * \\\\underbrace {e^{-i[\\\\theta_i'(t)-\\\\theta_j'(t)]}}_{antenna \\\\:\\n%phase \\\\: terms} \\\\] \\n%\\\\end{eqnarray*}\\n\\n\\\\noindent\\nThis may be recognised as the visibility function of a ''composite''\\nsource consisting of the sum of the brightness distributions of sources\\n1 and 2, with antenna-based phase error terms $\\\\theta_i'$, $\\\\theta_j'$, \\nas before.\\nThe HDM method consists of performing the normal hybrid mapping\\nprocedure with the visibility sum, resulting in the separation of the\\nantenna-based errors, and a physically plausible map of the sum of\\nthe two source brightness distrubutions. An important point is that,\\nwhereas the {\\\\it origin} of the map of the composite source is arbitrary (as\\nit depends on the position of the starting model), the {\\\\it separation} of\\nthe two source brightness distributions within the composite map\\n(determined by $\\\\phi^2_{p}-\\\\phi^1_{p}$) is fixed during the phase \\nseparation procedure,\\nand is equal to the {\\\\it difference} of the errors in the two source\\npositions used for correlation. We call this the ''residual separation''. \\\\\\\\\\n\\n\\\\noindent\\n{\\\\bf A.2 Practical aspects} \\\\\\\\\\n\\n\\\\noindent\\nThere are some practical aspects to be considered. If the source\\ncoordinates used in the correlator model are very precise, then the\\nresidual separation may be less than the interferometer beamwidth, and\\nthe two source distributions will lie on top of each other. \\nIn this case it is desireable to\\nintroduce an artificial position offset into one of the\\nsource visibility functions before forming the visibility sum, to\\nensure that the two source reference features are well separated in the\\nHDM map. One should also arrange that the peak of one source\\ndoes not lie on the sidelobe response of the other in the \\\"dirty\\\" map,\\nas this may degrade the CLEAN deconvolution process in the mapping step.\\\\\\\\\\n\\n\\\\noindent\\n Another important consideration is that the time-averaged samples\\nof the summed visibility function contain equal contributions from both\\nsource visibility functions. When both sources are observed\\nsimultaneously this will normally be the case, except when different\\namounts of data are lost in the two separate correlator passes needed\\nfor the two source positions. It is important to edit the data sets\\ncarefully to fulfil this condition. \\\\\\\\\\n\\n\\\\noindent\\n The range of validity of the assumption that the $(u,v)$\\ncoordinates for the two sources are the same depends on the ''dilution\\nfactor'', i.e. the reciprocal of the source separation, measured in\\nradians. The $(u,v)$ value assigned to the summed visibility will be\\nincorrect for either source by roughly 1 part in the dilution factor\\n(roughly 1 in 6000 for 1038+528A,B). \\nThis is equivalent to having source visibility phase errors of this\\norder, and thus limits the size of an HDM map to be less than the\\nbeamwidth times the dilution factor; the residual separation should be\\nmuch smaller than this value.\\\\\\\\\\n\\n\\\\noindent\\nIn the actual analysis used in this work, we first made a rough \\ncorrection to the phase of the summed visibility of 1038+528 A + B, using\\nthe antenna phase and phase derivative errors from fringe-fitting\\n1038+528A using a point source model. However, there is no reason why\\none should not fringe-fit the summed visibility function directly. \\\\\\\\\\n\\n\\\\noindent\\n{\\\\bf A.3 Applications} \\\\\\\\\\n\\n\\\\noindent\\nThe HDM method can in principle be applied\\nwhenever two (or more !) radio sources are observed simultaneously,\\nbut are correlated at separate field centres; however, \\nthey must be close enough so that the conditions of same $(u,v)$\\ncoverage and same correlator model errors apply.\\nThe method uses the structures of BOTH sources simultaneously to\\nseparate out the antenna phase errors, as opposed to a single source in \\nsimple hybrid mapping.\\nIf both sources are strong (as with 1038+528 A and B),\\nconstraining the (single) antenna phase solutions with two structures\\nshould lead to a more rigorous and robust separation between the\\nsource and antenna phase terms.\\nOne field of application is in high resolution VLBI imaging of\\ngravitational lens systems with wide image separations (e.g. \\nimages A and B of QSO 0957+561 with 6.1 arcsec separation)\\nwhere preserving the necessary wide field-of-view from a single \\ncorrelation may result in inconveniently large data sets.\\nWhen one source is very weak, however,\\nthere is probably little to be gained over normal hybrid mapping. \\\\\\\\\\n\\n\\\\noindent\\nFor relative astrometry studies (as described in this paper),\\nthe HDM method has some advantages over conventional phase-reference \\nmapping and explicit phase-differencing methods.\\nIn phase-differencing astrometry, separate hybrid maps must be made of\\nboth sources to correct for source structural phase terms and \\nthe antenna phase errors are NOT constrained to be the same. Imperfect \\nseparation between source and antenna phase terms can increase the noise \\non the differenced phase, as well as lead to possible systematic errors.\\nIn phase-reference astrometry, only one of the sources is used to solve\\nfor the antenna phase terms; imperfect separation can lead to extra\\nphase noise in the phase-referenced visibility of the ''target'' source.\\nIn HDM we use both source\\nstructures simultaneously to separate the (common) antenna error\\nphases from that of a single \\\"structure\\\" in which the \\nreference points of the two sources are spaced by the residual separation.\\\\\\\\\\n\\n\\\\noindent\\nWhen the separation between the two sources of a pair exceeds\\nthe telescope primary beamwidths, astrometric and phase-reference \\nobservations \\nmust involve switching between the sources, and the visibility phase of at \\nleast one of the sources must normally be interpolated in the observing gap. \\nThe condition that must be fulfilled for HDM to work in\\nthis case is that an equal number of observations of both sources must\\nbe added to form an average visibility function for the length of the\\n''solution interval'' in the phase self-calibration step of HDM.\\nThis length is generally limited by the coherence time of the\\natmosphere, and would imply a very fast switching cycle in most cases.\\nAnother application for HDM could be in the the analysis of\\n''cluster-cluster'' VLBI (see e.g. Rioja et al. \\\\cite{rioja97b}), \\nin which two or more sources are observed simultaneously on VLBI baselines \\nby using more than one telescope at each site.\\n\\n\\n\\\\begin{acknowledgements}\\n\\nWe thank Dave Graham for help with the observations in Effelsberg,\\nTony Beasley for asistance at the VLBA, and Mark Reid for useful comments\\non the text. M.J.R. wishes to acknowledge support for this research by the\\nEuropean Union under contract CHGECT920011.\\nThe National Radio Astronomy Observatory is a facility\\nof the National Science Foundation operated under cooperative\\nagreement by Associated Universities, Inc.\\n\\n\\\\end{acknowledgements}\\n\\n\\\\begin{thebibliography}{}\\n\\n\\\\bibitem[1988]{alef88} Alef W.A., 1988, in Proc. IAU Symp. 129, \\ned. Reid M., Moran J., Kluwer, p. \\\\ 523 \\n\\n\\\\bibitem[1995]{beasley95} Beasley A.J., Conway J.E., 1995, \\nVery Long Baseline Interferometry and the VLBA, eds. Zensus J.A., \\nDiamond P.J., Napier P.J., ASP Conference Series, Vol. 82, p. \\\\ 327.\\n\\n\\\\bibitem[1986]{blandford86} Blandford R.D., K\\\\\\\"onigl A., 1986, \\nApJ 308, 83\\n\\n\\\\bibitem[1983]{marca83} Marcaide J.M., Shapiro I.I., 1983, AJ 88, 1133 \\n\\\\bibitem[1984]{marca84} Marcaide J.M., Shapiro I.I., 1984, ApJ 276, 56\\n\\\\bibitem[1994]{marca94} Marcaide J.M., El\\\\'{o}segui P., Shapiro I.I., 1994, \\n AJ 108, 368 \\n\\\\bibitem[1983]{narlikar83} Narlikar J.V., Subramanian K., 1983, \\nApJ 273, 44\\n\\\\bibitem[1978]{owen78} Owen F.N., Porcas R.W., Neff S.G., 1978, \\nAJ 83, 1009\\n\\\\bibitem[1980]{owen80} Owen F.N., Wills B.J., Wills D., 1980, ApJ 235, L57\\n\\\\bibitem[1998]{owsianik98} Owsianik I., Conway J.E., 1998, A\\\\&A 337, 69\\n\\\\bibitem[1986]{porcas87} Porcas R.W., 1987, Superluminal Radio Sources, ed.\\n Zensus A., Pearson A., Cambridge University Press, p. \\\\ 12\\n\\\\bibitem[1996]{porcas96} Porcas R.W., Rioja M.J., 1996, Proc. of the 11th \\nWorking Meeting on European VLBI for Geodesy and Astrometry, Ed. Elgered\\nG., p. \\\\ 209\\n\\\\bibitem[1993]{rioja93} Rioja M.J., 1993, PhD. Thesis, Universidad de Granada\\n\\\\bibitem[1997]{rioja97} Rioja M.J., Marcaide J.M., El\\\\'osegui P., \\nShapiro I.I., 1997, A\\\\&A 325, 383 \\n\\\\bibitem[1997]{rioja97b} Rioja M.J., Stevens E.,\\nGurvits L., et al., 1997, {\\\\it Vistas in Astronomy} 41 (2), 213 \\n%\\\\bibitem[2000]{rioja00} Rioja, M.J., Porcas, R.W., 2000, {\\\\it in preparation}\\n\\\\bibitem[1975]{robertson75} Robertson D.S., 1975, PhD Thesis, MIT\\n%\\\\bibitem[1996]{romney96} Romney, J.D., 1996, (VLBA email memorandum \\n%of 14 March) \\n\\\\bibitem[1986]{thompson86} Thompson A.R., Moran J.M., Swenson G.W., 1986, \\nInterferometry and Synthesis in Radio Astronomy. Wiley-Interscience, \\nNew York, p. 400\\n\\n\\\\end{thebibliography}{}\\n\\n\\n\\n\\n\\\\end{document}\\n\\n\"\n }\n]","isConversational":false},"bibtex":{"kind":"list like","value":[{"name":"astro-ph0002097.extracted_bib","string":"\\begin{thebibliography}{}\n\n\\bibitem[1988]{alef88} Alef W.A., 1988, in Proc. IAU Symp. 129, \ned. Reid M., Moran J., Kluwer, p. \\ 523 \n\n\\bibitem[1995]{beasley95} Beasley A.J., Conway J.E., 1995, \nVery Long Baseline Interferometry and the VLBA, eds. Zensus J.A., \nDiamond P.J., Napier P.J., ASP Conference Series, Vol. 82, p. \\ 327.\n\n\\bibitem[1986]{blandford86} Blandford R.D., K\\\"onigl A., 1986, \nApJ 308, 83\n\n\\bibitem[1983]{marca83} Marcaide J.M., Shapiro I.I., 1983, AJ 88, 1133 \n\\bibitem[1984]{marca84} Marcaide J.M., Shapiro I.I., 1984, ApJ 276, 56\n\\bibitem[1994]{marca94} Marcaide J.M., El\\'{o}segui P., Shapiro I.I., 1994, \n AJ 108, 368 \n\\bibitem[1983]{narlikar83} Narlikar J.V., Subramanian K., 1983, \nApJ 273, 44\n\\bibitem[1978]{owen78} Owen F.N., Porcas R.W., Neff S.G., 1978, \nAJ 83, 1009\n\\bibitem[1980]{owen80} Owen F.N., Wills B.J., Wills D., 1980, ApJ 235, L57\n\\bibitem[1998]{owsianik98} Owsianik I., Conway J.E., 1998, A\\&A 337, 69\n\\bibitem[1986]{porcas87} Porcas R.W., 1987, Superluminal Radio Sources, ed.\n Zensus A., Pearson A., Cambridge University Press, p. \\ 12\n\\bibitem[1996]{porcas96} Porcas R.W., Rioja M.J., 1996, Proc. of the 11th \nWorking Meeting on European VLBI for Geodesy and Astrometry, Ed. Elgered\nG., p. \\ 209\n\\bibitem[1993]{rioja93} Rioja M.J., 1993, PhD. Thesis, Universidad de Granada\n\\bibitem[1997]{rioja97} Rioja M.J., Marcaide J.M., El\\'osegui P., \nShapiro I.I., 1997, A\\&A 325, 383 \n\\bibitem[1997]{rioja97b} Rioja M.J., Stevens E.,\nGurvits L., et al., 1997, {\\it Vistas in Astronomy} 41 (2), 213 \n%\\bibitem[2000]{rioja00} Rioja, M.J., Porcas, R.W., 2000, {\\it in preparation}\n\\bibitem[1975]{robertson75} Robertson D.S., 1975, PhD Thesis, MIT\n%\\bibitem[1996]{romney96} Romney, J.D., 1996, (VLBA email memorandum \n%of 14 March) \n\\bibitem[1986]{thompson86} Thompson A.R., Moran J.M., Swenson G.W., 1986, \nInterferometry and Synthesis in Radio Astronomy. Wiley-Interscience, \nNew York, p. 400\n\n\\end{thebibliography}"}],"string":"[\n {\n \"name\": \"astro-ph0002097.extracted_bib\",\n \"string\": \"\\\\begin{thebibliography}{}\\n\\n\\\\bibitem[1988]{alef88} Alef W.A., 1988, in Proc. IAU Symp. 129, \\ned. Reid M., Moran J., Kluwer, p. \\\\ 523 \\n\\n\\\\bibitem[1995]{beasley95} Beasley A.J., Conway J.E., 1995, \\nVery Long Baseline Interferometry and the VLBA, eds. Zensus J.A., \\nDiamond P.J., Napier P.J., ASP Conference Series, Vol. 82, p. \\\\ 327.\\n\\n\\\\bibitem[1986]{blandford86} Blandford R.D., K\\\\\\\"onigl A., 1986, \\nApJ 308, 83\\n\\n\\\\bibitem[1983]{marca83} Marcaide J.M., Shapiro I.I., 1983, AJ 88, 1133 \\n\\\\bibitem[1984]{marca84} Marcaide J.M., Shapiro I.I., 1984, ApJ 276, 56\\n\\\\bibitem[1994]{marca94} Marcaide J.M., El\\\\'{o}segui P., Shapiro I.I., 1994, \\n AJ 108, 368 \\n\\\\bibitem[1983]{narlikar83} Narlikar J.V., Subramanian K., 1983, \\nApJ 273, 44\\n\\\\bibitem[1978]{owen78} Owen F.N., Porcas R.W., Neff S.G., 1978, \\nAJ 83, 1009\\n\\\\bibitem[1980]{owen80} Owen F.N., Wills B.J., Wills D., 1980, ApJ 235, L57\\n\\\\bibitem[1998]{owsianik98} Owsianik I., Conway J.E., 1998, A\\\\&A 337, 69\\n\\\\bibitem[1986]{porcas87} Porcas R.W., 1987, Superluminal Radio Sources, ed.\\n Zensus A., Pearson A., Cambridge University Press, p. \\\\ 12\\n\\\\bibitem[1996]{porcas96} Porcas R.W., Rioja M.J., 1996, Proc. of the 11th \\nWorking Meeting on European VLBI for Geodesy and Astrometry, Ed. Elgered\\nG., p. \\\\ 209\\n\\\\bibitem[1993]{rioja93} Rioja M.J., 1993, PhD. Thesis, Universidad de Granada\\n\\\\bibitem[1997]{rioja97} Rioja M.J., Marcaide J.M., El\\\\'osegui P., \\nShapiro I.I., 1997, A\\\\&A 325, 383 \\n\\\\bibitem[1997]{rioja97b} Rioja M.J., Stevens E.,\\nGurvits L., et al., 1997, {\\\\it Vistas in Astronomy} 41 (2), 213 \\n%\\\\bibitem[2000]{rioja00} Rioja, M.J., Porcas, R.W., 2000, {\\\\it in preparation}\\n\\\\bibitem[1975]{robertson75} Robertson D.S., 1975, PhD Thesis, MIT\\n%\\\\bibitem[1996]{romney96} Romney, J.D., 1996, (VLBA email memorandum \\n%of 14 March) \\n\\\\bibitem[1986]{thompson86} Thompson A.R., Moran J.M., Swenson G.W., 1986, \\nInterferometry and Synthesis in Radio Astronomy. Wiley-Interscience, \\nNew York, p. 400\\n\\n\\\\end{thebibliography}\"\n }\n]","isConversational":false}}},{"rowIdx":97,"cells":{"paper_id":{"kind":"string","value":"astro-ph0002098"},"title":{"kind":"string","value":"Chemistry in the Envelopes around Massive Young Stars"},"authors":{"kind":"list like","value":[{"author":"Ewine F.\\ van Dishoeck and Floris F.S.\\ van der Tak"}],"string":"[\n {\n \"author\": \"Ewine F.\\\\ van Dishoeck and Floris F.S.\\\\ van der Tak\"\n }\n]","isConversational":false},"abstract":{"kind":"string","value":"Recent observational studies of intermediate- and high-mass star-forming regions at submillimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components associated with young stellar objects are summarized. Procedures for determining the temperature, density and abundance profiles in the envelopes are outlined. A detailed study of a set of infrared-bright massive young stars reveals systematic increases in the gas/solid ratios, the abundances of evaporated molecules, and the fraction of heated ices with increasing temperature. Since these diverse phenomena involve a range of temperatures from $<100\\,$K to 1000~K, the enhanced temperatures must be communicated to both the inner and outer parts of the envelopes. This `global heating' plausibly results from the gradual dispersion of the envelopes with time. Similarities and differences with low-mass YSOs are discussed. The availability of accurate physical models will allow chemical models of ice evaporation followed by `hot core' chemistry to be tested in detail."},"latex":{"kind":"list like","value":[{"name":"dishoeck.tex","string":"% SAMPLE1.TEX -- WGAS sample paper with minimal markup.\n\n% Lines starting with \"%\" are comments; they will be ignored by LaTeX.\n\n\\documentstyle[11pt,newpasp,psfig,epsf,twoside]{article}\n\\def\\gtsim{{_>\\atop{^\\sim}}}\n\\def\\ltsim{{_<\\atop{^\\sim}}}\n\n\\begin{document}\n\n\\title{Chemistry in the Envelopes around Massive Young Stars}\n\\author{Ewine F.\\ van Dishoeck and Floris F.S.\\ van der Tak}\n\\affil{Leiden Observatory, P.O.\\ Box 9513, 2300 RA Leiden,\nThe Netherlands}\n\n\\begin{abstract}\nRecent observational studies of intermediate- and high-mass\n star-forming regions at submillimeter and infrared wavelengths are\n reviewed, and chemical diagnostics of the different physical\n components associated with young stellar objects are summarized.\n Procedures for determining the temperature, density and abundance\n profiles in the envelopes are outlined. A detailed study of a set of\n infrared-bright massive young stars reveals systematic increases in\n the gas/solid ratios, the abundances of evaporated molecules, and the\n fraction of heated ices with increasing temperature. Since these\n diverse phenomena involve a range of temperatures from $<100\\,$K to\n 1000~K, the enhanced temperatures must be communicated to both the\n inner and outer parts of the envelopes. This `global heating'\n plausibly results from the gradual dispersion of the envelopes with\n time. Similarities and differences with low-mass YSOs are discussed.\n The availability of accurate physical models will allow chemical\n models of ice evaporation followed by `hot core' chemistry to be\n tested in detail.\n\n\n\\end{abstract}\n\n\n%% Keywords: High-mass star formation, ices, hot cores, envelopes\n%% \n%% Objects: Orion-KL, Orion-IRc2, SGrB2, W~3 IRS5, W~3(H$_2$O), AFGL 2591,\n%% AFGL 2136, NGC 7538 IRS9, W~33A, G34.3, S 140, W~3 IRS4\n%% Molecules: CO, C$^{17}$O, CS, H$_2$CO, HC$_5$N, H$_2$O, CO$_2$,\n%% CH$_3$OH, CH$_3$OCH$_3$, CH$_3$CN, C$_2$H$_2$, S~I, PAHs\n%% OH, SiO, SO$_2$, CN, HCN, C~II, CO$^+$\n\n\\section{Introduction}\n\nMassive star-forming regions have traditionally been prime targets for\nastrochemistry owing to their bright molecular lines (e.g., Johansson\net al.\\ 1984, Cummins et al.\\ 1986, Irvine et al.\\ 1987, Ohishi 1997).\nMassive young stellar objects (YSOs) have luminosities of $\\sim 10^4 -\n10^6$ L$_\\odot$ and involve young O- and B-type stars. Because their\nformation proceeds more rapidly than that of low-mass stars and\ninvolves ionizing radiation, substantial chemical differences may be\nexpected. The formation of high mass stars is much less well\nunderstood than that of low-mass stars. For\nexample, observational phenomena such as ultracompact H II regions,\nhot cores, masers and outflows have not yet been linked into a single\nevolutionary picture. Chemistry may well be an important diagnostic\ntool in establishing such a sequence.\n \nMost of the early work on massive star-forming regions has centered on\ntwo sources, Orion--KL and SgrB2. Numerous line surveys at millimeter\n(e.g., Blake et al.\\ 1987, Turner 1991) and submillimeter (Jewell et\nal.\\ 1989, Sutton et al.\\ 1991, 1995, Schilke et al.\\ 1997)\nwavelengths have led to an extensive inventory of molecules through\nidentification of thousands of lines. In addition, the surveys have\nshown strong chemical variations between different sources.\n\nIn recent years, new observational tools have allowed a more detailed and\nsystematic study of the envelopes of massive YSOs. Submillimeter observations\nroutinely sample smaller beams (typically 15$''$ vs.\\ 30$''$--1$'$ ) and\nhigher critical densities ($\\geq 10^6$ vs.\\ $10^4$ cm$^{-3}$) than the earlier\nwork. Moreover, interferometers at 3 and 1 millimeter provide maps with\nresolutions of $0.5''$--5$''$. Finally, ground- and space-based infrared\nobservations allow both the gas and the ices to be sampled (e.g., Evans et\nal.\\ 1991, van Dishoeck et al.\\ 1999). These observational developments have\nled to a revival of the study of massive star formation within the last few\nyears. Recent overviews of the physical aspects of high-mass star formation\nare found in Churchwell (1999) and Garay \\& Lizano (1999).\n\n\nIn this brief review, we will first summarize available observational\ndiagnostics to study the different phases and physical components\nassociated with massive star formation. Subsequently, an overview of\nrecent results on intermediate mass YSOs is given, which are often\nbetter characterized than their high-mass counterparts because of\ntheir closer distance. Subsequently, we will discuss a specific sample\nof embedded massive YSOs which have been studied through a combination\nof infrared and submillimeter data. After illustrating\nthe modeling techniques, we address the question how the\nobserved chemical variations are related to evolutionary effects,\ndifferent conditions in the envelope (e.g., $T$, mass) or different\nluminosities of the YSOs. More extensive overviews of the chemical\nevolution of star-forming regions are given by van Dishoeck \\& Blake\n(1998), Hartquist et al.\\ (1998), van Dishoeck \\& Hogerheijde (1999)\nand Langer et al.\\ (2000). Schilke et al.\\ (this volume) present high\nspatial resolution interferometer studies, whereas Macdonald \\&\nThompson (this volume) focus on submillimeter data of hot\ncore/ultracompact H~II regions. Ices are discussed by Ehrenfreund \\&\nSchutte (this volume).\n\n\\begin{figure}[t]\n\\plotfiddle{dishoeck_fig1.ps}{11.0cm}{0}{50}{50}{-150}{-30}\n\\caption{Overview of the SEST 230 GHz line survey of SgrB2 at the N, M and\nNW positions, illustrating the chemical differentiation in high-mass\nstar-forming regions (from:\nNummelin et al.\\ 1998).}\n\\label{fig-1}\n\\vspace{-0.3cm}\n\\end{figure}\n\n\n\\section{Submillimeter and Infrared Diagnostics}\n\nThe majority of molecules are detected at (sub-)millimeter\nwavelengths, and line surveys highlight the large variations in\nchemical composition between different YSOs, both within the same\nparent molecular cloud and between different clouds. The recent 1--3\nmm surveys of Sgr~B2 (Nummelin et al.\\ 1998, Ohishi \\& Kaifu 1999)\ndramatically illustrate the strong variations between various\npositions (see Figure~1). The North position is typical of\n`hot core'-type spectra, which are rich in lines of saturated\norganic molecules. This position has also been named \nthe `large molecule heimat'\n(e.g., Kuan \\& Snyder 1994, Liu \\& Snyder 1999). The Middle position\nhas strong SO and SO$_2$ lines, whereas the Northwest position has a\nless-crowded spectrum with lines of ions and long carbon chains. A\nsimilar differentiation has been observed for three positions in the\nW~3 giant molecular cloud by Helmich \\& van Dishoeck (1997), who\nsuggested an evolutionary sequence based on the chemistry.\n\n\\begin{figure}[t]\n\\plotfiddle{dishoeck_fig2.ps}{10cm}{0}{55}{55}{-150}{-115}\n\\caption{ISO-SWS spectra of two massive YSOs at different evolutionary stages.\nCep A ($L \\approx 2.4\\times 10^4$ L$_{\\odot}$) is in the embedded\nstage, whereas S~106 ($L \\approx 4.2\\times 10^4$ L$_{\\odot}$) is\nin a more evolved stage (from:\nvan den Ancker et al.\\ 2000a).}\n\\label{fig-2}\n\\end{figure}\n\n\nThe availability of complete infrared spectra from 2.4--200 $\\mu$m\nwith the {\\it Infrared Space Observatory }(ISO) allows complementary\nvariations in infrared features to be studied. Figure~2 shows an\nexample of ISO--SWS and LWS spectra of two objects: Cep A ($L \\approx\n2.4\\times 10^4$ L$_{\\odot}$) and S~106 ($L \\approx 4.2\\times 10^4$\nL$_{\\odot}$). The Cep A spectrum is characteristic of the deeply\nembedded phase, in which the silicates and ices in the cold envelope\nare seen in absorption. The S~106 spectrum is typical of a more\nevolved massive YSO, with strong atomic and ionic lines in emission\nand prominent PAH features. A similar sequence has been shown by\nEhrenfreund et al.\\ (1998) for a set of southern massive young stars\nwith luminosities up to $4\\times 10^5$ L$_{\\odot}$.\n\nThe most successful models for explaining these different chemical\ncharacteristics involve accretion of species in an icy mantle during the\n(pre-)collapse phase, followed by grain-surface chemistry and evaporation of\nices once the YSO has started to heat its surroundings (e.g., Millar 1997). \nThe evaporated molecules subsequently drive a rapid high-temperature gas-phase\nchemistry for a period of $\\sim 10^4 - 10^5$ yr, resulting in complex,\nsaturated organic molecules (e.g., Charnley et al.\\ 1992, 1995; Charnley 1997;\nCaselli et al.\\ 1993, Viti \\& Williams 1999). The abundance ratios of species\nsuch as CH$_3$OCH$_3$/CH$_3$OH and SO$_2$/H$_2$S show strong variations with\ntime, and may be used as `chemical clocks' for a period of 5000--30,000 yr\nsince evaporation. Once most of the envelope has cleared, the ultraviolet\nradiation can escape and forms a photon-dominated region (PDR) at the\nsurrounding cloud material, in which molecules are dissociated into radicals\n(e.g., HCN $\\to$ CN) and PAH molecules excited to produce infrared emission.\nThe (ultra-)compact H~II region gives rise to strong ionic lines due to\nphotoionization.\n\n\\begin{table}[t]\n\\caption{Chemical characteristics of massive star-forming regions}\n\\begin{center}\\scriptsize\n\\begin{tabular}{lllll}\n\\hline\n\\noalign{\\smallskip}\nComponent & Chemical & Submillimeter & Infrared & Examples \\\\\n & characteristics & diagnostics & diagnostics \\\\\n\\tableline\n\\noalign{\\smallskip}\nDense cloud & Low-T chemistry &Ions, long-chains &Simple ices & SgrB2 (NW) \\\\\n & & (HC$_5$N, ...) & (H$_2$O, CO$_2$) \\\\\n\\noalign{\\smallskip}\nCold envelope & Low-T chemistry, & Simple species & Ices & N7538 IRS9, \\\\\n & Heavy depletions & (CS, H$_2$CO) & (H$_2$O, CO$_2$, CH$_3$OH)\n & W~33A \\\\\n\\noalign{\\smallskip}\nInner warm & Evaporation & High T$_{\\rm ex}$ & High gas/solid, High\n & GL 2591, \\\\\nenvelope & & (CH$_3$OH) & T$_{\\rm ex}$, Heated ices \n & GL 2136 \\\\\n & & & (C$_2$H$_2$, H$_2$O, CO$_2$) \\\\\n\\noalign{\\smallskip}\nHot core & High-T chemistry & Complex organics & Hydrides & Orion hot core, \\\\\n & & (CH$_3$OCH$_3$, CH$_3$CN, & (OH, H$_2$O) \n& SgrB2(N),G34.3 \\\\\n&&vib.\\ excited mol.) && W~3(H$_2$O) \\\\\n\\noalign{\\smallskip}\nOutflow: & Shock chemistry, & Si- and S-species & \n Atomic lines, Hydrides & W~3 IRS5, \\\\\nDirect impact &Sputtering & (SiO, SO$_2$) &([S I], H$_2$O) & SgrB2(M) \\\\\n\\noalign{\\smallskip}\nPDR, Compact & Photodissociation,& Ions, radicals & Ionic lines, PAHs\n& S~140, \\\\\nH~II regions & Photoionization & (CN/HCN, CO$^+$) &([NeII], [CII])\n& W~3 IRS4 \\\\\n \n%\\noalign{\\vspace{-0.8cm}}\n\\tableline\n\\end{tabular}\n\\end{center}\n\\end{table}\n\n\nTable~1 summarizes the chemical characteristics of the\nvarious physical components, together with the observational\ndiagnostics at submillimeter and infrared wavelengths. \nWithin the single-dish submillimeter and ISO beams,\nmany of these components are blended together and interferometer\nobservations will be essential to disentangle them. Nevertheless, the\nsingle-dish data are useful because they encompass the entire envelope\nand highlight the dominant component in the beam. Combined\nwith the above chemical scenario, one may then attempt to establish an\nevolutionary sequence of the sources.\n\nThe physical distinction between the `hot core' and the warm\ninner envelope listed in Table~1 is currently not clear: does the `hot\ncore' represent a separate physical component or is it simply the\ninner warm envelope at a different stage of chemical evolution? Even\nfrom an observational point of view, there appear to be different\ntypes of `hot cores': some of them are internally heated by the young\nstar (e.g., W~3(H$_2$O)), whereas others may just be dense clumps of\ngas heated externally (e.g., the Orion compact ridge). This point\nwill be further discussed in \\S\\S 4 and 5. Disks are not included in\nTable~1, because little is known about their chemical characteristics,\nor even their existence, around high-mass YSOs (see Norris, this\nvolume).\n\n\n\\section{Intermediate-Mass YSOs}\n\nIntermediate-mass pre-main sequence stars, in particular the so-called\nHerbig Ae/Be stars, have received increased observational attention in\nrecent years (see Waters \\& Waelkens 1998 for a review). These stars\nhave spectral type A or B and show infrared excesses due to \ncircumstellar dust. Typical luminosities are in the range $10^2 -\n10^4$ L$_{\\odot}$, and several objects have been located within 1 kpc\ndistance. Systematic mapping of CO and the submillimeter continuum of\na sample of objects has been performed by Fuente et al.\\ (1998) and\nHenning et al.\\ (1998). The data show the dispersion of the envelope\nwith time starting from the deeply embedded phase (e.g.,\nLkH$\\alpha$234) to the intermediate stage of a PDR (e.g., HD 200775\nilluminating the reflection nebula NGC 7023) to the more evolved stage\nwhere the molecular gas has disappeared completely (e.g., HD 52721).\nThe increasing importance of photodissociation in the chemistry is\nprobed by the increase in the CN/HCN abundance ratio. This ratio has\nbeen shown in other high-mass sources to be an excellent tracer of\nPDRs (e.g., Simon et al. 1997, Jansen et al.\\ 1995). Line surveys of\nthese objects in selected frequency ranges would be useful to\ninvestigate their chemical complexity, especially in the embedded\nphase.\n\nISO-SWS observations of a large sample of Herbig Ae/Be stars have been\nperformed by van den Ancker et al.\\ (2000b,c). In the embedded phase,\nshock indicators such as [S I] 25.2 $\\mu$m are strong, whereas in the\nlater phases PDR indicators such as PAHs are prominent. An excellent\nexample of this evolutionary sequence is provided by three Herbig Ae\nstars in the BD+40$^o$4124 region ($d\\approx 1$ kpc). The data\nsuggest that in the early phases, the heating of the envelope is\ndominated by shocks, whereas in later phases it is controlled by\nultraviolet photons.\n\n\n\\begin{figure}[t]\n\\vspace{-3.8cm}\n\\plottwo{dishoeck_fig3a.ps}{dishoeck_fig3b.ps}\n\\vspace{-0.3cm}\n\\caption{Left: ISO-LWS spectra of the intermediate mass YSO \nLkH$\\alpha$234, showing strong atomic fine-structure lines of\n[C II] 158 $\\mu$m and [O~I] 63 $\\mu$m, but weak molecular CO and\nOH lines. Right: CO excitation diagram, indicating the presence\nof a warm ($T\\approx 200-900$~K), dense ($n>10^5$ cm$^{-3}$) \nregion (from:\nGiannini et al.\\ 2000).}\n\\label{fig-3}\n\\vspace{-0.5cm}\n\\end{figure}\n\n\nISO-LWS data have been obtained for a similar sample of Herbig Ae/Be\nstars by Lorenzetti et al.\\ (1999) and Giannini et al.\\ (2000), and\nare summarized by Saraceno et al.\\ (1999). The [C II] 158 $\\mu$m and\n[O I] 63 and 145 $\\mu$m lines are prominent in many objects and are\ndue primarily to the PDR component in the large LWS beam ($\\sim\n80''$). High-$J$ CO and OH far-infrared lines have been detected in\nsome objects and indicate the presence of a compact, high temperature\nand density region of $\\sim$1000 AU in size, presumably tracing the\ninner warm envelope (see Figure~3).\nFar-infrared lines of H$_2$O are seen in low-mass YSO spectra, but are\nweak or absent in those of intermediate- and high-mass YSOs, with the\nexception of Orion-KL and SgrB2 (e.g., Harwit et al.\\ 1998, Cernicharo\net al.\\ 1997, Wright et al.\\ 2000). The absence of H$_2$O lines in\nhigher-mass objects may be partly due to the larger distance of these\nobjects, resulting in substantial dilution in the LWS beam. However,\nphotodissociation of H$_2$O to OH and O by the enhanced ultraviolet radiation\nmay also play a role.\n\nIn summary, both the submillimeter and infrared diagnostics reveal an\nevolutionary sequence from the youngest `Group I' objects to `Group\nIII' objects (cf.\\ classification by Fuente et al.\\ 1998), in which\nthe envelope is gradually dispersed. Such a sequence is analogous to\nthe transition from embedded Class 0/I objects to more evolved Class\nII/III objects in the case of low-mass stars (Adams et al.\\ 1987). The\nISO data provide insight into the relative importance of the heating\nand removal mechanisms of the envelope. At the early stages of\nintermediate-mass star formation, shocks due to outflows appear to\ndominate whereas at later stages radiation is more important.\n\n\\section{Embedded, Infrared-Bright Massive YSOs}\n\n\\subsection{Sample}\n\nThe availability of complete, high quality ISO spectra for a\nsignificant sample of massive young stars provides a unique\nopportunity to study these sources through a combination of infrared\nand submillimeter spectroscopy, and further develop these diagnostics.\nVan der Tak et al.\\ (2000a) have selected a set of $\\sim$10 deeply\nembedded massive YSOs which are bright at mid-infrared wavelengths (12\n$\\mu$m flux $>$ 100 Jy), have luminosities of $10^3 - 2\\times 10^5$\nL$_{\\odot}$ and distances $d\\leq$4 kpc. The sources are all in an\nearly evolutionary state (comparable to the `Class 0/I' or `Group I'\nstages of low- and intermediate-mass stars), as indicated by their\nweak radio continuum emission and absence of ionic lines and PAH\nfeatures. In addition to ISO spectra, JCMT submillimeter data and\nOVRO interferometer observations have been obtained. For most of the\nobjects high spectral resolution ground-based infrared data of CO,\n$^{13}$CO and H$_3^+$ are available (Mitchell et al.\\ 1990, Geballe \\&\nOka 1996, McCall et al.\\ 1999), and occasionally H$_2$ (Lacy et\nal.\\ 1994, Kulesa et al.\\ 1999). For comparison, 5 infrared-weak\nsources with similar luminosities are studied at submillimeter\nwavelengths only. This latter set includes hot cores and ultracompact\nH~II regions such as W~3(H$_2$O), IRAS 20126+4104 (Cesaroni et al.\\ \n1997, 1999), and NGC~6334 IRS1.\n\n\\subsection{Physical structure of the envelope}\n\nIn order to derive molecular abundances from the observations, a good\nphysical model of the envelope is a prerequisite. Van der Tak et al.\\ \n(1999, 2000a) outline the techniques used to constrain the temperature\nand density structure (Figure~4). The total mass within the\nbeam is derived from submillimeter photometry, whereas the size scale\nof the envelope is constrained from line and continuum maps. The dust\nopacity has been taken from Ossenkopf \\& Henning (1994) and yields\nvalues for the mass which are consistent with those derived from\nC$^{17}$O for warm sources where CO is not depleted\nonto grains.\n\n\n\\begin{figure}[t]\n\\plotfiddle{dishoeck_fig4.ps}{7.7cm}{0}{45}{45}{-120}{-60}\n\\caption{Overview of method used for constraining the temperature and density\nstructure of envelopes. A power-law density structure with trial values\nfor the exponent\n$\\alpha_i$ and molecular abundances $X_j$ is adopted\n(based on: van der Tak et al.~2000a).}\n\\label{fig-4}\n\\end{figure}\n\n\nThe temperature structure of the dust is calculated taking the\nobserved luminosity of the source, given a power-law density structure\n(see below). At large distances from the star, the temperature follows\nthe optically thin relation $\\propto r^{-0.4}$, whereas at smaller\ndistances the dust becomes optically thick at infrared wavelengths and\nthe temperature increases more steeply (see Figure~5). It is assumed\nthat $T_{\\rm gas}=T_{\\rm dust}$, consistent with explicit calculations\nof the gas and dust temperatures by, e.g., Doty \\& Neufeld (1997)\nfor these high densities.\n\nThe continuum data are sensitive to temperature and column density,\nbut not to density. Observations of a molecule with a large dipole\nmoment are needed to subsequently constrain the density structure. One\nof the best choices is CS and its isotope C$^{34}$S, for which lines\nranging from $J$=2--1 to 10--9 have been observed. Assuming a\npower-law density profile $n(r)= n_o (r/r_o)^{-\\alpha}$, values of\n$\\alpha$ can be determined from minimizing $\\chi^2$ between the CS\nline data and excitation models. The radiative transfer in the lines\nis treated through a Monte-Carlo method. The best fit to the data on\nthe infrared-bright sources is obtained for $\\alpha = 1.0 - 1.5$,\nwhereas the hot core/compact H~II region sample requires higher\nvalues, $\\alpha \\approx 2$. This derivation assumes that the CS\nabundance is constant through the envelope; if it increases with\nhigher temperatures, such as may be the case for hot cores, the values\nof $\\alpha$ are lowered. Note that the derived values of\n$\\alpha=1.0-1.5$ are lower than those found for deeply embedded\nlow-mass objects, where $\\alpha\\approx 2$ (e.g., Motte et al.\\ 1998,\nHogerheijde et al.\\ 1999).\n\n\\begin{figure}[t]\n\\plotfiddle{dishoeck_fig5.ps}{7.0cm}{-90}{45}{45}{-170}{260}\n\\vspace{-0.3cm}\n\\caption{Derived temperature and density structure for the envelope\naround the massive YSO\nGL 2591 (L=$2\\times 10^4$ L$_{\\odot}$, $d$=1 kpc). \nThe critical densities of the CS 2--1 and 10--9 lines are\nindicated, as are the typical beam sizes of the JCMT \nat 345 GHz and OVRO at 100 GHz (based on: van der Tak et \nal.\\ 1999).}\n\\label{fig-5}\n\\vspace{-0.5cm}\n\\end{figure}\n\n\nFigure 5 displays the derived temperature and density structure\nfor the source GL 2591, together with the sizes of the JCMT and\nOVRO beams. While the submillimeter data are weighted toward the\ncolder, outer envelope, the infrared absorption line observations sample\na pencil-beam line of sight toward the YSO and are more sensitive to\nthe inner warm ($\\sim 1000$~K) region. On these small scales, the\nenvelope structure deviates from a radial power law, which decreases\nthe optical depth at near-infrared wavelengths by a factor of \n$\\sim 3$ (van der Tak et al.\\\n1999).\n\n\nFor sources for which interferometer data are available, unresolved\ncompact continuum emission is detected on scales of a few thousand AU\nor less. This emission is clearly enhanced compared with that\nexpected from the inner ``tip'' of the power-law envelope, and its\nspectral index indicates optically thick warm dust, most likely in a\ndense circumstellar shell or disk. The presence of this shell or disk\nis also indicated by the prevalence of blue-shifted outflowing dense\ngas without a red-shifted counterpart on $< 10''$ scales.\n\n\n\\subsection{Chemical structure: infrared absorption lines}\n\nThe ISO-SWS spectra of the infrared-bright sources show absorption by\nvarious gas-phase molecules, in addition to strong features by ices.\nMolecules such as CO$_2$ (van Dishoeck et al.\\ 1996,\nBoonman et al.\\ 1999, 2000a), H$_2$O (van Dishoeck \\& Helmich 1996, Boonman\net al.\\ 2000b), CH$_4$ (Boogert et al.\\ 1998), HCN and C$_2$H$_2$\n(Lahuis \\& van Dishoeck 2000) have been detected (see also van\nDishoeck 1998, Dartois et al.\\ 1998).\n\nIn the infrared, absorption out of all $J$-levels is observed in a\nsingle spectrum. The excitation temperatures $T_{\\rm ex}$ of the\nvarious molecules, calculated assuming LTE, range from $\\ltsim 100$ to\n$\\sim 1000$~K between sources, giving direct information on \nthe physical component in which the molecules reside. While CO \nis well-mixed throughout the envelopes, H$_2$O, HCN and C$_2$H$_2$ are\nenhanced at high temperatures. In contrast, CO$_2$ seems to avoid the\nhottest gas. High spectral resolution ground-based data of HCN and\nC$_2$H$_2$ by Carr et al.\\ (1995) and Lacy et al.\\ (1989) for a few\nobjects suggest line widths of at most a few km s$^{-1}$, excluding an\norigin in outflowing gas.\n\nThe abundances of H$_2$O, HCN and C$_2$H$_2$ increase by factors of\n$\\gtsim 10$ with increasing $T_{\\rm ex}$ (see Figure~7). The warm\nH$_2$O must be limited to a $\\ltsim 1000$~AU region, since the pure\nrotational lines are generally not detected in the $80''$ ISO-LWS beam\n(Wright et al.\\ 1997). For CO$_2$, the abundance variation between\nsources is less than a factor of 10, and no clear trend with $T_{\\rm\n ex}$ is found. For the same sources, the H$_2$O and CO$_2$ ice\nabundances show a decrease by an order of magnitude, consistent with\nevaporation of the ices. However, the gas-phase H$_2$O and CO$_2$\nabundances are factors of $\\sim 10$ lower than expected if all\nevaporated molecules stayed in the gas phase, indicating that\nsignificant chemical processing occurs after evaporation. More\ndetailed modeling using the source structures derived from\nsubmillimeter data is in progress.\n\n\\begin{figure}[t]\n\\plotfiddle{dishoeck_fig6.ps}{6.8cm}{-90}{50}{50}{-210}{260}\n\\caption{{\\it Left:}~Abundance of HCN,\n$N$(HCN)/$N_{\\rm tot}$(H$_2$), as a function of the\n$^{13}$CO excitation temperature measured by\nMitchell et al.\\ (1990). {\\it Middle:} Abundance of H$_2$O in the warm gas\n$N$(H$_2$O)/$N_{\\rm warm}$(H$_2$) as a function of $^{13}$CO excitation\ntemperature;\n{\\it Right:}~Abundance of H$_2$O ice as a function of\n$^{13}$CO excitation temperature. The same trend\nis found if the dust temperature, as derived from the 45/100 $\\mu$m\nflux, is used (based on: Lahuis \\& van Dishoeck 2000; van Dishoeck 1998).}\n\\label{fig-6}\n\\end{figure}\n\n\n\\subsection{Chemical structure: submillimeter emission}\n\nThe JCMT data of the infrared-bright objects show strong lines, but\nlack the typical crowded `hot core' spectra observed for objects such\nas W~3(H$_2$O) and NGC 6334 IRS1. Complex organics such as\nCH$_3$OCH$_3$ and CH$_3$OCHO are detected in some sources (e.g., GL\n2591, NGC 7538 IRS1), but are not as prominent as in the comparison\nsources. Yet warm gas is clearly present in these objects.\nIs the `hot core' still too small to be picked up by the\nsingle dish beams, or are the abundances of these molecules not (yet)\nenhanced?\n\nTo investigate this question, \nvan der Tak et al.\\ (2000b) consider the analysis of\ntwo species, H$_2$CO and CH$_3$OH. Both\nspecies have many lines throughout the submillimeter originating from\nlow- and high-lying energy levels. Given the physical structure\ndetermined in \\S 4.2, abundance {\\it profiles} can be constrained. Two\nextreme, but chemically plausible models are considered: (i) a model\nwith a constant abundance throughout the envelope. This model is\nmotivated by the fact that pure gas-phase reaction schemes do not show\nlarge variations in calculated abundances between 20 and 100~K; (ii) a\nmodel in which the abundance `jumps' to a higher value at the ice\nevaporation temperature, $T_d\\approx 90$~K. In this model, the\nabundances in the outer envelope are set at those observed in cold\nclouds, so that the only free parameter is the amount of abundance\nincrease.\n\nIt is found that the H$_2$CO data can be well fit with a constant\nabundance of a few $\\times 10^{-9}$ throughout the envelope. However,\nthe high $J,K$ data for CH$_3$OH require a jump in its abundance from\n$\\sim 10^{-9}$ to $\\sim 10^{-7}$ for the warmer sources. This is\nconsistent with the derived excitation temperatures: H$_2$CO has a\nrather narrow range of $T_{\\rm ex}$=50--90~K, whereas CH$_3$OH shows\n$T_{\\rm ex}$=30--200~K. Moreover, the interferometer maps of CH$_3$OH\nrule out constant abundance models. The jump observed for CH$_3$OH is\nchemically plausible since this molecule is known to be present in icy\ngrain mantles with abundances of 5--40\\% with respect to H$_2$O ice,\ni.e., $\\sim 10^{-7}-10^{-6}$ w.r.t.\\ H$_2$. Similar increases in the\nabundances of organic molecules (e.g., CH$_3$OH, C$_2$H$_3$CN, ....)\nare found with increasing $T_{\\rm dust}$ for a set of `hot--core'\nobjects by Ikeda \\& Ohishi (1999).\n\n\n\\subsection{Comparison with chemical models}\n\nBoth the infrared and submillimeter data show increases in the\nabundances of various molecules with increasing temperature. Four\ntypes of species can be distinguished: (i) `passive' molecules which\nare formed in the gas phase, freeze out onto grains during the cold\n(pre-)collapse phase and are released during warm-up without chemical\nmodification (e.g., CO, C$_2$H$_2$); (ii) molecules which are formed\non the grains during the cold phase by surface reactions and are\nsubsequently released into the warm gas (e.g., CH$_3$OH); (iii)\nmolecules which are formed in the warm gas by gas-phase reactions with\nevaporated molecules (e.g., CH$_3$OCH$_3$); (iv) molecules which are\nformed in the hot gas by high temperature reactions (e.g., HCN). These\ntypes of molecules\nare associated with characteristic temperatures of (a) $T_{\\rm\n dust}<20$~K, where CO is frozen out; the presence of CO ice is\nthought to be essential for the formation of CH$_3$OH; (b) $T_{\\rm\n dust} \\approx 90$~K, where all ices evaporate on a time scale of\n$<10^5$ yr; and (c) $T_{\\rm gas}>230$~K, where gas-phase reactions\ndrive the available atomic oxygen into water through the reactions O +\nH$_2$ $\\to$ OH $\\to$ H$_2$O (Ceccarelli et al.\\ 1996, Charnley 1997).\nAtomic oxygen is one of the main destroyers of radicals and carbon\nchains, so that its absence leads to enhanced abundances of species\nlike HCN and HC$_3$N in hot gas.\n\nWater is abundantly formed on the grains, but the fact that the\nH$_2$O abundance in the hot gas is not as large as that of the ices\nsuggests that H$_2$O is broken down to O and OH after evaporation by\nreactions with H$_3^+$. H$_2$O can subsequently be reformed in warm\ngas at temperatures above $\\sim$230~K, but Figure~7 indicates that not\nall available gas-phase oxygen is driven into H$_2$O, as the models\nsuggest. The low abundance of CO$_2$ in the warm gas is still a\npuzzle, since evaporation of abundant CO$_2$ ice is observed. The\nmolecule must be broken down rapidly in the warm gas, with no\nreformation through the CO + OH $\\to$ CO$_2$ reaction (see question by\nMinh).\n\n\\subsection{Evolution?}\n\nThe objects studied by van der Tak et al.\\ (2000a) are all in an early\nstage of evolution, when the young stars are still deeply embedded in\ntheir collapsing envelope. Nevertheless, even within this narrow\nevolutionary range, there is ample evidence for physical and chemical\ndifferentiation of the sources. This is clearly traced by the\nincrease in the gas/solid ratios, the increase in abundances of several\nmolecules, the decrease in the ice abundances, and the increase\nof the amount of crystalline ice with increasing temperature\n(Boogert et al.\\ 2000a).\n\nThe fact that the various indicators involve different\ncharacteristic temperatures ranging from $<$50 K (evaporation of\napolar ices) to 1000 K ($T_{\\rm ex}$ of gas-phase molecules)\nindicates that the heating is not a local effect, but that `global\nwarming' occurs throughout the envelope. Moreover, it cannot be a\ngeometrical line-of-sight effect in the mid-infrared data, since the\nfar--infrared continuum (45/100 $\\mu$m) and submillimeter line data\n(CH$_3$OH) show the same trend. Shocks with different filling factors\nare excluded for the same reason.\n\nCan we relate this `global warming' of the envelope to an evolutionary\neffect, or is it determined by other factors? The absence of a\ncorrelation of the above indicators with luminosity or mass of the\nsource argues against them being the sole controlling factor. The\nonly significant trend is found with the ratio of envelope mass over\nstellar mass. The physical interpretation of such a relation would be\nthat with time, the envelope is dispersed by the star, resulting in a\nhigher temperature throughout the envelope.\n\n\\section{Outstanding questions and future directions}\n\nThe results discussed here suggest that the observed chemical abundance and\ntemperature variations can indeed be used to trace the evolution of\nthe sources, and that, as in the case of low- and intermediate-mass\nstars, the dispersion of the envelope plays a crucial role. \nThe combination of infrared and submillimeter diagnostics\nis very important in the analysis. An\nimportant next step would be to use these diagnostics to probe a much\nwider range of evolutionary stages for high-mass stars, especially in\nthe hot core and (ultra-)compact H II region stages, to develop a more\ncomplete scenario of high-mass star formation. The relation between\nthe inner warm envelope and the `hot core' is still uncertain: several\nobjects have been observed which clearly have hot gas and evaporated\nices (including CH$_3$OH) in their inner regions, but which do not\nshow the typical crowded `hot core' submillimeter spectra. Are these\nobjects just on their way to the `hot core' chemical phase? Or is the\n`hot core' a separate physical component, e.g., a dense shell at the\nedge of the expanding hyper-compact H~II region due to the pressure\nfrom the ionized gas, which is still too small to be\npicked up by the single-dish beams? In either case, time or evolution\nplays a role and would constrain the ages of the infrared-bright\nsources to less than a few $\\times 10^4$ yr since evaporation.\nInterferometer data provide evidence for the presence of a separate\nphysical component in the inner 1000 AU, but lack the spatial\nresolution to distinguish a shell from any remnant disk, for example\non kinematic grounds. \n\nAn important difference between high- and low-mass objects may be the\nmechanism for the heating and dispersion of their envelopes. For\nlow-mass YSOs, entrainment of material in outflows is the\ndominant process (Lada 1999). For intermediate-mass stars, outflows\nare important in the early phase, but ultraviolet radiation\nbecomes dominant in the later stages (see \\S~3). The situation for\nhigh-mass stars is still unclear. The systematic increase in\ngas/solid ratios and gas-phase abundances point to global heating of\nthe gas and dust, consistent with a radiative mechanism. However, a\nclear chemical signature of ultraviolet radiation on gas-phase species\nand ices in the embedded phase has not yet been identified, making it\ndifficult to calibrate its effect. On the other hand, high-mass stars\nare known to have powerful outflows and winds, but a quantitative\ncomparison between their effectiveness in heating an extended part\nof the envelope and removing material is still\nlacking. Geometrical effects are more important in less embedded\nsystems, as is the case for low-mass stars, where the circumstellar\ndisk may shield part of the envelope from heating (Boogert et al.\\ \n2000b).\n\n\nTo what extent does the chemical evolution picture also apply to\nlow-mass stars? Many of the chemical processes and characteristics\nlisted in Table~1 are also known to occur for low-mass YSOs, but\nseveral important diagnostic tools are still lacking. In particular,\nsensitive mid-infrared spectroscopy is urgently needed to trace the evolution\nof the ices for low-mass YSOs and determine gas/solid ratios. Also,\nmolecules as complex as CH$_3$OCH$_3$ and C$_2$H$_5$CN have not yet\nbeen detected toward low-mass YSOs, although the limits are not very\nstringent (e.g., van Dishoeck et al.\\ 1995). Evaporation of ices\nclearly occurs in low-mass environments as evidenced by enhanced\nabundances of grain-surface molecules in shocks (e.g., Bachiller \\&\nP\\'erez-Guti\\'errez 1997), but whether a similar `hot core' chemistry\nensues is not yet known. Differences in the \nH/H$_2$ ratio and temperature structure in the (pre-)collapse\nphase may affect the\ngrain-surface chemistry and the ice composition,\nleading to different abundances of solid CH$_3$OH, which \nis an essential ingredient\nfor building complex molecules.\n\nFuture instrumentation with high spatial resolution ($< 1''$) and\nhigh sensitivity will be essential to make progress in our\nunderstanding of the earliest phase of massive star formation, in\nparticular the SMA and ALMA at submillimeter wavelengths, and SIRTF,\nSOFIA, FIRST and ultimately NGST at mid- and far-infrared wavelengths.\n\n\n\n\\acknowledgments\n\nThe authors are grateful to G.A. Blake, A.C.A.\\ Boogert, A.M.S.\\ Boonman, P.\\ \nEhrenfreund, N.J.\\ Evans, T.\\ Giannini, F.\\ Lahuis, L.G.\\ Mundy, A.\\ \nNummelin, W.A.\\ Schutte, A.G.G.M.\\ Tielens, and M.E.\\ van den Ancker\nfor discussions, collaborations and figures. 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D. 1995, \n\\apj, 447, 760 \n\n\\reference\nvan Dishoeck, E.F. \\& Helmich, F.P. 1996, A\\&A, 315, L177\n\n\\reference\nvan Dishoeck, E.F., Helmich, F.P., de Graauw, Th. et al. 1996,\nA\\&A, 315, L349\n\n\\reference\nvan Dishoeck, E.F. \\& Hogerheijde, M.R. 1999, in Origin of Stars and Planetary\nSystems,\neds.\\ C.J.\\ Lada and N.\\ Kylafis (Dordrecht:\nKluwer), p.\\ 97\n\n\\reference\nvan Dishoeck, E.F. et al.\\ 1999, in The Universe as seen by ISO,\neds.\\ P.\\ Cox and M.F.\\ Kessler (Noordwijk: ESTEC), ESA SP-427, p.\\ 437\n\n\n\\reference\nWaters, L.B.F.M.\\ \\& Waelkens, C.\\ 1998, ARAA, 36, 233\n\n\n\\reference\nWright, C.M., van Dishoeck, E.F., Helmich, F.P., Lahuis, F., Boogert, A.C.A.,\n\\& de Graauw, Th. 1997, \nin First ISO Workshop on Analytical Spectroscopy,\nESA SP-419, p. 37\n\n\\reference\nWright, C.M., van Dishoeck, E.F., Black, J.H., Feuchtgruber, H.,\nCernicharo, J., Gonz\\'alez-Alfonso, E., \\& de Graauw,\nTh.\\ 2000, A\\&A, in press \n\n\\end{references}\n\n\n\\begin{question}{M.\\ Ohishi}\nI agree with the point you mentioned, that the chemical differences among\nhot cores is due to a difference of evolutionary stage. Now we have\nseveral well-known hot cores such as Orion KL/S, W~3 IRS5/H$_2$O/IRS4,\nSgrB2 N/M/NW etc. Can you give us your personal view on the evolutionary\ndifferences of these sources?\n\\end{question} \n\n\\begin{answer}{E.F.\\ van Dishoeck}\nVan der Tak et al.\\ (2000a) argue that the infrared-bright objects such as W~3\nIRS5 represent an earlier evolutionary phase than the hot cores, on the basis\nof an anti-correlation with the radio continuum. The physical picture is that\nthe ionizing UV radiation and stellar winds push the hottest dust in the inner\nregions further out, decreasing the temperature of the dust and thus the\nnear-infrared continuum. At the same time, the size of the region which can be\nionized is increased. The `erosion' of the envelopes thus occurs from the\ninside out. For other sources, infrared diagnostics are lacking, so that the\nsituation is less clear. It would be great if chemistry could help to tie down\nthe time scales of the various phases.\n\\end{answer}\n\n\\begin{question}{W.\\ Irvine}\nHow do you interpret the behavior of the PAH features as a function of\nevolutionary stage in the sources that you discussed?\n\\end{question}\n\n\\begin{answer}{E.F.\\ van Dishoeck}\nThe absence of PAH features in the early embedded stage can be due either\nto a lack of ultraviolet radiation to excite the features or to an absence\nof the carriers. Manske \\& Henning (1999, A\\&A 349, 907) have argued \nfor the case of Herbig Ae/Be stars that\nthere should be sufficient radiation to excite PAHs in the envelope/disk\nsystem,\nso that the lack is likely due to the absence of the PAHs\nthemselves. Perhaps the PAHs have accreted into the icy mantles at the\nhigh densities in the inner envelope and do not evaporate\nand/or are chemically transformed into\nother more refractory species on grains. Alternatively, the region producing\nultraviolet radiation (H~II region) may be very small \nin these massive objects, and the photons may not reach the PAH-rich\nmaterial or have a very small beam filling factor.\nOnce the envelope breaks up and\nultraviolet radiation can escape to the less dense\nouter envelope, the PAH features from those\nregions will appear in spectra taken with large beams.\n\\end{answer}\n\n\\begin{question}{T.\\ Geballe}\nYou said that there is little evidence of the effect of ultraviolet radiation\non solid-state chemistry. Isn't the 4.6 $\\mu$m XCN feature a good example\nof that influence?\n\\end{question}\n\n\\begin{answer}{E.F.\\ van Dishoeck}\nThe `XCN' feature is indeed the best candidate for tracing the \nultraviolet processing\nof ices. If ascribed to OCN$^-$, it likely involves HNCO as\na precursor. In the laboratory, HNCO is produced by photochemical\nreactions of CO and NH$_3$, but in the interstellar medium grain surface\nchemistry is an alternative possibility which does not necessarily\ninvolve ultraviolet radiation (see Ehrenfreund \\& Schutte,\nthis volume). \n\\end{answer}\n\n\\begin{question}{Y.C.\\ Minh}\nDo you have an explanation of the low and constant abundances of CO$_2$\nin the gas phase?\n\\end{question}\n\n\\begin{answer}{E.F.\\ van Dishoeck}\nCharnley \\& Kaufman (2000, ApJ, 529, L111) argue that the evaporated CO$_2$ is\ndestroyed by reactions with atomic hydrogen at high temperatures in shocks.\nThis is an interesting suggestion, but needs to be tested against other\nspecies such as H$_2$O and H$_2$S which can be destroyed by\nreactions with atomic hydrogen as well. Also, the amount of material \nin the envelope that can be affected by shocks is not clear.\n\\end{answer}\n\n\\end{document}\n\n\n\n"}],"string":"[\n {\n \"name\": \"dishoeck.tex\",\n \"string\": \"% SAMPLE1.TEX -- WGAS sample paper with minimal markup.\\n\\n% Lines starting with \\\"%\\\" are comments; they will be ignored by LaTeX.\\n\\n\\\\documentstyle[11pt,newpasp,psfig,epsf,twoside]{article}\\n\\\\def\\\\gtsim{{_>\\\\atop{^\\\\sim}}}\\n\\\\def\\\\ltsim{{_<\\\\atop{^\\\\sim}}}\\n\\n\\\\begin{document}\\n\\n\\\\title{Chemistry in the Envelopes around Massive Young Stars}\\n\\\\author{Ewine F.\\\\ van Dishoeck and Floris F.S.\\\\ van der Tak}\\n\\\\affil{Leiden Observatory, P.O.\\\\ Box 9513, 2300 RA Leiden,\\nThe Netherlands}\\n\\n\\\\begin{abstract}\\nRecent observational studies of intermediate- and high-mass\\n star-forming regions at submillimeter and infrared wavelengths are\\n reviewed, and chemical diagnostics of the different physical\\n components associated with young stellar objects are summarized.\\n Procedures for determining the temperature, density and abundance\\n profiles in the envelopes are outlined. A detailed study of a set of\\n infrared-bright massive young stars reveals systematic increases in\\n the gas/solid ratios, the abundances of evaporated molecules, and the\\n fraction of heated ices with increasing temperature. Since these\\n diverse phenomena involve a range of temperatures from $<100\\\\,$K to\\n 1000~K, the enhanced temperatures must be communicated to both the\\n inner and outer parts of the envelopes. This `global heating'\\n plausibly results from the gradual dispersion of the envelopes with\\n time. Similarities and differences with low-mass YSOs are discussed.\\n The availability of accurate physical models will allow chemical\\n models of ice evaporation followed by `hot core' chemistry to be\\n tested in detail.\\n\\n\\n\\\\end{abstract}\\n\\n\\n%% Keywords: High-mass star formation, ices, hot cores, envelopes\\n%% \\n%% Objects: Orion-KL, Orion-IRc2, SGrB2, W~3 IRS5, W~3(H$_2$O), AFGL 2591,\\n%% AFGL 2136, NGC 7538 IRS9, W~33A, G34.3, S 140, W~3 IRS4\\n%% Molecules: CO, C$^{17}$O, CS, H$_2$CO, HC$_5$N, H$_2$O, CO$_2$,\\n%% CH$_3$OH, CH$_3$OCH$_3$, CH$_3$CN, C$_2$H$_2$, S~I, PAHs\\n%% OH, SiO, SO$_2$, CN, HCN, C~II, CO$^+$\\n\\n\\\\section{Introduction}\\n\\nMassive star-forming regions have traditionally been prime targets for\\nastrochemistry owing to their bright molecular lines (e.g., Johansson\\net al.\\\\ 1984, Cummins et al.\\\\ 1986, Irvine et al.\\\\ 1987, Ohishi 1997).\\nMassive young stellar objects (YSOs) have luminosities of $\\\\sim 10^4 -\\n10^6$ L$_\\\\odot$ and involve young O- and B-type stars. Because their\\nformation proceeds more rapidly than that of low-mass stars and\\ninvolves ionizing radiation, substantial chemical differences may be\\nexpected. The formation of high mass stars is much less well\\nunderstood than that of low-mass stars. For\\nexample, observational phenomena such as ultracompact H II regions,\\nhot cores, masers and outflows have not yet been linked into a single\\nevolutionary picture. Chemistry may well be an important diagnostic\\ntool in establishing such a sequence.\\n \\nMost of the early work on massive star-forming regions has centered on\\ntwo sources, Orion--KL and SgrB2. Numerous line surveys at millimeter\\n(e.g., Blake et al.\\\\ 1987, Turner 1991) and submillimeter (Jewell et\\nal.\\\\ 1989, Sutton et al.\\\\ 1991, 1995, Schilke et al.\\\\ 1997)\\nwavelengths have led to an extensive inventory of molecules through\\nidentification of thousands of lines. In addition, the surveys have\\nshown strong chemical variations between different sources.\\n\\nIn recent years, new observational tools have allowed a more detailed and\\nsystematic study of the envelopes of massive YSOs. Submillimeter observations\\nroutinely sample smaller beams (typically 15$''$ vs.\\\\ 30$''$--1$'$ ) and\\nhigher critical densities ($\\\\geq 10^6$ vs.\\\\ $10^4$ cm$^{-3}$) than the earlier\\nwork. Moreover, interferometers at 3 and 1 millimeter provide maps with\\nresolutions of $0.5''$--5$''$. Finally, ground- and space-based infrared\\nobservations allow both the gas and the ices to be sampled (e.g., Evans et\\nal.\\\\ 1991, van Dishoeck et al.\\\\ 1999). These observational developments have\\nled to a revival of the study of massive star formation within the last few\\nyears. Recent overviews of the physical aspects of high-mass star formation\\nare found in Churchwell (1999) and Garay \\\\& Lizano (1999).\\n\\n\\nIn this brief review, we will first summarize available observational\\ndiagnostics to study the different phases and physical components\\nassociated with massive star formation. Subsequently, an overview of\\nrecent results on intermediate mass YSOs is given, which are often\\nbetter characterized than their high-mass counterparts because of\\ntheir closer distance. Subsequently, we will discuss a specific sample\\nof embedded massive YSOs which have been studied through a combination\\nof infrared and submillimeter data. After illustrating\\nthe modeling techniques, we address the question how the\\nobserved chemical variations are related to evolutionary effects,\\ndifferent conditions in the envelope (e.g., $T$, mass) or different\\nluminosities of the YSOs. More extensive overviews of the chemical\\nevolution of star-forming regions are given by van Dishoeck \\\\& Blake\\n(1998), Hartquist et al.\\\\ (1998), van Dishoeck \\\\& Hogerheijde (1999)\\nand Langer et al.\\\\ (2000). Schilke et al.\\\\ (this volume) present high\\nspatial resolution interferometer studies, whereas Macdonald \\\\&\\nThompson (this volume) focus on submillimeter data of hot\\ncore/ultracompact H~II regions. Ices are discussed by Ehrenfreund \\\\&\\nSchutte (this volume).\\n\\n\\\\begin{figure}[t]\\n\\\\plotfiddle{dishoeck_fig1.ps}{11.0cm}{0}{50}{50}{-150}{-30}\\n\\\\caption{Overview of the SEST 230 GHz line survey of SgrB2 at the N, M and\\nNW positions, illustrating the chemical differentiation in high-mass\\nstar-forming regions (from:\\nNummelin et al.\\\\ 1998).}\\n\\\\label{fig-1}\\n\\\\vspace{-0.3cm}\\n\\\\end{figure}\\n\\n\\n\\\\section{Submillimeter and Infrared Diagnostics}\\n\\nThe majority of molecules are detected at (sub-)millimeter\\nwavelengths, and line surveys highlight the large variations in\\nchemical composition between different YSOs, both within the same\\nparent molecular cloud and between different clouds. The recent 1--3\\nmm surveys of Sgr~B2 (Nummelin et al.\\\\ 1998, Ohishi \\\\& Kaifu 1999)\\ndramatically illustrate the strong variations between various\\npositions (see Figure~1). The North position is typical of\\n`hot core'-type spectra, which are rich in lines of saturated\\norganic molecules. This position has also been named \\nthe `large molecule heimat'\\n(e.g., Kuan \\\\& Snyder 1994, Liu \\\\& Snyder 1999). The Middle position\\nhas strong SO and SO$_2$ lines, whereas the Northwest position has a\\nless-crowded spectrum with lines of ions and long carbon chains. A\\nsimilar differentiation has been observed for three positions in the\\nW~3 giant molecular cloud by Helmich \\\\& van Dishoeck (1997), who\\nsuggested an evolutionary sequence based on the chemistry.\\n\\n\\\\begin{figure}[t]\\n\\\\plotfiddle{dishoeck_fig2.ps}{10cm}{0}{55}{55}{-150}{-115}\\n\\\\caption{ISO-SWS spectra of two massive YSOs at different evolutionary stages.\\nCep A ($L \\\\approx 2.4\\\\times 10^4$ L$_{\\\\odot}$) is in the embedded\\nstage, whereas S~106 ($L \\\\approx 4.2\\\\times 10^4$ L$_{\\\\odot}$) is\\nin a more evolved stage (from:\\nvan den Ancker et al.\\\\ 2000a).}\\n\\\\label{fig-2}\\n\\\\end{figure}\\n\\n\\nThe availability of complete infrared spectra from 2.4--200 $\\\\mu$m\\nwith the {\\\\it Infrared Space Observatory }(ISO) allows complementary\\nvariations in infrared features to be studied. Figure~2 shows an\\nexample of ISO--SWS and LWS spectra of two objects: Cep A ($L \\\\approx\\n2.4\\\\times 10^4$ L$_{\\\\odot}$) and S~106 ($L \\\\approx 4.2\\\\times 10^4$\\nL$_{\\\\odot}$). The Cep A spectrum is characteristic of the deeply\\nembedded phase, in which the silicates and ices in the cold envelope\\nare seen in absorption. The S~106 spectrum is typical of a more\\nevolved massive YSO, with strong atomic and ionic lines in emission\\nand prominent PAH features. A similar sequence has been shown by\\nEhrenfreund et al.\\\\ (1998) for a set of southern massive young stars\\nwith luminosities up to $4\\\\times 10^5$ L$_{\\\\odot}$.\\n\\nThe most successful models for explaining these different chemical\\ncharacteristics involve accretion of species in an icy mantle during the\\n(pre-)collapse phase, followed by grain-surface chemistry and evaporation of\\nices once the YSO has started to heat its surroundings (e.g., Millar 1997). \\nThe evaporated molecules subsequently drive a rapid high-temperature gas-phase\\nchemistry for a period of $\\\\sim 10^4 - 10^5$ yr, resulting in complex,\\nsaturated organic molecules (e.g., Charnley et al.\\\\ 1992, 1995; Charnley 1997;\\nCaselli et al.\\\\ 1993, Viti \\\\& Williams 1999). The abundance ratios of species\\nsuch as CH$_3$OCH$_3$/CH$_3$OH and SO$_2$/H$_2$S show strong variations with\\ntime, and may be used as `chemical clocks' for a period of 5000--30,000 yr\\nsince evaporation. Once most of the envelope has cleared, the ultraviolet\\nradiation can escape and forms a photon-dominated region (PDR) at the\\nsurrounding cloud material, in which molecules are dissociated into radicals\\n(e.g., HCN $\\\\to$ CN) and PAH molecules excited to produce infrared emission.\\nThe (ultra-)compact H~II region gives rise to strong ionic lines due to\\nphotoionization.\\n\\n\\\\begin{table}[t]\\n\\\\caption{Chemical characteristics of massive star-forming regions}\\n\\\\begin{center}\\\\scriptsize\\n\\\\begin{tabular}{lllll}\\n\\\\hline\\n\\\\noalign{\\\\smallskip}\\nComponent & Chemical & Submillimeter & Infrared & Examples \\\\\\\\\\n & characteristics & diagnostics & diagnostics \\\\\\\\\\n\\\\tableline\\n\\\\noalign{\\\\smallskip}\\nDense cloud & Low-T chemistry &Ions, long-chains &Simple ices & SgrB2 (NW) \\\\\\\\\\n & & (HC$_5$N, ...) & (H$_2$O, CO$_2$) \\\\\\\\\\n\\\\noalign{\\\\smallskip}\\nCold envelope & Low-T chemistry, & Simple species & Ices & N7538 IRS9, \\\\\\\\\\n & Heavy depletions & (CS, H$_2$CO) & (H$_2$O, CO$_2$, CH$_3$OH)\\n & W~33A \\\\\\\\\\n\\\\noalign{\\\\smallskip}\\nInner warm & Evaporation & High T$_{\\\\rm ex}$ & High gas/solid, High\\n & GL 2591, \\\\\\\\\\nenvelope & & (CH$_3$OH) & T$_{\\\\rm ex}$, Heated ices \\n & GL 2136 \\\\\\\\\\n & & & (C$_2$H$_2$, H$_2$O, CO$_2$) \\\\\\\\\\n\\\\noalign{\\\\smallskip}\\nHot core & High-T chemistry & Complex organics & Hydrides & Orion hot core, \\\\\\\\\\n & & (CH$_3$OCH$_3$, CH$_3$CN, & (OH, H$_2$O) \\n& SgrB2(N),G34.3 \\\\\\\\\\n&&vib.\\\\ excited mol.) && W~3(H$_2$O) \\\\\\\\\\n\\\\noalign{\\\\smallskip}\\nOutflow: & Shock chemistry, & Si- and S-species & \\n Atomic lines, Hydrides & W~3 IRS5, \\\\\\\\\\nDirect impact &Sputtering & (SiO, SO$_2$) &([S I], H$_2$O) & SgrB2(M) \\\\\\\\\\n\\\\noalign{\\\\smallskip}\\nPDR, Compact & Photodissociation,& Ions, radicals & Ionic lines, PAHs\\n& S~140, \\\\\\\\\\nH~II regions & Photoionization & (CN/HCN, CO$^+$) &([NeII], [CII])\\n& W~3 IRS4 \\\\\\\\\\n \\n%\\\\noalign{\\\\vspace{-0.8cm}}\\n\\\\tableline\\n\\\\end{tabular}\\n\\\\end{center}\\n\\\\end{table}\\n\\n\\nTable~1 summarizes the chemical characteristics of the\\nvarious physical components, together with the observational\\ndiagnostics at submillimeter and infrared wavelengths. \\nWithin the single-dish submillimeter and ISO beams,\\nmany of these components are blended together and interferometer\\nobservations will be essential to disentangle them. Nevertheless, the\\nsingle-dish data are useful because they encompass the entire envelope\\nand highlight the dominant component in the beam. Combined\\nwith the above chemical scenario, one may then attempt to establish an\\nevolutionary sequence of the sources.\\n\\nThe physical distinction between the `hot core' and the warm\\ninner envelope listed in Table~1 is currently not clear: does the `hot\\ncore' represent a separate physical component or is it simply the\\ninner warm envelope at a different stage of chemical evolution? Even\\nfrom an observational point of view, there appear to be different\\ntypes of `hot cores': some of them are internally heated by the young\\nstar (e.g., W~3(H$_2$O)), whereas others may just be dense clumps of\\ngas heated externally (e.g., the Orion compact ridge). This point\\nwill be further discussed in \\\\S\\\\S 4 and 5. Disks are not included in\\nTable~1, because little is known about their chemical characteristics,\\nor even their existence, around high-mass YSOs (see Norris, this\\nvolume).\\n\\n\\n\\\\section{Intermediate-Mass YSOs}\\n\\nIntermediate-mass pre-main sequence stars, in particular the so-called\\nHerbig Ae/Be stars, have received increased observational attention in\\nrecent years (see Waters \\\\& Waelkens 1998 for a review). These stars\\nhave spectral type A or B and show infrared excesses due to \\ncircumstellar dust. Typical luminosities are in the range $10^2 -\\n10^4$ L$_{\\\\odot}$, and several objects have been located within 1 kpc\\ndistance. Systematic mapping of CO and the submillimeter continuum of\\na sample of objects has been performed by Fuente et al.\\\\ (1998) and\\nHenning et al.\\\\ (1998). The data show the dispersion of the envelope\\nwith time starting from the deeply embedded phase (e.g.,\\nLkH$\\\\alpha$234) to the intermediate stage of a PDR (e.g., HD 200775\\nilluminating the reflection nebula NGC 7023) to the more evolved stage\\nwhere the molecular gas has disappeared completely (e.g., HD 52721).\\nThe increasing importance of photodissociation in the chemistry is\\nprobed by the increase in the CN/HCN abundance ratio. This ratio has\\nbeen shown in other high-mass sources to be an excellent tracer of\\nPDRs (e.g., Simon et al. 1997, Jansen et al.\\\\ 1995). Line surveys of\\nthese objects in selected frequency ranges would be useful to\\ninvestigate their chemical complexity, especially in the embedded\\nphase.\\n\\nISO-SWS observations of a large sample of Herbig Ae/Be stars have been\\nperformed by van den Ancker et al.\\\\ (2000b,c). In the embedded phase,\\nshock indicators such as [S I] 25.2 $\\\\mu$m are strong, whereas in the\\nlater phases PDR indicators such as PAHs are prominent. An excellent\\nexample of this evolutionary sequence is provided by three Herbig Ae\\nstars in the BD+40$^o$4124 region ($d\\\\approx 1$ kpc). The data\\nsuggest that in the early phases, the heating of the envelope is\\ndominated by shocks, whereas in later phases it is controlled by\\nultraviolet photons.\\n\\n\\n\\\\begin{figure}[t]\\n\\\\vspace{-3.8cm}\\n\\\\plottwo{dishoeck_fig3a.ps}{dishoeck_fig3b.ps}\\n\\\\vspace{-0.3cm}\\n\\\\caption{Left: ISO-LWS spectra of the intermediate mass YSO \\nLkH$\\\\alpha$234, showing strong atomic fine-structure lines of\\n[C II] 158 $\\\\mu$m and [O~I] 63 $\\\\mu$m, but weak molecular CO and\\nOH lines. Right: CO excitation diagram, indicating the presence\\nof a warm ($T\\\\approx 200-900$~K), dense ($n>10^5$ cm$^{-3}$) \\nregion (from:\\nGiannini et al.\\\\ 2000).}\\n\\\\label{fig-3}\\n\\\\vspace{-0.5cm}\\n\\\\end{figure}\\n\\n\\nISO-LWS data have been obtained for a similar sample of Herbig Ae/Be\\nstars by Lorenzetti et al.\\\\ (1999) and Giannini et al.\\\\ (2000), and\\nare summarized by Saraceno et al.\\\\ (1999). The [C II] 158 $\\\\mu$m and\\n[O I] 63 and 145 $\\\\mu$m lines are prominent in many objects and are\\ndue primarily to the PDR component in the large LWS beam ($\\\\sim\\n80''$). High-$J$ CO and OH far-infrared lines have been detected in\\nsome objects and indicate the presence of a compact, high temperature\\nand density region of $\\\\sim$1000 AU in size, presumably tracing the\\ninner warm envelope (see Figure~3).\\nFar-infrared lines of H$_2$O are seen in low-mass YSO spectra, but are\\nweak or absent in those of intermediate- and high-mass YSOs, with the\\nexception of Orion-KL and SgrB2 (e.g., Harwit et al.\\\\ 1998, Cernicharo\\net al.\\\\ 1997, Wright et al.\\\\ 2000). The absence of H$_2$O lines in\\nhigher-mass objects may be partly due to the larger distance of these\\nobjects, resulting in substantial dilution in the LWS beam. However,\\nphotodissociation of H$_2$O to OH and O by the enhanced ultraviolet radiation\\nmay also play a role.\\n\\nIn summary, both the submillimeter and infrared diagnostics reveal an\\nevolutionary sequence from the youngest `Group I' objects to `Group\\nIII' objects (cf.\\\\ classification by Fuente et al.\\\\ 1998), in which\\nthe envelope is gradually dispersed. Such a sequence is analogous to\\nthe transition from embedded Class 0/I objects to more evolved Class\\nII/III objects in the case of low-mass stars (Adams et al.\\\\ 1987). The\\nISO data provide insight into the relative importance of the heating\\nand removal mechanisms of the envelope. At the early stages of\\nintermediate-mass star formation, shocks due to outflows appear to\\ndominate whereas at later stages radiation is more important.\\n\\n\\\\section{Embedded, Infrared-Bright Massive YSOs}\\n\\n\\\\subsection{Sample}\\n\\nThe availability of complete, high quality ISO spectra for a\\nsignificant sample of massive young stars provides a unique\\nopportunity to study these sources through a combination of infrared\\nand submillimeter spectroscopy, and further develop these diagnostics.\\nVan der Tak et al.\\\\ (2000a) have selected a set of $\\\\sim$10 deeply\\nembedded massive YSOs which are bright at mid-infrared wavelengths (12\\n$\\\\mu$m flux $>$ 100 Jy), have luminosities of $10^3 - 2\\\\times 10^5$\\nL$_{\\\\odot}$ and distances $d\\\\leq$4 kpc. The sources are all in an\\nearly evolutionary state (comparable to the `Class 0/I' or `Group I'\\nstages of low- and intermediate-mass stars), as indicated by their\\nweak radio continuum emission and absence of ionic lines and PAH\\nfeatures. In addition to ISO spectra, JCMT submillimeter data and\\nOVRO interferometer observations have been obtained. For most of the\\nobjects high spectral resolution ground-based infrared data of CO,\\n$^{13}$CO and H$_3^+$ are available (Mitchell et al.\\\\ 1990, Geballe \\\\&\\nOka 1996, McCall et al.\\\\ 1999), and occasionally H$_2$ (Lacy et\\nal.\\\\ 1994, Kulesa et al.\\\\ 1999). For comparison, 5 infrared-weak\\nsources with similar luminosities are studied at submillimeter\\nwavelengths only. This latter set includes hot cores and ultracompact\\nH~II regions such as W~3(H$_2$O), IRAS 20126+4104 (Cesaroni et al.\\\\ \\n1997, 1999), and NGC~6334 IRS1.\\n\\n\\\\subsection{Physical structure of the envelope}\\n\\nIn order to derive molecular abundances from the observations, a good\\nphysical model of the envelope is a prerequisite. Van der Tak et al.\\\\ \\n(1999, 2000a) outline the techniques used to constrain the temperature\\nand density structure (Figure~4). The total mass within the\\nbeam is derived from submillimeter photometry, whereas the size scale\\nof the envelope is constrained from line and continuum maps. The dust\\nopacity has been taken from Ossenkopf \\\\& Henning (1994) and yields\\nvalues for the mass which are consistent with those derived from\\nC$^{17}$O for warm sources where CO is not depleted\\nonto grains.\\n\\n\\n\\\\begin{figure}[t]\\n\\\\plotfiddle{dishoeck_fig4.ps}{7.7cm}{0}{45}{45}{-120}{-60}\\n\\\\caption{Overview of method used for constraining the temperature and density\\nstructure of envelopes. A power-law density structure with trial values\\nfor the exponent\\n$\\\\alpha_i$ and molecular abundances $X_j$ is adopted\\n(based on: van der Tak et al.~2000a).}\\n\\\\label{fig-4}\\n\\\\end{figure}\\n\\n\\nThe temperature structure of the dust is calculated taking the\\nobserved luminosity of the source, given a power-law density structure\\n(see below). At large distances from the star, the temperature follows\\nthe optically thin relation $\\\\propto r^{-0.4}$, whereas at smaller\\ndistances the dust becomes optically thick at infrared wavelengths and\\nthe temperature increases more steeply (see Figure~5). It is assumed\\nthat $T_{\\\\rm gas}=T_{\\\\rm dust}$, consistent with explicit calculations\\nof the gas and dust temperatures by, e.g., Doty \\\\& Neufeld (1997)\\nfor these high densities.\\n\\nThe continuum data are sensitive to temperature and column density,\\nbut not to density. Observations of a molecule with a large dipole\\nmoment are needed to subsequently constrain the density structure. One\\nof the best choices is CS and its isotope C$^{34}$S, for which lines\\nranging from $J$=2--1 to 10--9 have been observed. Assuming a\\npower-law density profile $n(r)= n_o (r/r_o)^{-\\\\alpha}$, values of\\n$\\\\alpha$ can be determined from minimizing $\\\\chi^2$ between the CS\\nline data and excitation models. The radiative transfer in the lines\\nis treated through a Monte-Carlo method. The best fit to the data on\\nthe infrared-bright sources is obtained for $\\\\alpha = 1.0 - 1.5$,\\nwhereas the hot core/compact H~II region sample requires higher\\nvalues, $\\\\alpha \\\\approx 2$. This derivation assumes that the CS\\nabundance is constant through the envelope; if it increases with\\nhigher temperatures, such as may be the case for hot cores, the values\\nof $\\\\alpha$ are lowered. Note that the derived values of\\n$\\\\alpha=1.0-1.5$ are lower than those found for deeply embedded\\nlow-mass objects, where $\\\\alpha\\\\approx 2$ (e.g., Motte et al.\\\\ 1998,\\nHogerheijde et al.\\\\ 1999).\\n\\n\\\\begin{figure}[t]\\n\\\\plotfiddle{dishoeck_fig5.ps}{7.0cm}{-90}{45}{45}{-170}{260}\\n\\\\vspace{-0.3cm}\\n\\\\caption{Derived temperature and density structure for the envelope\\naround the massive YSO\\nGL 2591 (L=$2\\\\times 10^4$ L$_{\\\\odot}$, $d$=1 kpc). \\nThe critical densities of the CS 2--1 and 10--9 lines are\\nindicated, as are the typical beam sizes of the JCMT \\nat 345 GHz and OVRO at 100 GHz (based on: van der Tak et \\nal.\\\\ 1999).}\\n\\\\label{fig-5}\\n\\\\vspace{-0.5cm}\\n\\\\end{figure}\\n\\n\\nFigure 5 displays the derived temperature and density structure\\nfor the source GL 2591, together with the sizes of the JCMT and\\nOVRO beams. While the submillimeter data are weighted toward the\\ncolder, outer envelope, the infrared absorption line observations sample\\na pencil-beam line of sight toward the YSO and are more sensitive to\\nthe inner warm ($\\\\sim 1000$~K) region. On these small scales, the\\nenvelope structure deviates from a radial power law, which decreases\\nthe optical depth at near-infrared wavelengths by a factor of \\n$\\\\sim 3$ (van der Tak et al.\\\\\\n1999).\\n\\n\\nFor sources for which interferometer data are available, unresolved\\ncompact continuum emission is detected on scales of a few thousand AU\\nor less. This emission is clearly enhanced compared with that\\nexpected from the inner ``tip'' of the power-law envelope, and its\\nspectral index indicates optically thick warm dust, most likely in a\\ndense circumstellar shell or disk. The presence of this shell or disk\\nis also indicated by the prevalence of blue-shifted outflowing dense\\ngas without a red-shifted counterpart on $< 10''$ scales.\\n\\n\\n\\\\subsection{Chemical structure: infrared absorption lines}\\n\\nThe ISO-SWS spectra of the infrared-bright sources show absorption by\\nvarious gas-phase molecules, in addition to strong features by ices.\\nMolecules such as CO$_2$ (van Dishoeck et al.\\\\ 1996,\\nBoonman et al.\\\\ 1999, 2000a), H$_2$O (van Dishoeck \\\\& Helmich 1996, Boonman\\net al.\\\\ 2000b), CH$_4$ (Boogert et al.\\\\ 1998), HCN and C$_2$H$_2$\\n(Lahuis \\\\& van Dishoeck 2000) have been detected (see also van\\nDishoeck 1998, Dartois et al.\\\\ 1998).\\n\\nIn the infrared, absorption out of all $J$-levels is observed in a\\nsingle spectrum. The excitation temperatures $T_{\\\\rm ex}$ of the\\nvarious molecules, calculated assuming LTE, range from $\\\\ltsim 100$ to\\n$\\\\sim 1000$~K between sources, giving direct information on \\nthe physical component in which the molecules reside. While CO \\nis well-mixed throughout the envelopes, H$_2$O, HCN and C$_2$H$_2$ are\\nenhanced at high temperatures. In contrast, CO$_2$ seems to avoid the\\nhottest gas. High spectral resolution ground-based data of HCN and\\nC$_2$H$_2$ by Carr et al.\\\\ (1995) and Lacy et al.\\\\ (1989) for a few\\nobjects suggest line widths of at most a few km s$^{-1}$, excluding an\\norigin in outflowing gas.\\n\\nThe abundances of H$_2$O, HCN and C$_2$H$_2$ increase by factors of\\n$\\\\gtsim 10$ with increasing $T_{\\\\rm ex}$ (see Figure~7). The warm\\nH$_2$O must be limited to a $\\\\ltsim 1000$~AU region, since the pure\\nrotational lines are generally not detected in the $80''$ ISO-LWS beam\\n(Wright et al.\\\\ 1997). For CO$_2$, the abundance variation between\\nsources is less than a factor of 10, and no clear trend with $T_{\\\\rm\\n ex}$ is found. For the same sources, the H$_2$O and CO$_2$ ice\\nabundances show a decrease by an order of magnitude, consistent with\\nevaporation of the ices. However, the gas-phase H$_2$O and CO$_2$\\nabundances are factors of $\\\\sim 10$ lower than expected if all\\nevaporated molecules stayed in the gas phase, indicating that\\nsignificant chemical processing occurs after evaporation. More\\ndetailed modeling using the source structures derived from\\nsubmillimeter data is in progress.\\n\\n\\\\begin{figure}[t]\\n\\\\plotfiddle{dishoeck_fig6.ps}{6.8cm}{-90}{50}{50}{-210}{260}\\n\\\\caption{{\\\\it Left:}~Abundance of HCN,\\n$N$(HCN)/$N_{\\\\rm tot}$(H$_2$), as a function of the\\n$^{13}$CO excitation temperature measured by\\nMitchell et al.\\\\ (1990). {\\\\it Middle:} Abundance of H$_2$O in the warm gas\\n$N$(H$_2$O)/$N_{\\\\rm warm}$(H$_2$) as a function of $^{13}$CO excitation\\ntemperature;\\n{\\\\it Right:}~Abundance of H$_2$O ice as a function of\\n$^{13}$CO excitation temperature. The same trend\\nis found if the dust temperature, as derived from the 45/100 $\\\\mu$m\\nflux, is used (based on: Lahuis \\\\& van Dishoeck 2000; van Dishoeck 1998).}\\n\\\\label{fig-6}\\n\\\\end{figure}\\n\\n\\n\\\\subsection{Chemical structure: submillimeter emission}\\n\\nThe JCMT data of the infrared-bright objects show strong lines, but\\nlack the typical crowded `hot core' spectra observed for objects such\\nas W~3(H$_2$O) and NGC 6334 IRS1. Complex organics such as\\nCH$_3$OCH$_3$ and CH$_3$OCHO are detected in some sources (e.g., GL\\n2591, NGC 7538 IRS1), but are not as prominent as in the comparison\\nsources. Yet warm gas is clearly present in these objects.\\nIs the `hot core' still too small to be picked up by the\\nsingle dish beams, or are the abundances of these molecules not (yet)\\nenhanced?\\n\\nTo investigate this question, \\nvan der Tak et al.\\\\ (2000b) consider the analysis of\\ntwo species, H$_2$CO and CH$_3$OH. Both\\nspecies have many lines throughout the submillimeter originating from\\nlow- and high-lying energy levels. Given the physical structure\\ndetermined in \\\\S 4.2, abundance {\\\\it profiles} can be constrained. Two\\nextreme, but chemically plausible models are considered: (i) a model\\nwith a constant abundance throughout the envelope. This model is\\nmotivated by the fact that pure gas-phase reaction schemes do not show\\nlarge variations in calculated abundances between 20 and 100~K; (ii) a\\nmodel in which the abundance `jumps' to a higher value at the ice\\nevaporation temperature, $T_d\\\\approx 90$~K. In this model, the\\nabundances in the outer envelope are set at those observed in cold\\nclouds, so that the only free parameter is the amount of abundance\\nincrease.\\n\\nIt is found that the H$_2$CO data can be well fit with a constant\\nabundance of a few $\\\\times 10^{-9}$ throughout the envelope. However,\\nthe high $J,K$ data for CH$_3$OH require a jump in its abundance from\\n$\\\\sim 10^{-9}$ to $\\\\sim 10^{-7}$ for the warmer sources. This is\\nconsistent with the derived excitation temperatures: H$_2$CO has a\\nrather narrow range of $T_{\\\\rm ex}$=50--90~K, whereas CH$_3$OH shows\\n$T_{\\\\rm ex}$=30--200~K. Moreover, the interferometer maps of CH$_3$OH\\nrule out constant abundance models. The jump observed for CH$_3$OH is\\nchemically plausible since this molecule is known to be present in icy\\ngrain mantles with abundances of 5--40\\\\% with respect to H$_2$O ice,\\ni.e., $\\\\sim 10^{-7}-10^{-6}$ w.r.t.\\\\ H$_2$. Similar increases in the\\nabundances of organic molecules (e.g., CH$_3$OH, C$_2$H$_3$CN, ....)\\nare found with increasing $T_{\\\\rm dust}$ for a set of `hot--core'\\nobjects by Ikeda \\\\& Ohishi (1999).\\n\\n\\n\\\\subsection{Comparison with chemical models}\\n\\nBoth the infrared and submillimeter data show increases in the\\nabundances of various molecules with increasing temperature. Four\\ntypes of species can be distinguished: (i) `passive' molecules which\\nare formed in the gas phase, freeze out onto grains during the cold\\n(pre-)collapse phase and are released during warm-up without chemical\\nmodification (e.g., CO, C$_2$H$_2$); (ii) molecules which are formed\\non the grains during the cold phase by surface reactions and are\\nsubsequently released into the warm gas (e.g., CH$_3$OH); (iii)\\nmolecules which are formed in the warm gas by gas-phase reactions with\\nevaporated molecules (e.g., CH$_3$OCH$_3$); (iv) molecules which are\\nformed in the hot gas by high temperature reactions (e.g., HCN). These\\ntypes of molecules\\nare associated with characteristic temperatures of (a) $T_{\\\\rm\\n dust}<20$~K, where CO is frozen out; the presence of CO ice is\\nthought to be essential for the formation of CH$_3$OH; (b) $T_{\\\\rm\\n dust} \\\\approx 90$~K, where all ices evaporate on a time scale of\\n$<10^5$ yr; and (c) $T_{\\\\rm gas}>230$~K, where gas-phase reactions\\ndrive the available atomic oxygen into water through the reactions O +\\nH$_2$ $\\\\to$ OH $\\\\to$ H$_2$O (Ceccarelli et al.\\\\ 1996, Charnley 1997).\\nAtomic oxygen is one of the main destroyers of radicals and carbon\\nchains, so that its absence leads to enhanced abundances of species\\nlike HCN and HC$_3$N in hot gas.\\n\\nWater is abundantly formed on the grains, but the fact that the\\nH$_2$O abundance in the hot gas is not as large as that of the ices\\nsuggests that H$_2$O is broken down to O and OH after evaporation by\\nreactions with H$_3^+$. H$_2$O can subsequently be reformed in warm\\ngas at temperatures above $\\\\sim$230~K, but Figure~7 indicates that not\\nall available gas-phase oxygen is driven into H$_2$O, as the models\\nsuggest. The low abundance of CO$_2$ in the warm gas is still a\\npuzzle, since evaporation of abundant CO$_2$ ice is observed. The\\nmolecule must be broken down rapidly in the warm gas, with no\\nreformation through the CO + OH $\\\\to$ CO$_2$ reaction (see question by\\nMinh).\\n\\n\\\\subsection{Evolution?}\\n\\nThe objects studied by van der Tak et al.\\\\ (2000a) are all in an early\\nstage of evolution, when the young stars are still deeply embedded in\\ntheir collapsing envelope. Nevertheless, even within this narrow\\nevolutionary range, there is ample evidence for physical and chemical\\ndifferentiation of the sources. This is clearly traced by the\\nincrease in the gas/solid ratios, the increase in abundances of several\\nmolecules, the decrease in the ice abundances, and the increase\\nof the amount of crystalline ice with increasing temperature\\n(Boogert et al.\\\\ 2000a).\\n\\nThe fact that the various indicators involve different\\ncharacteristic temperatures ranging from $<$50 K (evaporation of\\napolar ices) to 1000 K ($T_{\\\\rm ex}$ of gas-phase molecules)\\nindicates that the heating is not a local effect, but that `global\\nwarming' occurs throughout the envelope. Moreover, it cannot be a\\ngeometrical line-of-sight effect in the mid-infrared data, since the\\nfar--infrared continuum (45/100 $\\\\mu$m) and submillimeter line data\\n(CH$_3$OH) show the same trend. Shocks with different filling factors\\nare excluded for the same reason.\\n\\nCan we relate this `global warming' of the envelope to an evolutionary\\neffect, or is it determined by other factors? The absence of a\\ncorrelation of the above indicators with luminosity or mass of the\\nsource argues against them being the sole controlling factor. The\\nonly significant trend is found with the ratio of envelope mass over\\nstellar mass. The physical interpretation of such a relation would be\\nthat with time, the envelope is dispersed by the star, resulting in a\\nhigher temperature throughout the envelope.\\n\\n\\\\section{Outstanding questions and future directions}\\n\\nThe results discussed here suggest that the observed chemical abundance and\\ntemperature variations can indeed be used to trace the evolution of\\nthe sources, and that, as in the case of low- and intermediate-mass\\nstars, the dispersion of the envelope plays a crucial role. \\nThe combination of infrared and submillimeter diagnostics\\nis very important in the analysis. An\\nimportant next step would be to use these diagnostics to probe a much\\nwider range of evolutionary stages for high-mass stars, especially in\\nthe hot core and (ultra-)compact H II region stages, to develop a more\\ncomplete scenario of high-mass star formation. The relation between\\nthe inner warm envelope and the `hot core' is still uncertain: several\\nobjects have been observed which clearly have hot gas and evaporated\\nices (including CH$_3$OH) in their inner regions, but which do not\\nshow the typical crowded `hot core' submillimeter spectra. Are these\\nobjects just on their way to the `hot core' chemical phase? Or is the\\n`hot core' a separate physical component, e.g., a dense shell at the\\nedge of the expanding hyper-compact H~II region due to the pressure\\nfrom the ionized gas, which is still too small to be\\npicked up by the single-dish beams? In either case, time or evolution\\nplays a role and would constrain the ages of the infrared-bright\\nsources to less than a few $\\\\times 10^4$ yr since evaporation.\\nInterferometer data provide evidence for the presence of a separate\\nphysical component in the inner 1000 AU, but lack the spatial\\nresolution to distinguish a shell from any remnant disk, for example\\non kinematic grounds. \\n\\nAn important difference between high- and low-mass objects may be the\\nmechanism for the heating and dispersion of their envelopes. For\\nlow-mass YSOs, entrainment of material in outflows is the\\ndominant process (Lada 1999). For intermediate-mass stars, outflows\\nare important in the early phase, but ultraviolet radiation\\nbecomes dominant in the later stages (see \\\\S~3). The situation for\\nhigh-mass stars is still unclear. The systematic increase in\\ngas/solid ratios and gas-phase abundances point to global heating of\\nthe gas and dust, consistent with a radiative mechanism. However, a\\nclear chemical signature of ultraviolet radiation on gas-phase species\\nand ices in the embedded phase has not yet been identified, making it\\ndifficult to calibrate its effect. On the other hand, high-mass stars\\nare known to have powerful outflows and winds, but a quantitative\\ncomparison between their effectiveness in heating an extended part\\nof the envelope and removing material is still\\nlacking. Geometrical effects are more important in less embedded\\nsystems, as is the case for low-mass stars, where the circumstellar\\ndisk may shield part of the envelope from heating (Boogert et al.\\\\ \\n2000b).\\n\\n\\nTo what extent does the chemical evolution picture also apply to\\nlow-mass stars? Many of the chemical processes and characteristics\\nlisted in Table~1 are also known to occur for low-mass YSOs, but\\nseveral important diagnostic tools are still lacking. In particular,\\nsensitive mid-infrared spectroscopy is urgently needed to trace the evolution\\nof the ices for low-mass YSOs and determine gas/solid ratios. Also,\\nmolecules as complex as CH$_3$OCH$_3$ and C$_2$H$_5$CN have not yet\\nbeen detected toward low-mass YSOs, although the limits are not very\\nstringent (e.g., van Dishoeck et al.\\\\ 1995). Evaporation of ices\\nclearly occurs in low-mass environments as evidenced by enhanced\\nabundances of grain-surface molecules in shocks (e.g., Bachiller \\\\&\\nP\\\\'erez-Guti\\\\'errez 1997), but whether a similar `hot core' chemistry\\nensues is not yet known. Differences in the \\nH/H$_2$ ratio and temperature structure in the (pre-)collapse\\nphase may affect the\\ngrain-surface chemistry and the ice composition,\\nleading to different abundances of solid CH$_3$OH, which \\nis an essential ingredient\\nfor building complex molecules.\\n\\nFuture instrumentation with high spatial resolution ($< 1''$) and\\nhigh sensitivity will be essential to make progress in our\\nunderstanding of the earliest phase of massive star formation, in\\nparticular the SMA and ALMA at submillimeter wavelengths, and SIRTF,\\nSOFIA, FIRST and ultimately NGST at mid- and far-infrared wavelengths.\\n\\n\\n\\n\\\\acknowledgments\\n\\nThe authors are grateful to G.A. Blake, A.C.A.\\\\ Boogert, A.M.S.\\\\ Boonman, P.\\\\ \\nEhrenfreund, N.J.\\\\ Evans, T.\\\\ Giannini, F.\\\\ Lahuis, L.G.\\\\ Mundy, A.\\\\ \\nNummelin, W.A.\\\\ Schutte, A.G.G.M.\\\\ Tielens, and M.E.\\\\ van den Ancker\\nfor discussions, collaborations and figures. 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(Berlin: Springer), p.\\\\ 279\\n\\n\\\\reference\\nSchilke, P., Groesbeck, T.D., Blake, G.A., \\\\& Phillips, T.G.\\\\ 1997,\\nApJS, 108, 301\\n\\n\\n\\\\reference\\nSimon, R., Stutzki, J., Sternberg, A., \\\\& Winnewisser, G.\\\\ 1997,\\nA\\\\&A, 327, L9\\n\\n\\\\reference\\nSutton, E.C., Jaminet, P.A., Danchi, W.C., \\\\& Blake, G.A.\\\\ 1991,\\nApJS, 77, 255\\n\\n\\\\reference\\nSutton, E.C., Peng, R., Danchi, W.C., et al.\\\\ 1995, ApJS, 97, 455\\n\\n\\\\reference\\nTurner, B.E.\\\\ 1991, ApJS, 76, 617\\n\\n\\\\reference\\nvan den Ancker, M. et al.\\\\ 2000a, A\\\\&A, submitted\\n\\n\\\\reference\\nvan den Ancker, M. et al.\\\\ 2000b, A\\\\&A, in press\\n\\n\\\\reference\\nvan den Ancker, M. et al.\\\\ 2000c, A\\\\&A, submitted\\n\\n\\\\reference\\nvan der Tak, F.F.S., van Dishoeck, E.F., Evans, N.J., Bakker, E.J., \\\\&\\nBlake, G.A.\\\\ 1999, ApJ, 522, 991\\n\\n\\\\reference\\nvan der Tak, F.F.S., van Dishoeck, E.F., Evans, N.J., \\\\& Blake, G.A.\\\\ 2000a,\\nApJ, in press\\n\\n\\\\reference\\nvan der Tak, F.F.S.\\\\ \\\\& van Dishoeck, E.F.\\\\ 2000b,\\nA\\\\&A, to be submitted\\n\\n\\\\reference\\nvan Dishoeck, E.F.\\\\ 1998, Far.\\\\ Disc., 109, 31\\n\\n\\\\reference\\nvan Dishoeck, E.F. \\\\& Blake, G.A.\\\\ 1998, ARAA, 36, 317\\n\\n\\n\\\\reference\\nvan Dishoeck, E. F., Blake, G. A., Jansen, D. J. \\\\& Groesbeck, T. D. 1995, \\n\\\\apj, 447, 760 \\n\\n\\\\reference\\nvan Dishoeck, E.F. \\\\& Helmich, F.P. 1996, A\\\\&A, 315, L177\\n\\n\\\\reference\\nvan Dishoeck, E.F., Helmich, F.P., de Graauw, Th. et al. 1996,\\nA\\\\&A, 315, L349\\n\\n\\\\reference\\nvan Dishoeck, E.F. \\\\& Hogerheijde, M.R. 1999, in Origin of Stars and Planetary\\nSystems,\\neds.\\\\ C.J.\\\\ Lada and N.\\\\ Kylafis (Dordrecht:\\nKluwer), p.\\\\ 97\\n\\n\\\\reference\\nvan Dishoeck, E.F. et al.\\\\ 1999, in The Universe as seen by ISO,\\neds.\\\\ P.\\\\ Cox and M.F.\\\\ Kessler (Noordwijk: ESTEC), ESA SP-427, p.\\\\ 437\\n\\n\\n\\\\reference\\nWaters, L.B.F.M.\\\\ \\\\& Waelkens, C.\\\\ 1998, ARAA, 36, 233\\n\\n\\n\\\\reference\\nWright, C.M., van Dishoeck, E.F., Helmich, F.P., Lahuis, F., Boogert, A.C.A.,\\n\\\\& de Graauw, Th. 1997, \\nin First ISO Workshop on Analytical Spectroscopy,\\nESA SP-419, p. 37\\n\\n\\\\reference\\nWright, C.M., van Dishoeck, E.F., Black, J.H., Feuchtgruber, H.,\\nCernicharo, J., Gonz\\\\'alez-Alfonso, E., \\\\& de Graauw,\\nTh.\\\\ 2000, A\\\\&A, in press \\n\\n\\\\end{references}\\n\\n\\n\\\\begin{question}{M.\\\\ Ohishi}\\nI agree with the point you mentioned, that the chemical differences among\\nhot cores is due to a difference of evolutionary stage. Now we have\\nseveral well-known hot cores such as Orion KL/S, W~3 IRS5/H$_2$O/IRS4,\\nSgrB2 N/M/NW etc. Can you give us your personal view on the evolutionary\\ndifferences of these sources?\\n\\\\end{question} \\n\\n\\\\begin{answer}{E.F.\\\\ van Dishoeck}\\nVan der Tak et al.\\\\ (2000a) argue that the infrared-bright objects such as W~3\\nIRS5 represent an earlier evolutionary phase than the hot cores, on the basis\\nof an anti-correlation with the radio continuum. The physical picture is that\\nthe ionizing UV radiation and stellar winds push the hottest dust in the inner\\nregions further out, decreasing the temperature of the dust and thus the\\nnear-infrared continuum. At the same time, the size of the region which can be\\nionized is increased. The `erosion' of the envelopes thus occurs from the\\ninside out. For other sources, infrared diagnostics are lacking, so that the\\nsituation is less clear. It would be great if chemistry could help to tie down\\nthe time scales of the various phases.\\n\\\\end{answer}\\n\\n\\\\begin{question}{W.\\\\ Irvine}\\nHow do you interpret the behavior of the PAH features as a function of\\nevolutionary stage in the sources that you discussed?\\n\\\\end{question}\\n\\n\\\\begin{answer}{E.F.\\\\ van Dishoeck}\\nThe absence of PAH features in the early embedded stage can be due either\\nto a lack of ultraviolet radiation to excite the features or to an absence\\nof the carriers. Manske \\\\& Henning (1999, A\\\\&A 349, 907) have argued \\nfor the case of Herbig Ae/Be stars that\\nthere should be sufficient radiation to excite PAHs in the envelope/disk\\nsystem,\\nso that the lack is likely due to the absence of the PAHs\\nthemselves. Perhaps the PAHs have accreted into the icy mantles at the\\nhigh densities in the inner envelope and do not evaporate\\nand/or are chemically transformed into\\nother more refractory species on grains. Alternatively, the region producing\\nultraviolet radiation (H~II region) may be very small \\nin these massive objects, and the photons may not reach the PAH-rich\\nmaterial or have a very small beam filling factor.\\nOnce the envelope breaks up and\\nultraviolet radiation can escape to the less dense\\nouter envelope, the PAH features from those\\nregions will appear in spectra taken with large beams.\\n\\\\end{answer}\\n\\n\\\\begin{question}{T.\\\\ Geballe}\\nYou said that there is little evidence of the effect of ultraviolet radiation\\non solid-state chemistry. Isn't the 4.6 $\\\\mu$m XCN feature a good example\\nof that influence?\\n\\\\end{question}\\n\\n\\\\begin{answer}{E.F.\\\\ van Dishoeck}\\nThe `XCN' feature is indeed the best candidate for tracing the \\nultraviolet processing\\nof ices. If ascribed to OCN$^-$, it likely involves HNCO as\\na precursor. In the laboratory, HNCO is produced by photochemical\\nreactions of CO and NH$_3$, but in the interstellar medium grain surface\\nchemistry is an alternative possibility which does not necessarily\\ninvolve ultraviolet radiation (see Ehrenfreund \\\\& Schutte,\\nthis volume). \\n\\\\end{answer}\\n\\n\\\\begin{question}{Y.C.\\\\ Minh}\\nDo you have an explanation of the low and constant abundances of CO$_2$\\nin the gas phase?\\n\\\\end{question}\\n\\n\\\\begin{answer}{E.F.\\\\ van Dishoeck}\\nCharnley \\\\& Kaufman (2000, ApJ, 529, L111) argue that the evaporated CO$_2$ is\\ndestroyed by reactions with atomic hydrogen at high temperatures in shocks.\\nThis is an interesting suggestion, but needs to be tested against other\\nspecies such as H$_2$O and H$_2$S which can be destroyed by\\nreactions with atomic hydrogen as well. Also, the amount of material \\nin the envelope that can be affected by shocks is not clear.\\n\\\\end{answer}\\n\\n\\\\end{document}\\n\\n\\n\\n\"\n }\n]","isConversational":false},"bibtex":{"kind":"list like","value":[],"string":"[]","isConversational":false}}},{"rowIdx":98,"cells":{"paper_id":{"kind":"string","value":"astro-ph0002099"},"title":{"kind":"string","value":"Geodetic Precession and the Binary Pulsar B1913+16"},"authors":{"kind":"list like","value":[{"author":"A. Karastergiou"},{"author":"M. Kramer"},{"author":"N. Wex"},{"author":"A. von Hoensbroech"}],"string":"[\n {\n \"author\": \"A. Karastergiou\"\n },\n {\n \"author\": \"M. Kramer\"\n },\n {\n \"author\": \"N. Wex\"\n },\n {\n \"author\": \"A. von Hoensbroech\"\n }\n]","isConversational":false},"abstract":{"kind":"string","value":"A change of the component separation in the profiles of the binary pulsar PSR B1913+16 has been observed for the first time (Kramer 1998) as expected by geodetic precession. In this work we extend the previous work by accounting for recent data from the Effelsberg 100-m telescope and Arecibo Observatory and testing model predictions. We demonstrate how the new information will provide additional information on the solutions of the system geometry."},"latex":{"kind":"list like","value":[{"name":"contrib1.tex","string":"\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{Karastergiou, Kramer, Wex \\& von Hoensbroech}\n{Geodetic Precession and the Binary Pulsar B1913+16}\n\\pagestyle{myheadings}\n\\nofiles\n\n\\begin{document}\n\\title{Geodetic Precession and the Binary Pulsar B1913+16}\n\\author{A. Karastergiou, M. Kramer, N. Wex, A. von Hoensbroech}\n\\affil{\nMax Planck Institut f\\\"ur Radioastronomie, Auf dem H\\\"ugel 69, 53121 Bonn, Germany\n}\n\\begin{abstract}\nA change of the component separation in the profiles of the binary pulsar PSR B1913+16\nhas been observed for the first time (Kramer 1998) as\nexpected by geodetic precession.\nIn this work we extend the previous work by accounting\nfor recent data from the Effelsberg 100-m telescope and Arecibo Observatory\nand testing model predictions. We demonstrate how the new information will provide additional\ninformation on the solutions of the system geometry.\n\\end{abstract}\n\n\\vspace{-3ex}\n\n\\section{Introduction}\n\nThe binary pulsar PSR B1913+16 exhibits\na measurable amount of geodetic precession due to a misalignment of its\nspin axis and orbital angular momentum (relativistic spin orbit coupling) by an angle $\\delta$\n(see also Stairs et al., for geodetic precession in PSR B1534+12).\nThe angle between the line of sight and the spin axis, $\\zeta$, changes according to:\n\\begin{displaymath}\n\\cos\\zeta(t) = -\\cos\\delta\\cos i\n +\\sin\\delta\\sin i \\cos \\Omega_{{\\rm prec}} (t-T_0) \\;,\n\\end{displaymath}\nwhere $i$ is the orbital inclination of the binary system.\nGeneral Relativity (GR) predicts a rate of precession $\\Omega_{{\\rm prec}}=1.21$ deg yr$^{-1}$,\nleading to a change in the pulse profile and polarization characteristics with time.\n\\\\\nPrevious observations by Weisberg, Romani and Taylor (1989) detected\na change in the relative amplitude of the trailing and leading component, but no\nchange in the component separation. Also, there were no\nchanges in the position angle swing of the linear polarization noted (Cordes, Wasserman \\&\nBlaskiewicz 1990).\n\n\\section{Recent Observations Cast Some Light}\n\nThe evolution of the observed radio pulse profile of PSR B1913+16 would be\ndetermined when the four parameters\n$\\alpha, \\delta, \\rho, T_{0}$ were specified for a given $i$, where\n%\\begin{description}\n$\\alpha$ is the angle between the magnetic pole and the spin axis,\n$\\delta$ is as mentioned above,\n$\\rho$ is the angular radius of the emission cone and\n$T_{0}$ the epoch of precession.\n%\\end{description}\n\\nopagebreak\nBased on recent data from the Effelsberg 100-m telescope, Kramer (1998) first noticed a\nchange in the component separation $W$. This allows a solution region in parametric space\nthat respects GR and the\n{\\bf{\\underline{hollow cone model} (HCM)}}.\n\\begin{displaymath}\n W(t) = 2\\arccos\\left[\\frac{\\cos\\rho - \\cos\\alpha \\cos\\zeta(t)}\n {\\sin\\alpha \\sin\\zeta(t)}\\right] \n\\end{displaymath}\nEffelsberg polarization data has been used\nin respect with the \\underline{\\bf rotating vector} \\\\ \\underline{\\bf model} {\\bf(RVM)},\nto further narrow down the solution region.\n\\begin{displaymath}\n \\psi(t) = \\arctan\\left[\\frac{\\sin\\alpha\\sin(\\phi-\\phi_0)}\n {\\cos\\alpha \\sin\\zeta(t) - \\sin\\alpha\\cos\\zeta(t)}\\right] \\quad + const. \n\\end{displaymath}\n\nThe inclination of the binary orbit with respect to the line-of-sight, $i$,\nis known from timing observations modulo the ambiguity\n$i\\longrightarrow 180^\\circ - i$. The possibilities are:\nCase A: $i= 47.2^\\circ$, Case B: $i= 132.8^\\circ$ \n\n\\vspace{-2ex}\n\n\\section{The Solution Today}\n\n%\\parbox[t]{6cm}{\n\\begin{figure}[h]\n\\centerline{\n%\\hspace*{-1cm}\n\\epsfxsize=7cm\n\\epsfysize=7cm\n\\epsffile{fig.eps}\n%\\caption{The solutions for $\\alpha$ and $\\delta$ are found in the unshaded regions\n%within the areas confined by the black curves and the bounding box}\n\\hspace{0.25cm}\n\\parbox[b]{6cm}{\\sloppy\nFigure 1. {\\small The pulse component separation data (Effelsberg + Arecibo) in conjunction with the HCM\nwas used to produce a $\\chi^{2}$ area plot indicating the $3\\sigma$ confidence level\nsolutions for $\\alpha$ and $\\delta$, areas inside the surfaces traced by the black lines.\nAll possible solutions were then fed into the RVM to produce\nposition angle curves, which were compared to Effelsberg polarization data,\nonly allowing for solutions in the unshaded areas. So, the solution must be located on\na black surface\ninside an unshaded region (for detailed explanation of this figure check out \n{\\it http://www.mpifr-bonn.mpg.de/staff/akara/psr1913})\n}}}\n\\end{figure}\n\nThe set of plausible solutions has been well limited, as shown in Fig 1.\nThe inclination of the binary orbit is most likely to be Case B rather than Case A (Wex, Kalogera, Kramer\n2000). More precise use of the polarization data plus a molding of the\ntwo models (HCM \\& RVM) to specifically suit PSR B1913+16\n(see also Weisberg \\& Taylor in these proceedings)\ncould further limit the solutions and\nenable a prediction on the future of this system.\n\n\\vspace{-2ex}\n\n\\begin{references}\n\\vspace{-2ex}\n\\reference\nCordes,~J.M., Wasserman,~I., \\& Blaskiewicz,~M. 1990, \\apj, 349, 546\n\n\\reference\nDamour,~T., \\& Ruffini,~R. 1974, Acad. Sci. Paris, 279, s\\'erie A, 971\n\n\\reference\nDamour,~T., \\& Taylor,~J.H. 1992, Phys. Rev. D, 45, 1840\n\n\\reference\nHulse,~R.A., \\& Taylor,~J.H. 1975, \\apj, 195, L51\n\n\\reference\nKramer,~M. 1998, \\apj, 509, 856\n\n\\reference\nTaylor,~J.H. 1999, Proceedings of the XXXIV'th Rencontres de Moriond, to be published\n\n\\reference\nWeisberg,~J.M., Romani,~R., \\& Taylor,~J.H. 1989, \\apj, 347, 1029\n\n\\reference\nWex,~N., Kalogera,~V., Kramer,~M. 2000, \\apj, 528, 401\n\n\\end{references}\n\n\\end{document}\n\n\n"}],"string":"[\n {\n \"name\": \"contrib1.tex\",\n \"string\": \"\\\\documentstyle[11pt,newpasp,twoside,epsf]{article}\\n\\\\markboth{Karastergiou, Kramer, Wex \\\\& von Hoensbroech}\\n{Geodetic Precession and the Binary Pulsar B1913+16}\\n\\\\pagestyle{myheadings}\\n\\\\nofiles\\n\\n\\\\begin{document}\\n\\\\title{Geodetic Precession and the Binary Pulsar B1913+16}\\n\\\\author{A. Karastergiou, M. Kramer, N. Wex, A. von Hoensbroech}\\n\\\\affil{\\nMax Planck Institut f\\\\\\\"ur Radioastronomie, Auf dem H\\\\\\\"ugel 69, 53121 Bonn, Germany\\n}\\n\\\\begin{abstract}\\nA change of the component separation in the profiles of the binary pulsar PSR B1913+16\\nhas been observed for the first time (Kramer 1998) as\\nexpected by geodetic precession.\\nIn this work we extend the previous work by accounting\\nfor recent data from the Effelsberg 100-m telescope and Arecibo Observatory\\nand testing model predictions. We demonstrate how the new information will provide additional\\ninformation on the solutions of the system geometry.\\n\\\\end{abstract}\\n\\n\\\\vspace{-3ex}\\n\\n\\\\section{Introduction}\\n\\nThe binary pulsar PSR B1913+16 exhibits\\na measurable amount of geodetic precession due to a misalignment of its\\nspin axis and orbital angular momentum (relativistic spin orbit coupling) by an angle $\\\\delta$\\n(see also Stairs et al., for geodetic precession in PSR B1534+12).\\nThe angle between the line of sight and the spin axis, $\\\\zeta$, changes according to:\\n\\\\begin{displaymath}\\n\\\\cos\\\\zeta(t) = -\\\\cos\\\\delta\\\\cos i\\n +\\\\sin\\\\delta\\\\sin i \\\\cos \\\\Omega_{{\\\\rm prec}} (t-T_0) \\\\;,\\n\\\\end{displaymath}\\nwhere $i$ is the orbital inclination of the binary system.\\nGeneral Relativity (GR) predicts a rate of precession $\\\\Omega_{{\\\\rm prec}}=1.21$ deg yr$^{-1}$,\\nleading to a change in the pulse profile and polarization characteristics with time.\\n\\\\\\\\\\nPrevious observations by Weisberg, Romani and Taylor (1989) detected\\na change in the relative amplitude of the trailing and leading component, but no\\nchange in the component separation. Also, there were no\\nchanges in the position angle swing of the linear polarization noted (Cordes, Wasserman \\\\&\\nBlaskiewicz 1990).\\n\\n\\\\section{Recent Observations Cast Some Light}\\n\\nThe evolution of the observed radio pulse profile of PSR B1913+16 would be\\ndetermined when the four parameters\\n$\\\\alpha, \\\\delta, \\\\rho, T_{0}$ were specified for a given $i$, where\\n%\\\\begin{description}\\n$\\\\alpha$ is the angle between the magnetic pole and the spin axis,\\n$\\\\delta$ is as mentioned above,\\n$\\\\rho$ is the angular radius of the emission cone and\\n$T_{0}$ the epoch of precession.\\n%\\\\end{description}\\n\\\\nopagebreak\\nBased on recent data from the Effelsberg 100-m telescope, Kramer (1998) first noticed a\\nchange in the component separation $W$. This allows a solution region in parametric space\\nthat respects GR and the\\n{\\\\bf{\\\\underline{hollow cone model} (HCM)}}.\\n\\\\begin{displaymath}\\n W(t) = 2\\\\arccos\\\\left[\\\\frac{\\\\cos\\\\rho - \\\\cos\\\\alpha \\\\cos\\\\zeta(t)}\\n {\\\\sin\\\\alpha \\\\sin\\\\zeta(t)}\\\\right] \\n\\\\end{displaymath}\\nEffelsberg polarization data has been used\\nin respect with the \\\\underline{\\\\bf rotating vector} \\\\\\\\ \\\\underline{\\\\bf model} {\\\\bf(RVM)},\\nto further narrow down the solution region.\\n\\\\begin{displaymath}\\n \\\\psi(t) = \\\\arctan\\\\left[\\\\frac{\\\\sin\\\\alpha\\\\sin(\\\\phi-\\\\phi_0)}\\n {\\\\cos\\\\alpha \\\\sin\\\\zeta(t) - \\\\sin\\\\alpha\\\\cos\\\\zeta(t)}\\\\right] \\\\quad + const. \\n\\\\end{displaymath}\\n\\nThe inclination of the binary orbit with respect to the line-of-sight, $i$,\\nis known from timing observations modulo the ambiguity\\n$i\\\\longrightarrow 180^\\\\circ - i$. The possibilities are:\\nCase A: $i= 47.2^\\\\circ$, Case B: $i= 132.8^\\\\circ$ \\n\\n\\\\vspace{-2ex}\\n\\n\\\\section{The Solution Today}\\n\\n%\\\\parbox[t]{6cm}{\\n\\\\begin{figure}[h]\\n\\\\centerline{\\n%\\\\hspace*{-1cm}\\n\\\\epsfxsize=7cm\\n\\\\epsfysize=7cm\\n\\\\epsffile{fig.eps}\\n%\\\\caption{The solutions for $\\\\alpha$ and $\\\\delta$ are found in the unshaded regions\\n%within the areas confined by the black curves and the bounding box}\\n\\\\hspace{0.25cm}\\n\\\\parbox[b]{6cm}{\\\\sloppy\\nFigure 1. {\\\\small The pulse component separation data (Effelsberg + Arecibo) in conjunction with the HCM\\nwas used to produce a $\\\\chi^{2}$ area plot indicating the $3\\\\sigma$ confidence level\\nsolutions for $\\\\alpha$ and $\\\\delta$, areas inside the surfaces traced by the black lines.\\nAll possible solutions were then fed into the RVM to produce\\nposition angle curves, which were compared to Effelsberg polarization data,\\nonly allowing for solutions in the unshaded areas. So, the solution must be located on\\na black surface\\ninside an unshaded region (for detailed explanation of this figure check out \\n{\\\\it http://www.mpifr-bonn.mpg.de/staff/akara/psr1913})\\n}}}\\n\\\\end{figure}\\n\\nThe set of plausible solutions has been well limited, as shown in Fig 1.\\nThe inclination of the binary orbit is most likely to be Case B rather than Case A (Wex, Kalogera, Kramer\\n2000). More precise use of the polarization data plus a molding of the\\ntwo models (HCM \\\\& RVM) to specifically suit PSR B1913+16\\n(see also Weisberg \\\\& Taylor in these proceedings)\\ncould further limit the solutions and\\nenable a prediction on the future of this system.\\n\\n\\\\vspace{-2ex}\\n\\n\\\\begin{references}\\n\\\\vspace{-2ex}\\n\\\\reference\\nCordes,~J.M., Wasserman,~I., \\\\& Blaskiewicz,~M. 1990, \\\\apj, 349, 546\\n\\n\\\\reference\\nDamour,~T., \\\\& Ruffini,~R. 1974, Acad. Sci. Paris, 279, s\\\\'erie A, 971\\n\\n\\\\reference\\nDamour,~T., \\\\& Taylor,~J.H. 1992, Phys. Rev. D, 45, 1840\\n\\n\\\\reference\\nHulse,~R.A., \\\\& Taylor,~J.H. 1975, \\\\apj, 195, L51\\n\\n\\\\reference\\nKramer,~M. 1998, \\\\apj, 509, 856\\n\\n\\\\reference\\nTaylor,~J.H. 1999, Proceedings of the XXXIV'th Rencontres de Moriond, to be published\\n\\n\\\\reference\\nWeisberg,~J.M., Romani,~R., \\\\& Taylor,~J.H. 1989, \\\\apj, 347, 1029\\n\\n\\\\reference\\nWex,~N., Kalogera,~V., Kramer,~M. 2000, \\\\apj, 528, 401\\n\\n\\\\end{references}\\n\\n\\\\end{document}\\n\\n\\n\"\n }\n]","isConversational":false},"bibtex":{"kind":"list like","value":[],"string":"[]","isConversational":false}}},{"rowIdx":99,"cells":{"paper_id":{"kind":"string","value":"astro-ph0002100"},"title":{"kind":"string","value":"Reionization of the Universe and the Photoevaporation of Cosmological Minihalos"},"authors":{"kind":"list like","value":[{"author":"Alejandro C. Raga \\affil{Instituto de Astronom\\'{\\i}a, Universidad Nacional Aut\\'onoma de M\\'exico}"}],"string":"[\n {\n \"author\": \"Alejandro C. Raga \\\\affil{Instituto de Astronom\\\\'{\\\\i}a, Universidad Nacional Aut\\\\'onoma de M\\\\'exico}\"\n }\n]","isConversational":false},"abstract":{"kind":"string","value":"The first sources of ionizing radiation to condense out of the dark and neutral IGM sent ionization fronts sweeping outward through their surroundings, overtaking other condensed objects and photoevaporating them. This feedback effect of universal reionization on cosmic structure formation is demonstrated here for the case of a cosmological minihalo of dark matter and baryons exposed to an external source of ionizing radiation with a quasar-like spectrum, just after the passage of the global ionization front created by the source. We model the pre-ionization minihalo as a truncated, nonsingular isothermal sphere in hydrostatic equilibrium following its collapse out of the expanding background universe and virialization. Results are presented of the first gas dynamical simulations of this process, including radiative transfer. A sample of observational diagnostics is also presented, including the spatially-varying ionization levels of C, N, and O in the flow if a trace of heavy elements is present and the integrated column densities of H~I, He~I and II, and C~IV thru the photoevaporating gas at different velocities which would be measured in absorption against a background source like that responsible for the ionization."},"latex":{"kind":"list like","value":[{"name":"shapiro.tex","string":"\\documentclass[proceedings]{rmaa}\n%%\n%% The file `rmaa.cls' should be somewhere in your TeX search path\n%% (e.g, in the current directory, or in a personal or system-wide\n%% directory of LaTeX packages. \n%%\n%% This will not work with old versions of LaTeX: any version\n%% of LaTeX2e should be OK, but LaTeX209 is too old. If LaTeX\n%% complains that it doesn't recognise the command `\\documentclass'\n%% then your LaTeX installation needs updating!\n\n%% The following package allows one to do the citations\n%% semi-automatically. It defines the commands \\cite{KEY},\n%% \\scite{KEY}, and \\pcite{KEY} which respectively produce citations\n%% in the following styles: \n%% (AUTHOR YEAR)\n%% AUTHOR (YEAR)\n%% AUTHOR YEAR\n%% For this to work, you need to pay attention to the formatting of\n%% the `\\bibitem's in your `thebibliography ' environment, qv.\n\\usepackage{rmaacite}\n%% If you would rather do your citations by hand, then comment out the \n%% above line\n\n%% Here, you can put the definitions of your own personal macros.\n%% All the special commands defined in AASTEX 4.0 (e.g. \\ion{}{},\n%% \\gtrsim, \\arcsec, \\apj, etc) are already defined. I haven't checked \n%% if there are any new ones in AASTEX 5.0 yet. \n\\newcommand{\\thOr}{$\\theta^1\\,$C~Ori}\n\\newcommand{\\zero}{_0}\n\\newcommand{\\kms}{\\,\\mbox{km s$^{-1}$}}\n\\newcommand{\\Othree}{[\\ion{O}{3}]~5007\\AA}\n\\renewcommand{\\P}[1]{%\n\\ifnum#1=1\\hbox{OW~168--326E}\\fi\n\\ifnum#1=2\\hbox{OW~167--317}\\fi\n\\ifnum#1=3\\hbox{OW~163--317}\\fi\n\\ifnum#1=5\\hbox{OW~158--323}\\fi\n\\ifnum#1=0\\hbox{OW~171--334}\\fi}\n\n%%\n%% The following commands specify the title, authors etc\n%%\n\\title{Reionization of the Universe and the Photoevaporation of Cosmological\nMinihalos}\n\\author{Paul R. Shapiro \\affil{Department of Astronomy, The University of Texas at Austin, USA} \\and Alejandro C. Raga \\affil{Instituto de Astronom\\'{\\i}a, Universidad Nacional Aut\\'onoma de M\\'exico}}\n%\\author{Paul R. Shapiro \\altaffilmark{1} and Alejandro C. Raga \\altaffilmark{2}}\n%% \\affil{Instituto de Astronom\\'{\\i}a, UNAM, Morelia} }\n%\\altaffiltext{1}{Department of Astronomy, The University of Texas at Austin,\n%Austin, TX 78712 USA}\n%\\altaffiltext{2}{Instituto de Astronom\\'{\\i}a, UNAM, Mexico D.F., Mexico}\n%% Note that the \\affil{} command is inside the argument of the\n%% \\author{} command and that a short version of the address should go \n%% here. More complicated author/address examples are discussed in the \n%% Author Guide (`rmuser.tex') and illustrated in the example document\n%% `rmtest.tex' \n\n%% The full postal addresses are specified here - they will be typeset \n%% at the end of the article. Here is also the place to put email\n%% addresses. \n\\fulladdresses{\n\\item P. R. Shapiro: Department of Astronomy, University of Texas, Austin,\nTX 78712, USA (shapiro@astro.as.utexas.edu)\n\\item A. C. Raga: Instituto de Astronom\\'\\i a,\n UNAM, Apartado Postal 70-264, 04510 M\\'exico D. F.,\nM\\'exico (raga@astroscu.unam.mx)\n}\n%% Note that the `\\fulladdresses' command defines a list-like\n%% environment, so each separate address must be preceded by the\n%% `\\item' command (here there is only one, since the authors share the \n%% same address). \n\n%% Title/author for running headers\n\\shortauthor{Shapiro \\& Raga}\n\\shorttitle{Reionization and photoevaporation}\n%% These will automatically be converted to upper case in the current\n%% style. \n\n%% No more than 5 keywords, chosen from the standard list\n\\keywords{cosmology: theory --- galaxies: formation --- hydrodynamics ---\nintergalactic medium}\n\n%% The abstract:\n\n\\resumen{Las primeras fuentes de radiaci\\'on ionizante que se\n condensaron del IGM generaron frentes de ionizaci\\'on en sus\n alrededores, que iluminaron a otros objetos condensados y los\n fotoevaporaron. Mostramos la retroalimentaci\\'on causada por la\n reionizaci\\'on del Universo en la formaci\\'on de estructuras\n c\\'osmicas para el caso de un mini halo de materia oscura y bariones,\n ionizado por una fuente externa con un espectro similar al de los\n cu\\'asares, justo despu\\'es del paso del frente de ionizaci\\'on\n generado por la fuente. El mini halo es modelado, siguiendo su\n condensaci\\'on del gas en expansi\\'on as\\'{\\i} como su\n virializaci\\'on, como una esfera isot\\'ermica en equilibrio\n hidrost\\'atico. Se presentan los resultados de la primera simulaci\\'on\n hidrodin\\'amica del proceso incluyendo transferencia radiativa.\n Tambi\\'en se dan ejemplos de diagn\\'osticos observacionales,\n incluyendo la distribuci\\'on espacial del grado de ionizaci\\'on en\n el flujo de C, N y O si existen trazas de estos elementos en la\n densidad columnar integrada de H~I, He~I y II, as\\'{\\i} como el C~IV\n a diferentes velocidades en el gas fotoevaporado, que podr\\'{\\i}a\n ser observado en absorci\\'on en contra de la fuente de\n ionizaci\\'on.}\n\n\\abstract{ \nThe first sources of ionizing radiation to condense out of the dark and\nneutral IGM sent ionization fronts sweeping outward through their\nsurroundings, overtaking other condensed objects and photoevaporating them.\nThis feedback effect of universal reionization on cosmic structure \nformation is demonstrated here for the case of a cosmological minihalo of\ndark matter and baryons exposed to an external source of ionizing radiation\nwith a quasar-like spectrum, just after the passage of the global \nionization front created by the source. We model the pre-ionization\nminihalo as a truncated, nonsingular isothermal sphere in hydrostatic\nequilibrium following its collapse out of the expanding background universe\nand virialization. Results are presented of the first gas dynamical\nsimulations of this process,\nincluding radiative transfer. A sample of observational diagnostics is\nalso presented, including the spatially-varying ionization levels\nof C, N, and O in the flow if a trace of heavy elements is present and the \nintegrated column densities of H~I, He~I and II, and C~IV thru the \nphotoevaporating gas at different velocities which would be measured in\nabsorption against a background source like that responsible for the\nionization. }\n%% If your spanish is up to it, you may want to supply the resumen by\n%% uncommenting the following line:\n%\\resumen{Versi\\'on espa\\~nol del ``abstract''}\n%% Alternatively, you can leave the translation to the editors. \n\n\n%% This command is so LaTeX won't stop on errors. I've put it in so\n%% you will still be able to compile the file even if you have lost\n%% the associated PS files of the figures. \n\\nonstopmode\n\n%% The following command is necessary before beginning the text of\n%% your article. There should be a matching \\end{document} at the end\n%% of the file. \n\\begin{document}\n\n%% This command is necessary to typeset the title, abstract, etc. \n\\maketitle\n\n%%\n%% And here starts the text....\n%%\n\\section{Introduction}\n\\label{sec:intro}\nObservations of quasar absorption spectra indicate that the universe\nwas reionized prior to redshift $z=5$. Recent detections of H Lyman alpha\nemission lines from sources at even higher redshift ($z\\leq5.6$) strengthen\nthis conclusion \\cite{Hu98,Wey98}. As new discoveries push the observable\n horizon back in time ever-closer to the epoch of reionization at redshift \n$z>5$, increased awareness of its importance as a missing link in the \ntheory of galaxy formation has caused a great renewal of interest in\nuniversal reionization. If reionization took place early enough, then\nThompson scattering of cosmic microwave background (CMB) photons by free\nelectrons in an ionized intergalactic medium (IGM) would \nalso have left a detectable imprint on\nthe CMB observed today. Recent data on the first Doppler peak in\nthe angular spectrum of CMB anisotropy set limits which imply a \nreionization redshift $z\\lesssim40$ (model-dependent) \\cite{Gri98}.\n(For a review and references on reionization work prior to 1996,\nthe reader is referred to Shapiro 1995, while more recent developments are\nsummarized in Haiman \\& Knox 1999.)\n\nA review of the theory of reionization is outside the scope of this\nbrief report. In keeping with the focus of this meeting, I will\nconfine myself to a description of some recent progress on the\ncalculational side of the problem. To solve the full reionization\nproblem we must also solve the problem of how density fluctuations\nled to galaxy formation and this, in turn, led to secondary energy\nrelease in the form of ionizing and dissociating radiation by the\nstars and quasars formed inside early galaxies, as well as other forms of \nenergy release like supernova explosions, jets and winds, which in turn \ninfluenced the future course of galaxy formation. The modern context for\nthis description is the Cold Dark Matter (CDM) model, in which\na cold, pressure-free,\ncollisionless gas of dark matter dominates the\nmatter density and structure arises from the gravitational amplification of\na scale-free power-spectrum of\ninitially small-amplitude, Gaussian-random-noise primordial density\nfluctuations, in a hierarchical fashion, with small mass objects collapsing\nout first and merging together to form larger-mass objects which\nform later. The calculation of these effects poses an enormous multi-scale \ncomputational challenge, involving numerical gas dynamics coupled to \ngravitational N-body dynamics, which raises the bar of cosmological \nsimulation considerably by adding the requirement that radiative transfer\neffects be included, as well. To simplify matters,\nI will henceforth focus on just one of the central challenges of\nreionization theory, the effect of cosmological ionization fronts.\n\n\\section{Ionization Fronts in the IGM} \n\\label{sec:constraints}\n\nThe neutral, opaque IGM\nout of which the first bound objects condensed was dramatically reheated\nand reionized at some time between a redshift $z\\approx50$ and $z\\approx5$\nby the radiation released by some of these objects.\nAn early analysis of the inhomogeneous nature of reionization for the case\nof short-lived quasars occurring at random positions in a uniform\nIGM was described by Arons \\& Wingert (1972). In that treatment it was\nassumed that each quasar was instantaneously surrounded by an isolated \nH~II region, a ``relict H~II region'' undergoing recombination only, each\nsuch region filling\na volume containing just as many initially neutral H atoms as there were\nionizing photons emitted by the QSO during its lifetime. The effect\nof successive generations of QSO's was accounted for on a \nstatistically-averaged basis by allowing new generations of QSO's to turn \non at random positions, including those inside pre-existing relict H~II\nregions before their H atoms had fully recombined, leading eventually to \nthe complete overlap of these discrete ionized zones.\n\nWhen the first sources\nturned on, they actually\nionized their surroundings, not instantaneously, but\nrather by propagating weak, R-type\nionization fronts which moved outward supersonically with respect to both\nthe neutral gas ahead of and the ionized gas behind the front, racing ahead\nof the hydrodynamical response of the IGM, as first described by \nShapiro (1986) and Shapiro \\& Giroux (1987). These authors solved the\nproblem of the time-varying radius of a spherical I-front which surrounds \nisolated sources in a cosmologically-expanding IGM analytically, taking\nproper account of the I-front jump condition generalized to cosmological\nconditions. They applied these solutions to determine when the I-fronts\nsurrounding isolated sources would grow to overlap and, thereby,\ncomplete the reionization of the universe\n(Donahue \\& Shull 1987 and Meiksen \\& Madau 1993\nsubsequently adopted a similar approach to answer that question).\nThe effect of density inhomogeneity on the rate of I-front propagation\nwas described by a mean ``clumping factor'' $c_l>1$, which\nslowed the I-fronts by increasing the average recombination rate per H atom\ninside clumps. This suffices to describe the rate of I-front propagation\nas long as the\nclumps are either not self-shielding or, if so, only\nabsorb a fraction of the ionizing photons emitted by the central source. \nNumerical radiative transfer methods are currently under\ndevelopment to solve this problem in 3D for the inhomogeneous density \ndistribution which arises as cosmic structure forms, so far limited to a \nfixed density field without gas dynamics (e.g.\\ Abel, Norman, \\& Madau 1999;\nRazoumov \\& Scott 1999). The question of what\ndynamical effect the I-front had on the density inhomogeneity it\nencountered, however, requires further analysis. \n\n\nThe answer depends on the size and density of the clumps overtaken by\nthe I-front. The fate of linear density fluctuations depends upon\ntheir Jeans number, $L_J\\equiv\\lambda/\\lambda_J$, the wavelength in\nunits of the baryon Jeans length in the IGM at temperatures of order\n$10^4\\rm K$. Fluctuations with $L_J<1$ find their growth halted and\nreversed (cf.\\ Shapiro, Giroux, \\& Babul 1994). For nonlinear density\nfluctuations, however, the answer is more complicated, depending upon\nat least three dimensionless parameters, their internal Jeans number,\n$L_J\\equiv R_c/\\lambda_J$, the ratio of the cloud radius $R_c$ to the\nJeans length $\\lambda_J$ inside the cloud at about $10^4{\\rm K}$,\ntheir ``Str\\\"omgren number'' $L_s\\equiv 2 R_c/\\ell_s$, the ratio of\nthe cloud diameter $2R_c$ to the Str\\\"omgren length $\\ell_s$ inside\nthe cloud (the length of a column of gas within which the unshielded\narrival rate of ionizing photons just balances the total recombination\nrate), and their optical depth to H ionizing photons at 13.6 eV,\n$\\tau_{\\rm H}$, before ionization. If $\\tau_{\\rm H}<1$, the I-front\nsweeps across the cloud, leaving an ionized gas at higher pressure\nthan its surroundings, and exits before any mass motion occurs in\nresponse, causing the cloud to blow apart. If $\\tau_{\\rm H}>1$ and\n$L_s>1$, however, the cloud shields itself against ionizing photons,\ntrapping the I-front which enters the cloud, causing it to decelerate\ninside the cloud to the sound speed of the ionized gas before it can\nexit the other side, thereby transforming itself into a weak, D-type\nfront preceded by a shock. Typically, the side facing the source\nexpels a supersonic wind backwards towards the source, which shocks\nthe IGM outside the cloud, while the remaining neutral cloud material\nis accelerated away from the source by the so-called ``rocket effect''\nas the cloud photoevaporates (cf.\\ Spitzer 1978). As long as $L_J<1$\n(the case for gas bound to dark halos with virial velocity less than\n$\\rm 10\\,km\\,s^{-1}$), this photoevaporation proceeds unimpeded by\ngravity. For halos with higher virial velocity, however, $L_J>1$, and\ngravity competes with pressure forces. For a uniform gas of H density\n$n_{\\rm H,c}$, located a distance $r_{\\rm Mpc}$ (in Mpc) from a UV\nsource emitting $N_{\\rm ph,56}$ ionizing photons (in units of\n$\\rm10^{56}s^{-1}$), the Str\\\"omgren length is only\n$\\ell_s\\cong(100\\,{\\rm pc}) (N_{\\rm ph,56}/r_{\\rm Mpc}^2)(n_{\\rm\n H,c}/0.1\\,\\rm cm^{-3})^{-2}$. We focus in what follows on the\nself-shielded case which traps the I-front.\n \n\\section{The Photoevaporation of Dwarf Galaxy Minihalos\nOvertaken by a Cosmological Ionization Front}\n\\label{sec:anal}\n\n\n\n\n\nThe importance of this photoevaporation process has long been\nrecognized in the study of interstellar clouds exposed to ionizing\nstarlight (e.g. Oort \\& Spitzer 1955;\nSpitzer 1978; Bertoldi 1989; Bertoldi \\& McKee 1990;\nLefloch \\& Lazareff 1994; Lizano et al.\\ 1996). Radiation-hydrodynamical \nsimulations were performed in 2D in the early 1980's of\na stellar I-front overtaking a clump inside a molecular\ncloud (Sandford, Whitaker, \\& Klein 1982; Klein, Sandford, \\& Whitaker 1983).\nMore recently, 2D simulations for the case of circumstellar clouds\nionized by a single nearby star have also been performed\n(Mellema et al.\\ 1998). In the cosmological context, however,\nthe importance of this process has only recently been fully appreciated. \nIn proposing the expanding minihalo model to explain Lyman alpha\nforest (``LF'') quasar absorption lines, Bond, Szalay, \\& Silk (1988)\ndiscussed how gas originally confined by the gravity of dark\nminihalos in the CDM model would be expelled by pressure forces\nif photoionization by ionizing background radiation suddently\nheated all the gas to an isothermal condition at $T\\approx10^4\\rm K$.\nThe first radiation-hydrodynamical \nsimulations of the photoevaporation of a primordial density\ninhomogeneity overtaken by a cosmological I-front, however,\nwere described in Shapiro, Raga, \\& Mellema (1997, 1998).\nBarkana \\& Loeb (1999) subsequently considered the relative\nimportance of this process for dwarf galaxy minihalos of different masses\nin the CDM model, using static models of uniformly-illuminated spherical\nclouds in thermal and ionization equilibrium, taking H atom self-shielding\ninto account, and assuming that gas which is heated above the minihalo\nvirial temperature must be evaporated. They concluded that 50\\%--90\\% of \nthe gas in gravitationally bound objects when reionization\noccurred should have been evaporated.\n\\begin{figure}[h]\n\\parbox{0.5\\textwidth}{\n \\includegraphics[height=6.8cm]{shapiro_fig1.ps}}\n \\label{fig1}\n\\begin{minipage}{0.45\\textwidth}\n \\caption{MINIHALO INITIAL CONDITIONS BEFORE REIONIZATION:\nTruncated, nonsingular isothermal sphere (TIS) of gas and dark matter in\nhydrostatic equilibrium (Shapiro, Iliev, \\& Raga 1999) surrounded by the\ncorresponding self-similar spherical infall for an Einstein-de Sitter\nbackground universe (cf.\\ Bertschinger 1985). (a) (Top) gas density and (b)\n(Bottom) gas velocity versus distance from minihalo center.}\n\\end{minipage}\n\\end{figure}\n\n\n\\begin{figure}[t]\n \\parbox{0.5\\textwidth}{%\n \\includegraphics[height=7cm]{shapiro_fig2.ps}}\n \\label{fig2}\n\\begin{minipage}{0.45\\textwidth}\n \\caption{IONIZATION FRONT PHOTOEVAPORATES MINIHALO:\n(a) (Top) I-front position along $x$-axis versus time; (b) (Bottom) Mass\nfraction of the initial mass $M_{\\rm I}$ of minihalo hydrostatic \n core which remains neutral (H~I) versus time. }\n\\end{minipage}\n\\end{figure}\n\n\\begin{figure}[h]\n \\begin{center}\n \\leavevmode\n \\includegraphics[width=\\textwidth]{shapiro_fig3.ps}\n \\caption{PHOTOEVAPORATING MINIHALO.\n50 Myr after turn-on of quasar 1 Mpc to the left of computational box along\nthe $x$-axis. \n(a) (Upper Panel) isocontours of atomic density, logarithmically spaced, \nin $(r,x)-$plane of cylindrical coordinates; (b) (Lower Panel)\nvelocity arrows are plotted with length proportional to gas velocity.\nAn arrow of length equal to the spacing between arrows has velocity\n$30 \\kms$. Solid line shows current extent of gas originally in\nhydrostatic core. Dashed line is I-front (50\\% H-ionization contour).}\n \\label{fig3}\n \\end{center}\n\\end{figure}\n\n\\begin{figure}[p]\n \\begin{center}\n \\leavevmode\n \\includegraphics[height=0.7\\textheight]{shapiro_fig4.ps}\n \\caption{\n PHOTOEVAPORATING MINIHALO. One time-slice 50 Myr after turn-on\n of quasar located 1 Mpc away from cloud to the left of\n computational box along the $x$-axis. From top to bottom: (a)\n isocontours of pressure, logarithmically spaced, in\n $(r,x)-$plane of cylindrical coordinates; (b) pressure along the\n $r=0$ symmetry axis; (c) temperature; (d) H~I fraction; (e) He~I\n (solid) and He~II (dashed) fractions; (f) bound-free optical\n depth along $r=0$ axis at the threshold ionization energies for\n H~I (solid), He~I (dashed), He~II (dotted). Key features of the\n flow are indicated by the numbers which label them on the\n temperature plot: 1 = IGM shock; 2 = contact discontinuity\n between shocked cloud wind and swept up IGM; 3 = wind shock;\n between 3 and 4 = supersonic wind; 4 = I-front; 5 = boundary of\n gas originally in hydrostatic core; 6 = shock in shadow region\n caused by compression of shadow gas by shock-heated gas outside\n shadow.}\n \\label{fig4}\n \\end{center}\n\\end{figure}\n\n\\begin{figure}\n%\\parbox{0.55\\textwidth}\n\\begin{center}\n\\leavevmode\n{\\includegraphics[height=9.0cm]{shapiro_fig5.ps}}%\n%\\begin{minipage}{0.45\\textwidth}\n \\caption{OBSERVATIONAL DIAGNOSTICS OF PHOTOEVAPORATING\n MINIHALO I: IONIZATION STRUCTURE OF METALS.\n Carbon, nitrogen, and oxygen ionic fractions along symmetry\n axis at $t = 50\\rm\\,Myr$.}\n \\label{fig5}\n\\end{center}\n%\\end{minipage}\n% \\begin{center}\n% \\leavevmode\n% \\includegraphics[totalheight=4in]{shapiro_fig5.ps}\n% \\caption{OBSERVATIONAL DIAGNOSTICS OF PHOTOEVAPORATING\n% MINIHALO I: IONIZATION STRUCTURE OF METALS.\n% Carbon, nitrogen, and oxygen ionic fractions along symmetry\n% axis at $t = 50\\rm\\,Myr$.}\n% \\label{fig5}\n% \\end{center}\n\\end{figure}\n\nAs a first study of these important effects, \nShapiro, Raga, \\& Mellema (1997, 1998) simulated the\nphotoevaporation of a uniform, spherical, neutral, intergalactic cloud of \ngas mass $1.5\\times10^6M_\\odot$, radius $R_c=0.5\\,\\rm kpc$, \ndensity $n_{\\rm H,c}=0.1\\,{\\rm cm^{-3}}$ and $T=100\\,\\rm K$, located \n$1\\,\\rm Mpc$ from a quasar with emission spectrum $F_\\nu\\propto\\nu^{-1.8}$\n($\\nu>\\nu_{\\rm H}$) and $N_{\\rm ph}=10^{56}{\\rm s}^{-1}$, initially\nin pressure balance with\nan ambient IGM of density $0.001\\,\\rm cm^{-3}$ which\nat time $t=0$ had\njust been photoionized by the passage of\nthe intergalactic R-type I-front generated when the quasar turned on\n[i.e. $(L_J,L_s,\\tau_H)\\approx (0.1,10,10^3)$].\n [A standard top-hat \nperturbation which collapses and virializes at $z_{\\rm coll}=9$,\nfor example, with total mass $\\cong10^7M_\\odot$, has circular velocity\n$v_c\\cong7\\,\\rm km\\,s^{-1}$, $R_c\\cong560\\rm\\,pc$, and\n$n_{\\rm H,c}=0.1\\,\\rm cm^{-3}$, if $\\Omega_{\\rm bary}h^2=0.03$ and $h=0.5$.]\nThe cloud contained H, He, and heavy elements at $10^{-3}$\ntimes the solar abundance. Our simulations in 2D, axisymmetry used an\nEulerian hydro code with Adaptive Mesh Refinement and\nthe Van~Leer flux-splitting algorithm, which\nsolved nonequilibrium ionization rate equations (for H, He, C, N, O, Ne,\nand S) and included an explicit treatment of radiative transfer\nby taking into account the bound-free opacity of H and He \n(Raga et al.\\ 1995; Mellema et al.\\ 1997; Raga, Mellema, \\& Lundquist 1997).\nThe reader is referred to Shapiro et al.\\ (1997, 1998) for further details.\n\\begin{figure}\n%\\parbox{0.6\\textwidth}\n\\begin{center}\n\\leavevmode\n{\\includegraphics[height=8cm]{shapiro_fig6.ps}}%\n%\\begin{minipage}{0.4\\textwidth}\n \\caption{OBSERVATIONAL DIAGNOSTICS OF PHOTOEVAPORATING\n MINIHALO II. ABSORPTION LINES: \n Cloud column densities ($\\rm cm^{-2}$) along symmetry axis at\n different velocities. (Top) H~I; (Middle) He~I (solid) and\n He~II (dotted); (Bottom) C~IV. Each box labelled with time \n (in Myrs) since QSO turn-on.}\n \\label{fig6}\n%\\end{minipage}\n\\end{center}\n\\end{figure}\n\nHere we shall present for the first time the results of simulations\nof a more realistic, cosmological minihalo, in which the uniform cloud \ndescribed above is replaced by a self-gravitating,\ncentrally condensed object.\nOur initial condition before ionization, shown in Figure 1, is\nthat of a $10^7M_\\odot$ minihalo in an Einstein-de~Sitter\nuniverse ($\\Omega_{\\rm CDM}=1-\\Omega_{\\rm bary}$; $\\Omega_{\\rm\nbary}h^2=0.02$;\n$h=0.7$) which collapses out and virializes at $z_{\\rm coll}=9$,\nyielding a truncated, nonsingular isothermal sphere of radius \n$R_c=0.5\\,\\rm kpc$ in hydrostatic equilibrium\nwith virial temperature $T_{\\rm vir}=5900\\,\\rm K$\nand dark matter velocity dispersion $\\sigma=6.3\\,\\rm km\\,s^{-1}$,\naccording to the solution of Shapiro, Iliev, \\& Raga (1999),\nfor which the finite central density inside a radius about 1/30 of the\ntotal size of the sphere \nis 514 times the surface density. This\nhydrostatic core of radius $R_c$ is embedded in a self-similar,\nspherical, cosmological infall according to Bertschinger (1985).\nThe results of our simulation on an $(r,x)$-grid with $256\\times512$ cells\n(fully refined)\nare summarized in Figures~2--6.\nThe background IGM and infalling gas outside the minihalo are quickly\nionized, and the resulting pressure gradient in the infall region\nconverts the infall into an outflow.\nThe I-front is trapped, however, inside the hydrostatic core\nof the minihalo. Figure~2(a) shows the position of the I-front inside\nthe minihalo as it slows from weak, R-type to weak D-type as it advances\nacross the original hydrostatic core. Figure~2(b) shows the mass of the\nneutral zone within the original hydrostatic core shrinking as\nthe minihalo photoevaporates within about 70~Myrs. \nThis photoevaporation time is significantly less than that found previously for a similar-mass object with\nthe same external source in the uniform cloud case.\nFigures~3 and 4\nshow the structure of the photoevaporative flow 50~Myrs after the\nglobal I-front first overtakes the minihalo, with key features of\nthe flow indicated by the labels on the temperature plot in Figure~4.\nFigure~5 shows the spatial variation of the relative ionic abundances of\nC, N, O ions along the symmetry axis after 50~Myrs.\nAs in the case of the uniform cloud,\nFigure~5 shows the presence at 50~Myrs\nof low as well as high\nionization stages of the metals.\nCompared to the uniform cloud case at the same time-slice, however,\nFigure~5 shows a somewhat higher degree of ionization on the\nside facing the source than in those previous results.\nThe column densities of H~I, He~I and II, and C~IV for minihalo gas of\ndifferent velocities as seen along the symmetry axis at different times\nare shown in Figure~6. \nAt early times, the cloud gas resembles a weak\nDamped Lyman Alpha (``DLA'') absorber with small velocity width \n($\\sim10\\rm\\,km\\,s^{-1}$) and $N_{\\rm H\\,I}\\sim10^{20}\\rm cm^{-2}$,\nwith a \nLF-like red wing ($\\hbox{velocity width}\\,\\sim10\\,\\rm km\\,s^{-1}$)\nwith $N_{\\rm H\\,I}\\sim10^{16}\\rm cm^{-2}$ on the side moving toward\nthe quasar, with a C~IV feature with\n$N_{\\rm C\\,IV}\\sim10^{12}\\rm cm^{-2}$ displaced in\nthis same asymmetric way from the velocity of peak H~I column\ndensity. After 160~Myr,\nhowever, only a narrow H~I feature with LF-like column density\n$N_{\\rm H\\,I}\\sim10^{14}\\rm cm^{-2}$ remains, with \n$N_{\\rm He\\,II}/N_{\\rm H\\,I}\\sim10^2$ and\n$N_{\\rm C\\,IV}/N_{\\rm H\\,I}\\sim\\rm[C]/[C]_\\odot$. \nA comparison with the\nresults of the uniform cloud case in Shapiro et al.\\ (1997, 1998)\nshows that, despite their differences,\nthere is a surprising degree of similarity between the qualitative \nfeatures presented there and those found here for a highly \ncentrally-concentrated minihalo. Future work will extend this study to \nminihalos\nof higher virial temperatures, for which gravity competes more effectively\nwith photoevaporation.\n\n\n\\acknowledgements \nThis work was supported by NASA Grants NAG5-2785, NAG5-7363, and\nNAG5-7821, and NSF Grant ASC-9504046,\nand was made possible by a UT Dean's Fellowship and a National\nChair of Excellence, UNAM, M\\'exico awarded by CONACyT in 1997 to Shapiro.\nThis material is based in part upon work supported by the\nTexas Advanced Research Program under Grant No. 3658-0624-1999.\n\n%% When using the rmaacite package, the \\bibitem command should be of\n%% the format: \n%%\n%% \\bibitem[AUTHOR<YEAR>]{KEY} \n%%\n%% so that the \\cite{KEY}, etc. commands will work properly. \n%% \n%% If you are doing the citations manually, then you can just use\n%% `\\bibitem{}' instead. This will give you a warning about\n%% `multiply-defined labels' which you can safely ignore.\n%% \n\\enlargethispage{4ex}\n\\begin{thebibliography}\n\n%\\bibitem[Bally et al.{}<1995>]{p:Bal95} \n% Bally, J., Devine, D. \\& Sutherland, R. 1995, In: S. Lizano \\&\n% J.~M. Torrelles (eds.): {Circumstellar Disks, Outflows and Star\n% Formation}, RMAA (Serie de Conferencias) {1}, 19\n\n\\bibitem[{}<>]{}\nAbel, T., Norman, M. L., \\& Madau, P. 1999, ApJ, {523}, 66\n\n\\bibitem[{Arons} \\& {Wingert}<1972>]{Aro72}\n{Arons}, J., \\& {Wingert}, D.~W. 1972, ApJ, {177}, 1\n\n\\bibitem[{}<>]{} Barkana, R., \\& Loeb, A. 1999, ApJ, {523}, 54\n\n\\bibitem[{}<>]{} \nBertoldi, F. 1989, ApJ, {346}, 735\n\n\\bibitem[{}<>]{} \nBertoldi, F., \\& McKee, C. 1990, ApJ, {354}, 529\n\n\\bibitem[{}<>]{}\nBertschinger, E. 1985, ApJS, {58}, 39\n\n\\bibitem[{}<>]{} \nBond, J. R., Szalay, A. S., \\& Silk, J. 1988, \nApJ, 324, 627\n\n\\bibitem[{}<>]{}\nDonahue, M., \\& Shull, J. M. 1987, ApJ, {323}, L13\n\n\\bibitem[{Griffiths}, {Barbosa}, \\& {Liddle}<1998>]{Gri98}\n{Griffiths}, L.~M., {Barbosa}, D., \\& {Liddle}, A.~R. 1998,\nMNRAS, {308}, 854\n\n\\bibitem[{Haiman} \\& {Knox}<1999>]{Hai99}\n{Haiman}, Z., \\& {Knox}, L. 1999, in ASP Conf.\\ Ser.\\ Vol.\\ 181, Sloan Summit on Microwave Foreground, ed.\\ A.~de~Oliveira \\& M. Tegmark (San Francisco: Astronomical Society of the Pacific), 227 (astro-ph/9902311)\n\n\\bibitem[{Hu}, {Cowie}, \\& {McMahon}<1998>]{Hu98}\n {Hu}, E.~M., {Cowie}, L.~L., \\& {McMahon}, R.~G. 1998, ApJ, {502}, 99\n\n\\bibitem[{}<>]{} \nKlein, R. I., Sandford, M. T., \\& Whitaker, R. W. 1983, \nApJ, {271}, L69\n\n\\bibitem[{}<>]{}\nLefloch, B., \\& Lazareff, B. 1994, \nA\\&A, {289}, 559\n\n\\bibitem[{}<>]{} \nLizano, S., Cant\\'o, J., Garay, G., \\& Hollenbach, D. 1996, \nApJ, {468}, 739\n\n\\bibitem[{}<>]{}\nMeiksen, A., \\& Madau, P. 1993,\nApJ, {412}, 34\n\n\\bibitem[{}<>]{} \nMellema, G., Raga, A. C., Canto, J., Lundqvist, P., Balick, B.,\n Steffen, W., \\& Noriega-Crespo, A. 1998, \nA\\&A, {331}, 335\n\n\\bibitem[{}<>]{}\n Oort, J. H., \\& Spitzer, L. 1955, ApJ, {121}, 6\n\n\\bibitem[{}<>]{} \nRaga, A. C., Taylor, S. D., Cabrit, S., \\& Biro, S. 1995, \n A.Ap., {296}, 833\n\n\\bibitem[{}<>]{} \nRaga, A. C., Mellema, G., \\& Lundquist, P. 1997, ApJS, {109}, 517\n\n\\bibitem[{}<>]{}\nRazoumov, A., \\& Scott, D. 1999, MNRAS, {309}, 287 \n\n\\bibitem[{}<>]{}\nSandford, M. T., Whitaker, R. W., \\& Klein, R. I. 1982, ApJ, {260}, 183\n\n\\bibitem[{Shapiro}<1995>]{Sha95}\n{Shapiro}, P.~R. 1995, in ASP Conf.\\ Ser.\\ Vol.\\ 80, The Physics of the Interstellar Medium and\nThe Intergalactic Medium, ed. A.~Ferrara, C.~F.~McKee,\nC.~Heiles, \\& P.~R.~Shapiro (San Francisco: Astronomical Society of the Pacific), 55\n \n\\bibitem[{}<>]{} \nShapiro, P. R. 1986, PASP, {98}, 1014\n\n\\bibitem[{}<>]{} \nShapiro, P. R., \\& Giroux, M. L. 1987, ApJ, {321}, L107\n\n\\bibitem[{}<>]{}\n Shapiro, P. R., Giroux, M. L., \\& Babul, A. 1994, ApJ, {427}, 25\n\n\\bibitem[{}<>]{}\nShapiro, P. R., Iliev, I. T., \\& Raga, A. C. 1999, MNRAS, {307}, 203\n\n\\bibitem[{}<>]{}\nShapiro, P. R., Raga, A. C., \\& Mellema, G. 1997, in {Structure and Evolution of the Intergalactic Medium From QSO \n Absorption Line Systems}, ed. P.~Petitjean \\& S.~Charlot (Gif-sur-Yvette: Editions Fronti\\'eres), 41\n\n\\bibitem[{}<>]{}\nShapiro, P. R., Raga, A. C., \\& Mellema, G. 1998, \nin Mem.\\ Soc.\\ Astron.\\ Italiana\\ Vol.\\ 69, {H$_2$ in the Early Universe}, ed. E.~Corbelli, D.~Galli, \\& F.~Palla, 463 (astro-ph/9804117)\n\n\\bibitem[{}<>]{} \nSpitzer, L. 1978, {Physical Processes in the Interstellar Medium} (New York: Wiley Interscience)\n\n\\bibitem[{Weymann} et al.{}<1998>]{Wey98}\n {Weymann}, R.~J., {Stern}, D., {Bunker}, A., {Spinrad}, H.,\n{Chaffee}, F.~H., {Thompson}, R.~I., \\& {Storrie-Lombardi}, L.~J. 1998\n ApJ, {505}, L95\n\n\\end{thebibliography}\n\n\\end{document}\n\n\n"}],"string":"[\n {\n \"name\": \"shapiro.tex\",\n \"string\": \"\\\\documentclass[proceedings]{rmaa}\\n%%\\n%% The file `rmaa.cls' should be somewhere in your TeX search path\\n%% (e.g, in the current directory, or in a personal or system-wide\\n%% directory of LaTeX packages. \\n%%\\n%% This will not work with old versions of LaTeX: any version\\n%% of LaTeX2e should be OK, but LaTeX209 is too old. If LaTeX\\n%% complains that it doesn't recognise the command `\\\\documentclass'\\n%% then your LaTeX installation needs updating!\\n\\n%% The following package allows one to do the citations\\n%% semi-automatically. It defines the commands \\\\cite{KEY},\\n%% \\\\scite{KEY}, and \\\\pcite{KEY} which respectively produce citations\\n%% in the following styles: \\n%% (AUTHOR YEAR)\\n%% AUTHOR (YEAR)\\n%% AUTHOR YEAR\\n%% For this to work, you need to pay attention to the formatting of\\n%% the `\\\\bibitem's in your `thebibliography ' environment, qv.\\n\\\\usepackage{rmaacite}\\n%% If you would rather do your citations by hand, then comment out the \\n%% above line\\n\\n%% Here, you can put the definitions of your own personal macros.\\n%% All the special commands defined in AASTEX 4.0 (e.g. \\\\ion{}{},\\n%% \\\\gtrsim, \\\\arcsec, \\\\apj, etc) are already defined. I haven't checked \\n%% if there are any new ones in AASTEX 5.0 yet. \\n\\\\newcommand{\\\\thOr}{$\\\\theta^1\\\\,$C~Ori}\\n\\\\newcommand{\\\\zero}{_0}\\n\\\\newcommand{\\\\kms}{\\\\,\\\\mbox{km s$^{-1}$}}\\n\\\\newcommand{\\\\Othree}{[\\\\ion{O}{3}]~5007\\\\AA}\\n\\\\renewcommand{\\\\P}[1]{%\\n\\\\ifnum#1=1\\\\hbox{OW~168--326E}\\\\fi\\n\\\\ifnum#1=2\\\\hbox{OW~167--317}\\\\fi\\n\\\\ifnum#1=3\\\\hbox{OW~163--317}\\\\fi\\n\\\\ifnum#1=5\\\\hbox{OW~158--323}\\\\fi\\n\\\\ifnum#1=0\\\\hbox{OW~171--334}\\\\fi}\\n\\n%%\\n%% The following commands specify the title, authors etc\\n%%\\n\\\\title{Reionization of the Universe and the Photoevaporation of Cosmological\\nMinihalos}\\n\\\\author{Paul R. Shapiro \\\\affil{Department of Astronomy, The University of Texas at Austin, USA} \\\\and Alejandro C. Raga \\\\affil{Instituto de Astronom\\\\'{\\\\i}a, Universidad Nacional Aut\\\\'onoma de M\\\\'exico}}\\n%\\\\author{Paul R. Shapiro \\\\altaffilmark{1} and Alejandro C. Raga \\\\altaffilmark{2}}\\n%% \\\\affil{Instituto de Astronom\\\\'{\\\\i}a, UNAM, Morelia} }\\n%\\\\altaffiltext{1}{Department of Astronomy, The University of Texas at Austin,\\n%Austin, TX 78712 USA}\\n%\\\\altaffiltext{2}{Instituto de Astronom\\\\'{\\\\i}a, UNAM, Mexico D.F., Mexico}\\n%% Note that the \\\\affil{} command is inside the argument of the\\n%% \\\\author{} command and that a short version of the address should go \\n%% here. More complicated author/address examples are discussed in the \\n%% Author Guide (`rmuser.tex') and illustrated in the example document\\n%% `rmtest.tex' \\n\\n%% The full postal addresses are specified here - they will be typeset \\n%% at the end of the article. Here is also the place to put email\\n%% addresses. \\n\\\\fulladdresses{\\n\\\\item P. R. Shapiro: Department of Astronomy, University of Texas, Austin,\\nTX 78712, USA (shapiro@astro.as.utexas.edu)\\n\\\\item A. C. Raga: Instituto de Astronom\\\\'\\\\i a,\\n UNAM, Apartado Postal 70-264, 04510 M\\\\'exico D. F.,\\nM\\\\'exico (raga@astroscu.unam.mx)\\n}\\n%% Note that the `\\\\fulladdresses' command defines a list-like\\n%% environment, so each separate address must be preceded by the\\n%% `\\\\item' command (here there is only one, since the authors share the \\n%% same address). \\n\\n%% Title/author for running headers\\n\\\\shortauthor{Shapiro \\\\& Raga}\\n\\\\shorttitle{Reionization and photoevaporation}\\n%% These will automatically be converted to upper case in the current\\n%% style. \\n\\n%% No more than 5 keywords, chosen from the standard list\\n\\\\keywords{cosmology: theory --- galaxies: formation --- hydrodynamics ---\\nintergalactic medium}\\n\\n%% The abstract:\\n\\n\\\\resumen{Las primeras fuentes de radiaci\\\\'on ionizante que se\\n condensaron del IGM generaron frentes de ionizaci\\\\'on en sus\\n alrededores, que iluminaron a otros objetos condensados y los\\n fotoevaporaron. Mostramos la retroalimentaci\\\\'on causada por la\\n reionizaci\\\\'on del Universo en la formaci\\\\'on de estructuras\\n c\\\\'osmicas para el caso de un mini halo de materia oscura y bariones,\\n ionizado por una fuente externa con un espectro similar al de los\\n cu\\\\'asares, justo despu\\\\'es del paso del frente de ionizaci\\\\'on\\n generado por la fuente. El mini halo es modelado, siguiendo su\\n condensaci\\\\'on del gas en expansi\\\\'on as\\\\'{\\\\i} como su\\n virializaci\\\\'on, como una esfera isot\\\\'ermica en equilibrio\\n hidrost\\\\'atico. Se presentan los resultados de la primera simulaci\\\\'on\\n hidrodin\\\\'amica del proceso incluyendo transferencia radiativa.\\n Tambi\\\\'en se dan ejemplos de diagn\\\\'osticos observacionales,\\n incluyendo la distribuci\\\\'on espacial del grado de ionizaci\\\\'on en\\n el flujo de C, N y O si existen trazas de estos elementos en la\\n densidad columnar integrada de H~I, He~I y II, as\\\\'{\\\\i} como el C~IV\\n a diferentes velocidades en el gas fotoevaporado, que podr\\\\'{\\\\i}a\\n ser observado en absorci\\\\'on en contra de la fuente de\\n ionizaci\\\\'on.}\\n\\n\\\\abstract{ \\nThe first sources of ionizing radiation to condense out of the dark and\\nneutral IGM sent ionization fronts sweeping outward through their\\nsurroundings, overtaking other condensed objects and photoevaporating them.\\nThis feedback effect of universal reionization on cosmic structure \\nformation is demonstrated here for the case of a cosmological minihalo of\\ndark matter and baryons exposed to an external source of ionizing radiation\\nwith a quasar-like spectrum, just after the passage of the global \\nionization front created by the source. We model the pre-ionization\\nminihalo as a truncated, nonsingular isothermal sphere in hydrostatic\\nequilibrium following its collapse out of the expanding background universe\\nand virialization. Results are presented of the first gas dynamical\\nsimulations of this process,\\nincluding radiative transfer. A sample of observational diagnostics is\\nalso presented, including the spatially-varying ionization levels\\nof C, N, and O in the flow if a trace of heavy elements is present and the \\nintegrated column densities of H~I, He~I and II, and C~IV thru the \\nphotoevaporating gas at different velocities which would be measured in\\nabsorption against a background source like that responsible for the\\nionization. }\\n%% If your spanish is up to it, you may want to supply the resumen by\\n%% uncommenting the following line:\\n%\\\\resumen{Versi\\\\'on espa\\\\~nol del ``abstract''}\\n%% Alternatively, you can leave the translation to the editors. \\n\\n\\n%% This command is so LaTeX won't stop on errors. I've put it in so\\n%% you will still be able to compile the file even if you have lost\\n%% the associated PS files of the figures. \\n\\\\nonstopmode\\n\\n%% The following command is necessary before beginning the text of\\n%% your article. There should be a matching \\\\end{document} at the end\\n%% of the file. \\n\\\\begin{document}\\n\\n%% This command is necessary to typeset the title, abstract, etc. \\n\\\\maketitle\\n\\n%%\\n%% And here starts the text....\\n%%\\n\\\\section{Introduction}\\n\\\\label{sec:intro}\\nObservations of quasar absorption spectra indicate that the universe\\nwas reionized prior to redshift $z=5$. Recent detections of H Lyman alpha\\nemission lines from sources at even higher redshift ($z\\\\leq5.6$) strengthen\\nthis conclusion \\\\cite{Hu98,Wey98}. As new discoveries push the observable\\n horizon back in time ever-closer to the epoch of reionization at redshift \\n$z>5$, increased awareness of its importance as a missing link in the \\ntheory of galaxy formation has caused a great renewal of interest in\\nuniversal reionization. If reionization took place early enough, then\\nThompson scattering of cosmic microwave background (CMB) photons by free\\nelectrons in an ionized intergalactic medium (IGM) would \\nalso have left a detectable imprint on\\nthe CMB observed today. Recent data on the first Doppler peak in\\nthe angular spectrum of CMB anisotropy set limits which imply a \\nreionization redshift $z\\\\lesssim40$ (model-dependent) \\\\cite{Gri98}.\\n(For a review and references on reionization work prior to 1996,\\nthe reader is referred to Shapiro 1995, while more recent developments are\\nsummarized in Haiman \\\\& Knox 1999.)\\n\\nA review of the theory of reionization is outside the scope of this\\nbrief report. In keeping with the focus of this meeting, I will\\nconfine myself to a description of some recent progress on the\\ncalculational side of the problem. To solve the full reionization\\nproblem we must also solve the problem of how density fluctuations\\nled to galaxy formation and this, in turn, led to secondary energy\\nrelease in the form of ionizing and dissociating radiation by the\\nstars and quasars formed inside early galaxies, as well as other forms of \\nenergy release like supernova explosions, jets and winds, which in turn \\ninfluenced the future course of galaxy formation. The modern context for\\nthis description is the Cold Dark Matter (CDM) model, in which\\na cold, pressure-free,\\ncollisionless gas of dark matter dominates the\\nmatter density and structure arises from the gravitational amplification of\\na scale-free power-spectrum of\\ninitially small-amplitude, Gaussian-random-noise primordial density\\nfluctuations, in a hierarchical fashion, with small mass objects collapsing\\nout first and merging together to form larger-mass objects which\\nform later. The calculation of these effects poses an enormous multi-scale \\ncomputational challenge, involving numerical gas dynamics coupled to \\ngravitational N-body dynamics, which raises the bar of cosmological \\nsimulation considerably by adding the requirement that radiative transfer\\neffects be included, as well. To simplify matters,\\nI will henceforth focus on just one of the central challenges of\\nreionization theory, the effect of cosmological ionization fronts.\\n\\n\\\\section{Ionization Fronts in the IGM} \\n\\\\label{sec:constraints}\\n\\nThe neutral, opaque IGM\\nout of which the first bound objects condensed was dramatically reheated\\nand reionized at some time between a redshift $z\\\\approx50$ and $z\\\\approx5$\\nby the radiation released by some of these objects.\\nAn early analysis of the inhomogeneous nature of reionization for the case\\nof short-lived quasars occurring at random positions in a uniform\\nIGM was described by Arons \\\\& Wingert (1972). In that treatment it was\\nassumed that each quasar was instantaneously surrounded by an isolated \\nH~II region, a ``relict H~II region'' undergoing recombination only, each\\nsuch region filling\\na volume containing just as many initially neutral H atoms as there were\\nionizing photons emitted by the QSO during its lifetime. The effect\\nof successive generations of QSO's was accounted for on a \\nstatistically-averaged basis by allowing new generations of QSO's to turn \\non at random positions, including those inside pre-existing relict H~II\\nregions before their H atoms had fully recombined, leading eventually to \\nthe complete overlap of these discrete ionized zones.\\n\\nWhen the first sources\\nturned on, they actually\\nionized their surroundings, not instantaneously, but\\nrather by propagating weak, R-type\\nionization fronts which moved outward supersonically with respect to both\\nthe neutral gas ahead of and the ionized gas behind the front, racing ahead\\nof the hydrodynamical response of the IGM, as first described by \\nShapiro (1986) and Shapiro \\\\& Giroux (1987). These authors solved the\\nproblem of the time-varying radius of a spherical I-front which surrounds \\nisolated sources in a cosmologically-expanding IGM analytically, taking\\nproper account of the I-front jump condition generalized to cosmological\\nconditions. They applied these solutions to determine when the I-fronts\\nsurrounding isolated sources would grow to overlap and, thereby,\\ncomplete the reionization of the universe\\n(Donahue \\\\& Shull 1987 and Meiksen \\\\& Madau 1993\\nsubsequently adopted a similar approach to answer that question).\\nThe effect of density inhomogeneity on the rate of I-front propagation\\nwas described by a mean ``clumping factor'' $c_l>1$, which\\nslowed the I-fronts by increasing the average recombination rate per H atom\\ninside clumps. This suffices to describe the rate of I-front propagation\\nas long as the\\nclumps are either not self-shielding or, if so, only\\nabsorb a fraction of the ionizing photons emitted by the central source. \\nNumerical radiative transfer methods are currently under\\ndevelopment to solve this problem in 3D for the inhomogeneous density \\ndistribution which arises as cosmic structure forms, so far limited to a \\nfixed density field without gas dynamics (e.g.\\\\ Abel, Norman, \\\\& Madau 1999;\\nRazoumov \\\\& Scott 1999). The question of what\\ndynamical effect the I-front had on the density inhomogeneity it\\nencountered, however, requires further analysis. \\n\\n\\nThe answer depends on the size and density of the clumps overtaken by\\nthe I-front. The fate of linear density fluctuations depends upon\\ntheir Jeans number, $L_J\\\\equiv\\\\lambda/\\\\lambda_J$, the wavelength in\\nunits of the baryon Jeans length in the IGM at temperatures of order\\n$10^4\\\\rm K$. Fluctuations with $L_J<1$ find their growth halted and\\nreversed (cf.\\\\ Shapiro, Giroux, \\\\& Babul 1994). For nonlinear density\\nfluctuations, however, the answer is more complicated, depending upon\\nat least three dimensionless parameters, their internal Jeans number,\\n$L_J\\\\equiv R_c/\\\\lambda_J$, the ratio of the cloud radius $R_c$ to the\\nJeans length $\\\\lambda_J$ inside the cloud at about $10^4{\\\\rm K}$,\\ntheir ``Str\\\\\\\"omgren number'' $L_s\\\\equiv 2 R_c/\\\\ell_s$, the ratio of\\nthe cloud diameter $2R_c$ to the Str\\\\\\\"omgren length $\\\\ell_s$ inside\\nthe cloud (the length of a column of gas within which the unshielded\\narrival rate of ionizing photons just balances the total recombination\\nrate), and their optical depth to H ionizing photons at 13.6 eV,\\n$\\\\tau_{\\\\rm H}$, before ionization. If $\\\\tau_{\\\\rm H}<1$, the I-front\\nsweeps across the cloud, leaving an ionized gas at higher pressure\\nthan its surroundings, and exits before any mass motion occurs in\\nresponse, causing the cloud to blow apart. If $\\\\tau_{\\\\rm H}>1$ and\\n$L_s>1$, however, the cloud shields itself against ionizing photons,\\ntrapping the I-front which enters the cloud, causing it to decelerate\\ninside the cloud to the sound speed of the ionized gas before it can\\nexit the other side, thereby transforming itself into a weak, D-type\\nfront preceded by a shock. Typically, the side facing the source\\nexpels a supersonic wind backwards towards the source, which shocks\\nthe IGM outside the cloud, while the remaining neutral cloud material\\nis accelerated away from the source by the so-called ``rocket effect''\\nas the cloud photoevaporates (cf.\\\\ Spitzer 1978). As long as $L_J<1$\\n(the case for gas bound to dark halos with virial velocity less than\\n$\\\\rm 10\\\\,km\\\\,s^{-1}$), this photoevaporation proceeds unimpeded by\\ngravity. For halos with higher virial velocity, however, $L_J>1$, and\\ngravity competes with pressure forces. For a uniform gas of H density\\n$n_{\\\\rm H,c}$, located a distance $r_{\\\\rm Mpc}$ (in Mpc) from a UV\\nsource emitting $N_{\\\\rm ph,56}$ ionizing photons (in units of\\n$\\\\rm10^{56}s^{-1}$), the Str\\\\\\\"omgren length is only\\n$\\\\ell_s\\\\cong(100\\\\,{\\\\rm pc}) (N_{\\\\rm ph,56}/r_{\\\\rm Mpc}^2)(n_{\\\\rm\\n H,c}/0.1\\\\,\\\\rm cm^{-3})^{-2}$. We focus in what follows on the\\nself-shielded case which traps the I-front.\\n \\n\\\\section{The Photoevaporation of Dwarf Galaxy Minihalos\\nOvertaken by a Cosmological Ionization Front}\\n\\\\label{sec:anal}\\n\\n\\n\\n\\n\\nThe importance of this photoevaporation process has long been\\nrecognized in the study of interstellar clouds exposed to ionizing\\nstarlight (e.g. Oort \\\\& Spitzer 1955;\\nSpitzer 1978; Bertoldi 1989; Bertoldi \\\\& McKee 1990;\\nLefloch \\\\& Lazareff 1994; Lizano et al.\\\\ 1996). Radiation-hydrodynamical \\nsimulations were performed in 2D in the early 1980's of\\na stellar I-front overtaking a clump inside a molecular\\ncloud (Sandford, Whitaker, \\\\& Klein 1982; Klein, Sandford, \\\\& Whitaker 1983).\\nMore recently, 2D simulations for the case of circumstellar clouds\\nionized by a single nearby star have also been performed\\n(Mellema et al.\\\\ 1998). In the cosmological context, however,\\nthe importance of this process has only recently been fully appreciated. \\nIn proposing the expanding minihalo model to explain Lyman alpha\\nforest (``LF'') quasar absorption lines, Bond, Szalay, \\\\& Silk (1988)\\ndiscussed how gas originally confined by the gravity of dark\\nminihalos in the CDM model would be expelled by pressure forces\\nif photoionization by ionizing background radiation suddently\\nheated all the gas to an isothermal condition at $T\\\\approx10^4\\\\rm K$.\\nThe first radiation-hydrodynamical \\nsimulations of the photoevaporation of a primordial density\\ninhomogeneity overtaken by a cosmological I-front, however,\\nwere described in Shapiro, Raga, \\\\& Mellema (1997, 1998).\\nBarkana \\\\& Loeb (1999) subsequently considered the relative\\nimportance of this process for dwarf galaxy minihalos of different masses\\nin the CDM model, using static models of uniformly-illuminated spherical\\nclouds in thermal and ionization equilibrium, taking H atom self-shielding\\ninto account, and assuming that gas which is heated above the minihalo\\nvirial temperature must be evaporated. They concluded that 50\\\\%--90\\\\% of \\nthe gas in gravitationally bound objects when reionization\\noccurred should have been evaporated.\\n\\\\begin{figure}[h]\\n\\\\parbox{0.5\\\\textwidth}{\\n \\\\includegraphics[height=6.8cm]{shapiro_fig1.ps}}\\n \\\\label{fig1}\\n\\\\begin{minipage}{0.45\\\\textwidth}\\n \\\\caption{MINIHALO INITIAL CONDITIONS BEFORE REIONIZATION:\\nTruncated, nonsingular isothermal sphere (TIS) of gas and dark matter in\\nhydrostatic equilibrium (Shapiro, Iliev, \\\\& Raga 1999) surrounded by the\\ncorresponding self-similar spherical infall for an Einstein-de Sitter\\nbackground universe (cf.\\\\ Bertschinger 1985). (a) (Top) gas density and (b)\\n(Bottom) gas velocity versus distance from minihalo center.}\\n\\\\end{minipage}\\n\\\\end{figure}\\n\\n\\n\\\\begin{figure}[t]\\n \\\\parbox{0.5\\\\textwidth}{%\\n \\\\includegraphics[height=7cm]{shapiro_fig2.ps}}\\n \\\\label{fig2}\\n\\\\begin{minipage}{0.45\\\\textwidth}\\n \\\\caption{IONIZATION FRONT PHOTOEVAPORATES MINIHALO:\\n(a) (Top) I-front position along $x$-axis versus time; (b) (Bottom) Mass\\nfraction of the initial mass $M_{\\\\rm I}$ of minihalo hydrostatic \\n core which remains neutral (H~I) versus time. }\\n\\\\end{minipage}\\n\\\\end{figure}\\n\\n\\\\begin{figure}[h]\\n \\\\begin{center}\\n \\\\leavevmode\\n \\\\includegraphics[width=\\\\textwidth]{shapiro_fig3.ps}\\n \\\\caption{PHOTOEVAPORATING MINIHALO.\\n50 Myr after turn-on of quasar 1 Mpc to the left of computational box along\\nthe $x$-axis. \\n(a) (Upper Panel) isocontours of atomic density, logarithmically spaced, \\nin $(r,x)-$plane of cylindrical coordinates; (b) (Lower Panel)\\nvelocity arrows are plotted with length proportional to gas velocity.\\nAn arrow of length equal to the spacing between arrows has velocity\\n$30 \\\\kms$. Solid line shows current extent of gas originally in\\nhydrostatic core. Dashed line is I-front (50\\\\% H-ionization contour).}\\n \\\\label{fig3}\\n \\\\end{center}\\n\\\\end{figure}\\n\\n\\\\begin{figure}[p]\\n \\\\begin{center}\\n \\\\leavevmode\\n \\\\includegraphics[height=0.7\\\\textheight]{shapiro_fig4.ps}\\n \\\\caption{\\n PHOTOEVAPORATING MINIHALO. One time-slice 50 Myr after turn-on\\n of quasar located 1 Mpc away from cloud to the left of\\n computational box along the $x$-axis. From top to bottom: (a)\\n isocontours of pressure, logarithmically spaced, in\\n $(r,x)-$plane of cylindrical coordinates; (b) pressure along the\\n $r=0$ symmetry axis; (c) temperature; (d) H~I fraction; (e) He~I\\n (solid) and He~II (dashed) fractions; (f) bound-free optical\\n depth along $r=0$ axis at the threshold ionization energies for\\n H~I (solid), He~I (dashed), He~II (dotted). Key features of the\\n flow are indicated by the numbers which label them on the\\n temperature plot: 1 = IGM shock; 2 = contact discontinuity\\n between shocked cloud wind and swept up IGM; 3 = wind shock;\\n between 3 and 4 = supersonic wind; 4 = I-front; 5 = boundary of\\n gas originally in hydrostatic core; 6 = shock in shadow region\\n caused by compression of shadow gas by shock-heated gas outside\\n shadow.}\\n \\\\label{fig4}\\n \\\\end{center}\\n\\\\end{figure}\\n\\n\\\\begin{figure}\\n%\\\\parbox{0.55\\\\textwidth}\\n\\\\begin{center}\\n\\\\leavevmode\\n{\\\\includegraphics[height=9.0cm]{shapiro_fig5.ps}}%\\n%\\\\begin{minipage}{0.45\\\\textwidth}\\n \\\\caption{OBSERVATIONAL DIAGNOSTICS OF PHOTOEVAPORATING\\n MINIHALO I: IONIZATION STRUCTURE OF METALS.\\n Carbon, nitrogen, and oxygen ionic fractions along symmetry\\n axis at $t = 50\\\\rm\\\\,Myr$.}\\n \\\\label{fig5}\\n\\\\end{center}\\n%\\\\end{minipage}\\n% \\\\begin{center}\\n% \\\\leavevmode\\n% \\\\includegraphics[totalheight=4in]{shapiro_fig5.ps}\\n% \\\\caption{OBSERVATIONAL DIAGNOSTICS OF PHOTOEVAPORATING\\n% MINIHALO I: IONIZATION STRUCTURE OF METALS.\\n% Carbon, nitrogen, and oxygen ionic fractions along symmetry\\n% axis at $t = 50\\\\rm\\\\,Myr$.}\\n% \\\\label{fig5}\\n% \\\\end{center}\\n\\\\end{figure}\\n\\nAs a first study of these important effects, \\nShapiro, Raga, \\\\& Mellema (1997, 1998) simulated the\\nphotoevaporation of a uniform, spherical, neutral, intergalactic cloud of \\ngas mass $1.5\\\\times10^6M_\\\\odot$, radius $R_c=0.5\\\\,\\\\rm kpc$, \\ndensity $n_{\\\\rm H,c}=0.1\\\\,{\\\\rm cm^{-3}}$ and $T=100\\\\,\\\\rm K$, located \\n$1\\\\,\\\\rm Mpc$ from a quasar with emission spectrum $F_\\\\nu\\\\propto\\\\nu^{-1.8}$\\n($\\\\nu>\\\\nu_{\\\\rm H}$) and $N_{\\\\rm ph}=10^{56}{\\\\rm s}^{-1}$, initially\\nin pressure balance with\\nan ambient IGM of density $0.001\\\\,\\\\rm cm^{-3}$ which\\nat time $t=0$ had\\njust been photoionized by the passage of\\nthe intergalactic R-type I-front generated when the quasar turned on\\n[i.e. $(L_J,L_s,\\\\tau_H)\\\\approx (0.1,10,10^3)$].\\n [A standard top-hat \\nperturbation which collapses and virializes at $z_{\\\\rm coll}=9$,\\nfor example, with total mass $\\\\cong10^7M_\\\\odot$, has circular velocity\\n$v_c\\\\cong7\\\\,\\\\rm km\\\\,s^{-1}$, $R_c\\\\cong560\\\\rm\\\\,pc$, and\\n$n_{\\\\rm H,c}=0.1\\\\,\\\\rm cm^{-3}$, if $\\\\Omega_{\\\\rm bary}h^2=0.03$ and $h=0.5$.]\\nThe cloud contained H, He, and heavy elements at $10^{-3}$\\ntimes the solar abundance. Our simulations in 2D, axisymmetry used an\\nEulerian hydro code with Adaptive Mesh Refinement and\\nthe Van~Leer flux-splitting algorithm, which\\nsolved nonequilibrium ionization rate equations (for H, He, C, N, O, Ne,\\nand S) and included an explicit treatment of radiative transfer\\nby taking into account the bound-free opacity of H and He \\n(Raga et al.\\\\ 1995; Mellema et al.\\\\ 1997; Raga, Mellema, \\\\& Lundquist 1997).\\nThe reader is referred to Shapiro et al.\\\\ (1997, 1998) for further details.\\n\\\\begin{figure}\\n%\\\\parbox{0.6\\\\textwidth}\\n\\\\begin{center}\\n\\\\leavevmode\\n{\\\\includegraphics[height=8cm]{shapiro_fig6.ps}}%\\n%\\\\begin{minipage}{0.4\\\\textwidth}\\n \\\\caption{OBSERVATIONAL DIAGNOSTICS OF PHOTOEVAPORATING\\n MINIHALO II. ABSORPTION LINES: \\n Cloud column densities ($\\\\rm cm^{-2}$) along symmetry axis at\\n different velocities. (Top) H~I; (Middle) He~I (solid) and\\n He~II (dotted); (Bottom) C~IV. Each box labelled with time \\n (in Myrs) since QSO turn-on.}\\n \\\\label{fig6}\\n%\\\\end{minipage}\\n\\\\end{center}\\n\\\\end{figure}\\n\\nHere we shall present for the first time the results of simulations\\nof a more realistic, cosmological minihalo, in which the uniform cloud \\ndescribed above is replaced by a self-gravitating,\\ncentrally condensed object.\\nOur initial condition before ionization, shown in Figure 1, is\\nthat of a $10^7M_\\\\odot$ minihalo in an Einstein-de~Sitter\\nuniverse ($\\\\Omega_{\\\\rm CDM}=1-\\\\Omega_{\\\\rm bary}$; $\\\\Omega_{\\\\rm\\nbary}h^2=0.02$;\\n$h=0.7$) which collapses out and virializes at $z_{\\\\rm coll}=9$,\\nyielding a truncated, nonsingular isothermal sphere of radius \\n$R_c=0.5\\\\,\\\\rm kpc$ in hydrostatic equilibrium\\nwith virial temperature $T_{\\\\rm vir}=5900\\\\,\\\\rm K$\\nand dark matter velocity dispersion $\\\\sigma=6.3\\\\,\\\\rm km\\\\,s^{-1}$,\\naccording to the solution of Shapiro, Iliev, \\\\& Raga (1999),\\nfor which the finite central density inside a radius about 1/30 of the\\ntotal size of the sphere \\nis 514 times the surface density. This\\nhydrostatic core of radius $R_c$ is embedded in a self-similar,\\nspherical, cosmological infall according to Bertschinger (1985).\\nThe results of our simulation on an $(r,x)$-grid with $256\\\\times512$ cells\\n(fully refined)\\nare summarized in Figures~2--6.\\nThe background IGM and infalling gas outside the minihalo are quickly\\nionized, and the resulting pressure gradient in the infall region\\nconverts the infall into an outflow.\\nThe I-front is trapped, however, inside the hydrostatic core\\nof the minihalo. Figure~2(a) shows the position of the I-front inside\\nthe minihalo as it slows from weak, R-type to weak D-type as it advances\\nacross the original hydrostatic core. Figure~2(b) shows the mass of the\\nneutral zone within the original hydrostatic core shrinking as\\nthe minihalo photoevaporates within about 70~Myrs. \\nThis photoevaporation time is significantly less than that found previously for a similar-mass object with\\nthe same external source in the uniform cloud case.\\nFigures~3 and 4\\nshow the structure of the photoevaporative flow 50~Myrs after the\\nglobal I-front first overtakes the minihalo, with key features of\\nthe flow indicated by the labels on the temperature plot in Figure~4.\\nFigure~5 shows the spatial variation of the relative ionic abundances of\\nC, N, O ions along the symmetry axis after 50~Myrs.\\nAs in the case of the uniform cloud,\\nFigure~5 shows the presence at 50~Myrs\\nof low as well as high\\nionization stages of the metals.\\nCompared to the uniform cloud case at the same time-slice, however,\\nFigure~5 shows a somewhat higher degree of ionization on the\\nside facing the source than in those previous results.\\nThe column densities of H~I, He~I and II, and C~IV for minihalo gas of\\ndifferent velocities as seen along the symmetry axis at different times\\nare shown in Figure~6. \\nAt early times, the cloud gas resembles a weak\\nDamped Lyman Alpha (``DLA'') absorber with small velocity width \\n($\\\\sim10\\\\rm\\\\,km\\\\,s^{-1}$) and $N_{\\\\rm H\\\\,I}\\\\sim10^{20}\\\\rm cm^{-2}$,\\nwith a \\nLF-like red wing ($\\\\hbox{velocity width}\\\\,\\\\sim10\\\\,\\\\rm km\\\\,s^{-1}$)\\nwith $N_{\\\\rm H\\\\,I}\\\\sim10^{16}\\\\rm cm^{-2}$ on the side moving toward\\nthe quasar, with a C~IV feature with\\n$N_{\\\\rm C\\\\,IV}\\\\sim10^{12}\\\\rm cm^{-2}$ displaced in\\nthis same asymmetric way from the velocity of peak H~I column\\ndensity. After 160~Myr,\\nhowever, only a narrow H~I feature with LF-like column density\\n$N_{\\\\rm H\\\\,I}\\\\sim10^{14}\\\\rm cm^{-2}$ remains, with \\n$N_{\\\\rm He\\\\,II}/N_{\\\\rm H\\\\,I}\\\\sim10^2$ and\\n$N_{\\\\rm C\\\\,IV}/N_{\\\\rm H\\\\,I}\\\\sim\\\\rm[C]/[C]_\\\\odot$. \\nA comparison with the\\nresults of the uniform cloud case in Shapiro et al.\\\\ (1997, 1998)\\nshows that, despite their differences,\\nthere is a surprising degree of similarity between the qualitative \\nfeatures presented there and those found here for a highly \\ncentrally-concentrated minihalo. Future work will extend this study to \\nminihalos\\nof higher virial temperatures, for which gravity competes more effectively\\nwith photoevaporation.\\n\\n\\n\\\\acknowledgements \\nThis work was supported by NASA Grants NAG5-2785, NAG5-7363, and\\nNAG5-7821, and NSF Grant ASC-9504046,\\nand was made possible by a UT Dean's Fellowship and a National\\nChair of Excellence, UNAM, M\\\\'exico awarded by CONACyT in 1997 to Shapiro.\\nThis material is based in part upon work supported by the\\nTexas Advanced Research Program under Grant No. 3658-0624-1999.\\n\\n%% When using the rmaacite package, the \\\\bibitem command should be of\\n%% the format: \\n%%\\n%% \\\\bibitem[AUTHOR<YEAR>]{KEY} \\n%%\\n%% so that the \\\\cite{KEY}, etc. commands will work properly. \\n%% \\n%% If you are doing the citations manually, then you can just use\\n%% `\\\\bibitem{}' instead. This will give you a warning about\\n%% `multiply-defined labels' which you can safely ignore.\\n%% \\n\\\\enlargethispage{4ex}\\n\\\\begin{thebibliography}\\n\\n%\\\\bibitem[Bally et al.{}<1995>]{p:Bal95} \\n% Bally, J., Devine, D. \\\\& Sutherland, R. 1995, In: S. Lizano \\\\&\\n% J.~M. Torrelles (eds.): {Circumstellar Disks, Outflows and Star\\n% Formation}, RMAA (Serie de Conferencias) {1}, 19\\n\\n\\\\bibitem[{}<>]{}\\nAbel, T., Norman, M. L., \\\\& Madau, P. 1999, ApJ, {523}, 66\\n\\n\\\\bibitem[{Arons} \\\\& {Wingert}<1972>]{Aro72}\\n{Arons}, J., \\\\& {Wingert}, D.~W. 1972, ApJ, {177}, 1\\n\\n\\\\bibitem[{}<>]{} Barkana, R., \\\\& Loeb, A. 1999, ApJ, {523}, 54\\n\\n\\\\bibitem[{}<>]{} \\nBertoldi, F. 1989, ApJ, {346}, 735\\n\\n\\\\bibitem[{}<>]{} \\nBertoldi, F., \\\\& McKee, C. 1990, ApJ, {354}, 529\\n\\n\\\\bibitem[{}<>]{}\\nBertschinger, E. 1985, ApJS, {58}, 39\\n\\n\\\\bibitem[{}<>]{} \\nBond, J. R., Szalay, A. S., \\\\& Silk, J. 1988, \\nApJ, 324, 627\\n\\n\\\\bibitem[{}<>]{}\\nDonahue, M., \\\\& Shull, J. M. 1987, ApJ, {323}, L13\\n\\n\\\\bibitem[{Griffiths}, {Barbosa}, \\\\& {Liddle}<1998>]{Gri98}\\n{Griffiths}, L.~M., {Barbosa}, D., \\\\& {Liddle}, A.~R. 1998,\\nMNRAS, {308}, 854\\n\\n\\\\bibitem[{Haiman} \\\\& {Knox}<1999>]{Hai99}\\n{Haiman}, Z., \\\\& {Knox}, L. 1999, in ASP Conf.\\\\ Ser.\\\\ Vol.\\\\ 181, Sloan Summit on Microwave Foreground, ed.\\\\ A.~de~Oliveira \\\\& M. Tegmark (San Francisco: Astronomical Society of the Pacific), 227 (astro-ph/9902311)\\n\\n\\\\bibitem[{Hu}, {Cowie}, \\\\& {McMahon}<1998>]{Hu98}\\n {Hu}, E.~M., {Cowie}, L.~L., \\\\& {McMahon}, R.~G. 1998, ApJ, {502}, 99\\n\\n\\\\bibitem[{}<>]{} \\nKlein, R. I., Sandford, M. T., \\\\& Whitaker, R. W. 1983, \\nApJ, {271}, L69\\n\\n\\\\bibitem[{}<>]{}\\nLefloch, B., \\\\& Lazareff, B. 1994, \\nA\\\\&A, {289}, 559\\n\\n\\\\bibitem[{}<>]{} \\nLizano, S., Cant\\\\'o, J., Garay, G., \\\\& Hollenbach, D. 1996, \\nApJ, {468}, 739\\n\\n\\\\bibitem[{}<>]{}\\nMeiksen, A., \\\\& Madau, P. 1993,\\nApJ, {412}, 34\\n\\n\\\\bibitem[{}<>]{} \\nMellema, G., Raga, A. C., Canto, J., Lundqvist, P., Balick, B.,\\n Steffen, W., \\\\& Noriega-Crespo, A. 1998, \\nA\\\\&A, {331}, 335\\n\\n\\\\bibitem[{}<>]{}\\n Oort, J. H., \\\\& Spitzer, L. 1955, ApJ, {121}, 6\\n\\n\\\\bibitem[{}<>]{} \\nRaga, A. C., Taylor, S. D., Cabrit, S., \\\\& Biro, S. 1995, \\n A.Ap., {296}, 833\\n\\n\\\\bibitem[{}<>]{} \\nRaga, A. C., Mellema, G., \\\\& Lundquist, P. 1997, ApJS, {109}, 517\\n\\n\\\\bibitem[{}<>]{}\\nRazoumov, A., \\\\& Scott, D. 1999, MNRAS, {309}, 287 \\n\\n\\\\bibitem[{}<>]{}\\nSandford, M. T., Whitaker, R. W., \\\\& Klein, R. I. 1982, ApJ, {260}, 183\\n\\n\\\\bibitem[{Shapiro}<1995>]{Sha95}\\n{Shapiro}, P.~R. 1995, in ASP Conf.\\\\ Ser.\\\\ Vol.\\\\ 80, The Physics of the Interstellar Medium and\\nThe Intergalactic Medium, ed. A.~Ferrara, C.~F.~McKee,\\nC.~Heiles, \\\\& P.~R.~Shapiro (San Francisco: Astronomical Society of the Pacific), 55\\n \\n\\\\bibitem[{}<>]{} \\nShapiro, P. R. 1986, PASP, {98}, 1014\\n\\n\\\\bibitem[{}<>]{} \\nShapiro, P. R., \\\\& Giroux, M. L. 1987, ApJ, {321}, L107\\n\\n\\\\bibitem[{}<>]{}\\n Shapiro, P. R., Giroux, M. L., \\\\& Babul, A. 1994, ApJ, {427}, 25\\n\\n\\\\bibitem[{}<>]{}\\nShapiro, P. R., Iliev, I. T., \\\\& Raga, A. C. 1999, MNRAS, {307}, 203\\n\\n\\\\bibitem[{}<>]{}\\nShapiro, P. R., Raga, A. C., \\\\& Mellema, G. 1997, in {Structure and Evolution of the Intergalactic Medium From QSO \\n Absorption Line Systems}, ed. P.~Petitjean \\\\& S.~Charlot (Gif-sur-Yvette: Editions Fronti\\\\'eres), 41\\n\\n\\\\bibitem[{}<>]{}\\nShapiro, P. R., Raga, A. C., \\\\& Mellema, G. 1998, \\nin Mem.\\\\ Soc.\\\\ Astron.\\\\ Italiana\\\\ Vol.\\\\ 69, {H$_2$ in the Early Universe}, ed. E.~Corbelli, D.~Galli, \\\\& F.~Palla, 463 (astro-ph/9804117)\\n\\n\\\\bibitem[{}<>]{} \\nSpitzer, L. 1978, {Physical Processes in the Interstellar Medium} (New York: Wiley Interscience)\\n\\n\\\\bibitem[{Weymann} et al.{}<1998>]{Wey98}\\n {Weymann}, R.~J., {Stern}, D., {Bunker}, A., {Spinrad}, H.,\\n{Chaffee}, F.~H., {Thompson}, R.~I., \\\\& {Storrie-Lombardi}, L.~J. 1998\\n ApJ, {505}, L95\\n\\n\\\\end{thebibliography}\\n\\n\\\\end{document}\\n\\n\\n\"\n }\n]","isConversational":false},"bibtex":{"kind":"list like","value":[{"name":"astro-ph0002100.extracted_bib","string":"\\begin{thebibliography}\n\n%\\bibitem[Bally et al.{}<1995>]{p:Bal95} \n% Bally, J., Devine, D. \\& Sutherland, R. 1995, In: S. Lizano \\&\n% J.~M. Torrelles (eds.): {Circumstellar Disks, Outflows and Star\n% Formation}, RMAA (Serie de Conferencias) {1}, 19\n\n\\bibitem[{}<>]{}\nAbel, T., Norman, M. L., \\& Madau, P. 1999, ApJ, {523}, 66\n\n\\bibitem[{Arons} \\& {Wingert}<1972>]{Aro72}\n{Arons}, J., \\& {Wingert}, D.~W. 1972, ApJ, {177}, 1\n\n\\bibitem[{}<>]{} Barkana, R., \\& Loeb, A. 1999, ApJ, {523}, 54\n\n\\bibitem[{}<>]{} \nBertoldi, F. 1989, ApJ, {346}, 735\n\n\\bibitem[{}<>]{} \nBertoldi, F., \\& McKee, C. 1990, ApJ, {354}, 529\n\n\\bibitem[{}<>]{}\nBertschinger, E. 1985, ApJS, {58}, 39\n\n\\bibitem[{}<>]{} \nBond, J. R., Szalay, A. S., \\& Silk, J. 1988, \nApJ, 324, 627\n\n\\bibitem[{}<>]{}\nDonahue, M., \\& Shull, J. M. 1987, ApJ, {323}, L13\n\n\\bibitem[{Griffiths}, {Barbosa}, \\& {Liddle}<1998>]{Gri98}\n{Griffiths}, L.~M., {Barbosa}, D., \\& {Liddle}, A.~R. 1998,\nMNRAS, {308}, 854\n\n\\bibitem[{Haiman} \\& {Knox}<1999>]{Hai99}\n{Haiman}, Z., \\& {Knox}, L. 1999, in ASP Conf.\\ Ser.\\ Vol.\\ 181, Sloan Summit on Microwave Foreground, ed.\\ A.~de~Oliveira \\& M. Tegmark (San Francisco: Astronomical Society of the Pacific), 227 (astro-ph/9902311)\n\n\\bibitem[{Hu}, {Cowie}, \\& {McMahon}<1998>]{Hu98}\n {Hu}, E.~M., {Cowie}, L.~L., \\& {McMahon}, R.~G. 1998, ApJ, {502}, 99\n\n\\bibitem[{}<>]{} \nKlein, R. I., Sandford, M. T., \\& Whitaker, R. W. 1983, \nApJ, {271}, L69\n\n\\bibitem[{}<>]{}\nLefloch, B., \\& Lazareff, B. 1994, \nA\\&A, {289}, 559\n\n\\bibitem[{}<>]{} \nLizano, S., Cant\\'o, J., Garay, G., \\& Hollenbach, D. 1996, \nApJ, {468}, 739\n\n\\bibitem[{}<>]{}\nMeiksen, A., \\& Madau, P. 1993,\nApJ, {412}, 34\n\n\\bibitem[{}<>]{} \nMellema, G., Raga, A. C., Canto, J., Lundqvist, P., Balick, B.,\n Steffen, W., \\& Noriega-Crespo, A. 1998, \nA\\&A, {331}, 335\n\n\\bibitem[{}<>]{}\n Oort, J. H., \\& Spitzer, L. 1955, ApJ, {121}, 6\n\n\\bibitem[{}<>]{} \nRaga, A. C., Taylor, S. D., Cabrit, S., \\& Biro, S. 1995, \n A.Ap., {296}, 833\n\n\\bibitem[{}<>]{} \nRaga, A. C., Mellema, G., \\& Lundquist, P. 1997, ApJS, {109}, 517\n\n\\bibitem[{}<>]{}\nRazoumov, A., \\& Scott, D. 1999, MNRAS, {309}, 287 \n\n\\bibitem[{}<>]{}\nSandford, M. T., Whitaker, R. W., \\& Klein, R. I. 1982, ApJ, {260}, 183\n\n\\bibitem[{Shapiro}<1995>]{Sha95}\n{Shapiro}, P.~R. 1995, in ASP Conf.\\ Ser.\\ Vol.\\ 80, The Physics of the Interstellar Medium and\nThe Intergalactic Medium, ed. A.~Ferrara, C.~F.~McKee,\nC.~Heiles, \\& P.~R.~Shapiro (San Francisco: Astronomical Society of the Pacific), 55\n \n\\bibitem[{}<>]{} \nShapiro, P. R. 1986, PASP, {98}, 1014\n\n\\bibitem[{}<>]{} \nShapiro, P. R., \\& Giroux, M. L. 1987, ApJ, {321}, L107\n\n\\bibitem[{}<>]{}\n Shapiro, P. R., Giroux, M. L., \\& Babul, A. 1994, ApJ, {427}, 25\n\n\\bibitem[{}<>]{}\nShapiro, P. R., Iliev, I. T., \\& Raga, A. C. 1999, MNRAS, {307}, 203\n\n\\bibitem[{}<>]{}\nShapiro, P. R., Raga, A. C., \\& Mellema, G. 1997, in {Structure and Evolution of the Intergalactic Medium From QSO \n Absorption Line Systems}, ed. P.~Petitjean \\& S.~Charlot (Gif-sur-Yvette: Editions Fronti\\'eres), 41\n\n\\bibitem[{}<>]{}\nShapiro, P. R., Raga, A. C., \\& Mellema, G. 1998, \nin Mem.\\ Soc.\\ Astron.\\ Italiana\\ Vol.\\ 69, {H$_2$ in the Early Universe}, ed. E.~Corbelli, D.~Galli, \\& F.~Palla, 463 (astro-ph/9804117)\n\n\\bibitem[{}<>]{} \nSpitzer, L. 1978, {Physical Processes in the Interstellar Medium} (New York: Wiley Interscience)\n\n\\bibitem[{Weymann} et al.{}<1998>]{Wey98}\n {Weymann}, R.~J., {Stern}, D., {Bunker}, A., {Spinrad}, H.,\n{Chaffee}, F.~H., {Thompson}, R.~I., \\& {Storrie-Lombardi}, L.~J. 1998\n ApJ, {505}, L95\n\n\\end{thebibliography}"}],"string":"[\n {\n \"name\": \"astro-ph0002100.extracted_bib\",\n \"string\": \"\\\\begin{thebibliography}\\n\\n%\\\\bibitem[Bally et al.{}<1995>]{p:Bal95} \\n% Bally, J., Devine, D. \\\\& Sutherland, R. 1995, In: S. Lizano \\\\&\\n% J.~M. Torrelles (eds.): {Circumstellar Disks, Outflows and Star\\n% Formation}, RMAA (Serie de Conferencias) {1}, 19\\n\\n\\\\bibitem[{}<>]{}\\nAbel, T., Norman, M. L., \\\\& Madau, P. 1999, ApJ, {523}, 66\\n\\n\\\\bibitem[{Arons} \\\\& {Wingert}<1972>]{Aro72}\\n{Arons}, J., \\\\& {Wingert}, D.~W. 1972, ApJ, {177}, 1\\n\\n\\\\bibitem[{}<>]{} Barkana, R., \\\\& Loeb, A. 1999, ApJ, {523}, 54\\n\\n\\\\bibitem[{}<>]{} \\nBertoldi, F. 1989, ApJ, {346}, 735\\n\\n\\\\bibitem[{}<>]{} \\nBertoldi, F., \\\\& McKee, C. 1990, ApJ, {354}, 529\\n\\n\\\\bibitem[{}<>]{}\\nBertschinger, E. 1985, ApJS, {58}, 39\\n\\n\\\\bibitem[{}<>]{} \\nBond, J. R., Szalay, A. S., \\\\& Silk, J. 1988, \\nApJ, 324, 627\\n\\n\\\\bibitem[{}<>]{}\\nDonahue, M., \\\\& Shull, J. M. 1987, ApJ, {323}, L13\\n\\n\\\\bibitem[{Griffiths}, {Barbosa}, \\\\& {Liddle}<1998>]{Gri98}\\n{Griffiths}, L.~M., {Barbosa}, D., \\\\& {Liddle}, A.~R. 1998,\\nMNRAS, {308}, 854\\n\\n\\\\bibitem[{Haiman} \\\\& {Knox}<1999>]{Hai99}\\n{Haiman}, Z., \\\\& {Knox}, L. 1999, in ASP Conf.\\\\ Ser.\\\\ Vol.\\\\ 181, Sloan Summit on Microwave Foreground, ed.\\\\ A.~de~Oliveira \\\\& M. Tegmark (San Francisco: Astronomical Society of the Pacific), 227 (astro-ph/9902311)\\n\\n\\\\bibitem[{Hu}, {Cowie}, \\\\& {McMahon}<1998>]{Hu98}\\n {Hu}, E.~M., {Cowie}, L.~L., \\\\& {McMahon}, R.~G. 1998, ApJ, {502}, 99\\n\\n\\\\bibitem[{}<>]{} \\nKlein, R. I., Sandford, M. T., \\\\& Whitaker, R. W. 1983, \\nApJ, {271}, L69\\n\\n\\\\bibitem[{}<>]{}\\nLefloch, B., \\\\& Lazareff, B. 1994, \\nA\\\\&A, {289}, 559\\n\\n\\\\bibitem[{}<>]{} \\nLizano, S., Cant\\\\'o, J., Garay, G., \\\\& Hollenbach, D. 1996, \\nApJ, {468}, 739\\n\\n\\\\bibitem[{}<>]{}\\nMeiksen, A., \\\\& Madau, P. 1993,\\nApJ, {412}, 34\\n\\n\\\\bibitem[{}<>]{} \\nMellema, G., Raga, A. C., Canto, J., Lundqvist, P., Balick, B.,\\n Steffen, W., \\\\& Noriega-Crespo, A. 1998, \\nA\\\\&A, {331}, 335\\n\\n\\\\bibitem[{}<>]{}\\n Oort, J. H., \\\\& Spitzer, L. 1955, ApJ, {121}, 6\\n\\n\\\\bibitem[{}<>]{} \\nRaga, A. C., Taylor, S. D., Cabrit, S., \\\\& Biro, S. 1995, \\n A.Ap., {296}, 833\\n\\n\\\\bibitem[{}<>]{} \\nRaga, A. C., Mellema, G., \\\\& Lundquist, P. 1997, ApJS, {109}, 517\\n\\n\\\\bibitem[{}<>]{}\\nRazoumov, A., \\\\& Scott, D. 1999, MNRAS, {309}, 287 \\n\\n\\\\bibitem[{}<>]{}\\nSandford, M. T., Whitaker, R. W., \\\\& Klein, R. I. 1982, ApJ, {260}, 183\\n\\n\\\\bibitem[{Shapiro}<1995>]{Sha95}\\n{Shapiro}, P.~R. 1995, in ASP Conf.\\\\ Ser.\\\\ Vol.\\\\ 80, The Physics of the Interstellar Medium and\\nThe Intergalactic Medium, ed. A.~Ferrara, C.~F.~McKee,\\nC.~Heiles, \\\\& P.~R.~Shapiro (San Francisco: Astronomical Society of the Pacific), 55\\n \\n\\\\bibitem[{}<>]{} \\nShapiro, P. R. 1986, PASP, {98}, 1014\\n\\n\\\\bibitem[{}<>]{} \\nShapiro, P. R., \\\\& Giroux, M. L. 1987, ApJ, {321}, L107\\n\\n\\\\bibitem[{}<>]{}\\n Shapiro, P. R., Giroux, M. L., \\\\& Babul, A. 1994, ApJ, {427}, 25\\n\\n\\\\bibitem[{}<>]{}\\nShapiro, P. R., Iliev, I. T., \\\\& Raga, A. C. 1999, MNRAS, {307}, 203\\n\\n\\\\bibitem[{}<>]{}\\nShapiro, P. R., Raga, A. C., \\\\& Mellema, G. 1997, in {Structure and Evolution of the Intergalactic Medium From QSO \\n Absorption Line Systems}, ed. P.~Petitjean \\\\& S.~Charlot (Gif-sur-Yvette: Editions Fronti\\\\'eres), 41\\n\\n\\\\bibitem[{}<>]{}\\nShapiro, P. R., Raga, A. C., \\\\& Mellema, G. 1998, \\nin Mem.\\\\ Soc.\\\\ Astron.\\\\ Italiana\\\\ Vol.\\\\ 69, {H$_2$ in the Early Universe}, ed. E.~Corbelli, D.~Galli, \\\\& F.~Palla, 463 (astro-ph/9804117)\\n\\n\\\\bibitem[{}<>]{} \\nSpitzer, L. 1978, {Physical Processes in the Interstellar Medium} (New York: Wiley Interscience)\\n\\n\\\\bibitem[{Weymann} et al.{}<1998>]{Wey98}\\n {Weymann}, R.~J., {Stern}, D., {Bunker}, A., {Spinrad}, H.,\\n{Chaffee}, F.~H., {Thompson}, R.~I., \\\\& {Storrie-Lombardi}, L.~J. 1998\\n ApJ, {505}, L95\\n\\n\\\\end{thebibliography}\"\n }\n]","isConversational":false}}}],"truncated":false,"partial":false},"paginationData":{"pageIndex":0,"numItemsPerPage":100,"numTotalItems":1318468,"offset":0,"length":100}},"jwt":"eyJhbGciOiJFZERTQSIsImtpZCI6IjVHZDBvd0g5MTM2eDZjc1FvbE1zcktNWUZoRVFoUm5PVVVybEpjOUhaUEEifQ.eyJyZWFkIjp0cnVlLCJwZXJtaXNzaW9ucyI6eyJyZXBvLmNvbnRlbnQucmVhZCI6dHJ1ZX0sImlhdCI6MTc4ODI0MDk3NywianRpIjoiOGE2YzcwNjctZGU1Ni00MGQ4LTkzMzEtYWI3MjMwOWVmNTQ5Iiwic3ViIjoiL2RhdGFzZXRzL3N5bnRoZXRpeC1pbnN0aXR1dGUvbGF0ZXgtZGF0YS1wdWIiLCJleHAiOjE3ODgyNDQ1NzcsImlzcyI6Imh0dHBzOi8vaHVnZ2luZ2ZhY2UuY28ifQ.hXEt07ybQhftAg5Ekpx0I8AEUkhvbiwCY3NFA--IrmTAH6DDA_kRYgMA3PZTA0_zOlijPfQQuKYELeGA10nfAw","displayUrls":true,"splitSizeSummaries":[{"config":"default","split":"train","numRows":1318468,"numBytesParquet":110673004212}]},"discussionsStats":{"closed":0,"open":1,"total":1},"fullWidth":true,"hasGatedAccess":true,"hasFullAccess":true,"isEmbedded":false,"savedQueries":{"community":[],"user":[]}}">
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astro-ph0002001 | QSO Absorption Line Constraints on Intragroup High--Velocity Clouds | [
{
"author": "Jane~C.~Charlton\\altaffilmark{1}"
},
{
"author": "Christopher~W.~Churchill"
},
{
"author": "and Jane~R.~Rigby"
}
] | We show that the number statistics of moderate redshift {\MgII} and Lyman limit absorbers may rule out the hypothesis that high velocity clouds are infalling intragroup material. | [
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"string": "\\documentstyle[emulateapj,rotate,times]{article}\n%\\documentstyle[11pt,rotate,aaspp4]{article}\n%\\documentstyle[12pt,aasms4]{article}\n \n% this is the modification \n \n%-----------------------------------------------------------------------------\n%\n% perso... | [
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"name": "astro-ph0002001.extracted_bib",
"string": "\\begin{thebibliography}{XXX}\n\n\\bibitem[Bergeron \\& Boiss\\'e 1991]{bb91}\nBergeron, J., \\& Boiss\\'e, P. 1991, A\\&A, 243, 344\n\n\\bibitem[Bergeron \\etal 1992]{bergeron92}\nBergeron, J., Cristiani, S., \\& Shaver, P. A. 1992, A\\&A, 257, 417\n\n\... |
astro-ph0002002 | Point source models for the gravitational lens B1608+656: Indeterminacy in the prediction of the Hubble constant | [
{
"author": "Gabriela Surpi and Roger Blandford"
}
] | We apply elliptical isothermal mass models to reproduce the point source properties, i.e. image positions, flux density ratios and time delay ratios, of the quadruple lens B1608+656. A wide set of suitable solutions is found, showing that models that only fit the properties of point sources are under-constrained and ca... | [
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"name": "gsurpi.tex",
"string": "\\documentstyle[11pt,paspconf,epsf]{article}\n\n\\begin{document}\n\\title{Point source models for the gravitational lens B1608+656:\nIndeterminacy in the prediction of the Hubble constant}\n\n\\author{Gabriela Surpi and Roger Blandford}\n\\affil{California Institute of Te... | [] |
astro-ph0002003 | Compact Stellar Systems in the Fornax Cluster: Super-massive Star Clusters or Extremely Compact Dwarf Galaxies? | [
{
"author": "M. J. Drinkwater$^{1}$"
},
{
"author": "J. B. Jones$^{2}$"
},
{
"author": "M. D. Gregg$^{3}$"
},
{
"author": "S. Phillipps$^{4}$"
}
] | and % | [
{
"name": "fss4.tex",
"string": "%\n% LaTeX template file for\n% Publications of the Astronomical Society of Australia.\n% Version 2.4 - 28 April 1997\n%\n%\\documentstyle[12pt,psfig]{article}\n\\documentstyle[11pt,psfig]{article}\n%\n% Baselineskip may be altered if desired.\n%\n\\baselineskip=2em\n%\n% A ... | [] |
astro-ph0002004 | Extracting Energy from a Black Hole through Its Disk | [
{
"author": "Li-Xin Li"
}
] | When some magnetic field lines connect a Kerr black hole with a disk rotating around it, energy and angular momentum are transferred between them. If the black hole rotates faster than the disk, $ca/GM_H>0.36$ for a thin Keplerian disk, then energy and angular momentum are extracted from the black hole and transferred ... | [
{
"name": "bh_disk.tex",
"string": "% bh_disk.tex for ApJ Letters\n\n\\documentstyle[12pt,aaspp4]{article}\n\\begin{document}\n\n\\title{Extracting Energy from a Black Hole through Its Disk}\n\n\\author{Li-Xin Li}\n\\affil{Princeton University Observatory, Princeton, NJ 08544--1001, USA}\n\\affil{E-mail: lx... | [] |
astro-ph0002005 | A Comparison of Ultraviolet, Optical, and X-Ray Imagery of Selected Fields in the Cygnus Loop | [
{
"author": "\\sc Charles W.\\ Danforth\\altaffilmark{1}"
},
{
"author": "Robert H.\\ Cornett\\altaffilmark{2}"
},
{
"author": "N. A. Levenson\\altaffilmark{1}"
},
{
"author": "William P.\\ Blair\\altaffilmark{1}"
},
{
"author": "Theodore P.\\ Stecher\\altaffilmark{3}"
}
] | During the Astro-1 and Astro-2 Space Shuttle missions in 1990 and 1995, far ultraviolet (FUV) images of five 40\arcmin\ diameter fields around the rim of the Cygnus Loop supernova remnant were observed with the Ultraviolet Imaging Telescope (UIT). These fields sampled a broad range of conditions including both radiativ... | [
{
"name": "psfig.tex",
"string": "% Psfig/TeX Release 1.2\n% dvips version\n%\n% All software, documentation, and related files in this distribution of\n% psfig/tex are Copyright 1987, 1988 Trevor J. Darrell\n%\n% Permission is granted for use and non-profit distribution of psfig/tex \n% providing that this... | [
{
"name": "astro-ph0002005.extracted_bib",
"string": "\\begin{thebibliography}{Danforth00}\n\\bibitem[Arendt, Dwek, \\& Leisawitz 1992]{Arendt92}\nArendt, R.G., Dwek, E., \\& Leisawitz, D. 1992, \\apj, 400, 562\n\\bibitem[Bedogni \\& Woodward (1990)]{Bedogni90}\nBedogni, R. \\& Woodward, P. R. 1990, \\aap, ... |
astro-ph0002006 | ULTRA HIGH ENERGY COSMIC RAYS: the theoretical challenge | [
{
"author": "A. V. Olinto\\thanksref{corr}"
}
] | The origin of the highest-energy cosmic rays remains a mystery. The lack of a high energy cutoff in the cosmic ray spectrum together with an apparently isotropic distribution of arrival directions have strongly constrained most models proposed for the generation of these particles. An overview of the present state of t... | [
{
"name": "physrepf.tex",
"string": "\\def\\la{\\hbox{{\\lower -2.5pt\\hbox{$<$}}\\hskip -8pt\\raise\n-2.5pt\\hbox{$\\sim$}}}\n\\def\\ga{\\hbox{{\\lower -2.5pt\\hbox{$>$}}\\hskip -8pt\\raise\n-2.5pt\\hbox{$\\sim$}}}\n\n\\documentstyle{elsart}\n\n\\begin{document}\n\\begin{frontmatter}\n\\title{ULTRA HIGH EN... | [
{
"name": "astro-ph0002006.extracted_bib",
"string": "\\begin{thebibliography}{9}\n\n\\bibitem{watson99} A. A. Watson, accompaning paper in this\nvolume (1999). \n\n\\bibitem{takeda98} M. Takeda et al., Phys. Rev. Lett.\n81 (1998) 1163. \n\n\\bibitem{takeda99} M. Takeda et al. preprint astro-ph/9902239\n(... |
astro-ph0002007 | [] | [
{
"name": "astro-ph0002007.tex",
"string": "\\documentstyle[12pt]{article}\n\\textheight 9in\n\\textwidth 6.5in\n\\bibliography{unsrt}\n\\renewcommand{\\baselinestretch}{2}\n\\begin{document}\n\\begin{center}\n{\\bf {\\Large {The Cosmological Quark-Hadron Transition and \\\\\nMassive Compact Halo Objects}}}... | [
{
"name": "astro-ph0002007.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\\bibitem{alcock} Alcock, C. {\\it et al.} (MACHO Collaboration) 1993, {\\it \nNature (London)} {\\bf {365}} 621\n\\bibitem{aubourg} Aubourg, E. {\\it et al.} (EROS Collaboration) 1993, {\\it\nNature (London)} {\\bf {365}} 6... | ||
astro-ph0002008 | ISO-SWS spectroscopy of NGC 1068 \footnote{Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.} | [
{
"author": "D.~Lutz\\footnote{Max-Planck-Institut f\\\"ur extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany}"
},
{
"author": "E.~Sturm$^2$"
},
{
"author": "R.~Genzel$^2$"
},
{
"author": "A.F.M.~Moorwood\\footnote{European Southern Observatory, Karl-Schwarzschild-Stra\\ss... | We present ISO-SWS spectroscopy of NGC 1068 for the complete wavelength range 2.4 to 45$\mu$m at resolving power $\sim$1500. Selected subranges have been observed at higher sensitivity and full resolving power $\sim$2000. We detect a total of 36 emission lines and derive upper limits for 13 additional transitions. Most... | [
{
"name": "obspaper.tex",
"string": "%\\documentstyle[12pt,aasms4]{article}\n\\documentstyle[11pt,aaspp4]{article}\n%\\documentstyle[aas2pp4]{article}\n\n%\\received{4 August 1988}\n%\\accepted{23 September 1988}\n%\\journalid{337}{15 January 1989}\n%\\articleid{11}{14}\n\\slugcomment{Accepted for publicati... | [
{
"name": "astro-ph0002008.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[Alexander et al. 1999]{alexander99} Alexander T., Sturm E., Lutz D., \n Sternberg A., Netzer H., Genzel R. 1999, \\apj, 512, 204\n\\bibitem[Alexander et al. 2000]{alexander00} Alexander T., et al., submitted to\n A... |
astro-ph0002009 | The giant radio galaxy 8C\,0821+695 and its environment | [
{
"author": "L. Lara\\inst{1}"
},
{
"author": "K.-H. Mack\\inst{2,3}"
},
{
"author": "M. Lacy\\inst{4}"
},
{
"author": "U. Klein\\inst{3}"
},
{
"author": "W.D. Cotton\\inst{5,6}"
},
{
"author": "L. Feretti\\inst{2}"
},
{
"author": "G. Giovannini\\inst{2,7}"
},
... | We present new VLA and Effelsberg observations of the radio galaxy 8C\,0821+695. We have obtained detailed images in total intensity and polarization of this 2 Mpc sized giant. The magnetic field has a configuration predominantly parallel to the source main axis. We observe Faraday rotation at low frequencies, most pro... | [
{
"name": "lara.tex",
"string": "%----------------------------------------------%\n% REFERENCES \n%----------------------------------------------%\n\\def\\aa{A\\&A} %Astronomy & Astrophysics%\n\\def\\aasup{A\\&AS} %A & A Supplements%\n\\def\\anj{AJ} %Astronomical Journal%\n\\def\\apj{ApJ} %Astrophysical Jou... | [
{
"name": "astro-ph0002009.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[1977]{baars} Baars J.M.W., Genzel R., Pauliny-Toth I.I.K., Witzel A.,\n1977, \\aa, 61, 99\n\n\\bibitem[1991]{barcons} Barcons X., Fabian A.C. \\& Rees M.J., 1991, Nature, \n350, 685\n\n\\bibitem[1984]{begelman2} Be... |
astro-ph0002010 | RADIATION SPECTRA FROM \\ADVECTION-DOMINATED ACCRETION FLOWS \\IN A GLOBAL MAGNETIC FIELD | [
{
"author": "MOTOKI KINO$^{1}$"
},
{
"author": "OSAMU KABURAKI and NAOHIRO YAMAZAKI"
}
] | We calculate the radiation spectra from advection-dominated accretion flows (ADAFs), taking into account the effects of a global magnetic field. Calculation is based on the analytic model for magnetized ADAFs proposed by Kaburaki, where a large-scale magnetic field controls the accretion process. Adjusting a few parame... | [
{
"name": "ms.tex",
"string": " \n%-----------------------------------------------------------------------------\n\n% 2nd Revised Manuscript\n%\n% Author(s): KINO, Motoki, KABURAKI, Osamu and YAMAZAKI, Naohiro \n% Title: RADIATION SPECTRA FROM ADVECTION-DOMINATED ACCRETION FLOWS \n% IN A GLOBAL MAGN... | [] |
astro-ph0002011 | \vglue-3.0truecm \centerline{\japit For submission to Monthly Notices} %\centerline{\japit Accepted for publication in Monthly Notices} \vglue 2.5truecm % \noindent Gravitational lens magnification by Abell 1689: Distortion of the background galaxy luminosity function | [
{
"author": "S. Dye$^1$"
},
{
"author": "A.N. Taylor$^1$"
},
{
"author": "E.M. Thommes$^{1,2}$"
},
{
"author": "K. Meisenheimer$^2$"
},
{
"author": "C. Wolf$^{\\,\\,2}$"
},
{
"author": "J.A. Peacock$^1$"
},
{
"author": "Royal Observatory"
},
{
"author": "B... | Gravitational lensing magnifies the observed flux of galaxies behind the lens. We use this effect to constrain the total mass in the cluster Abell 1689 by comparing the lensed luminosities of background galaxies with the luminosity function of an undistorted field. Under the assumption that these galaxies are a random ... | [
{
"name": "lumfn.tex",
"string": "\\documentstyle[twocolumn,epsfig]{mn}\n%\\documentstyle[referee]{mn}\n\\voffset -0.7truecm\n\\def\\bigstrut{\\vrule width0pt height0.6truecm}\n\\font\\japit = cmti10 at 10truept\n%\\smallskip\\noindent\n\\include{epsf}\n\n\\title\n [Lens magnification by Abell 1689: Bac... | [] |
astro-ph0002012 | Integrable models of galactic discs with double nuclei | [
{
"author": "P.O. Box 45195-159"
},
{
"author": "Gava Zang"
},
{
"author": "Zanjan"
},
{
"author": "IRAN"
}
] | We introduce a new class of 2-D mass models, whose potentials are of St\"ackel form in elliptic coordinates. Our model galaxies have two separate strong cusps that form double nuclei. The potential and surface density distributions are locally axisymmetric near the nuclei and become {highly} non-axisymmetric outside th... | [
{
"name": "paperJR.tex",
"string": "\\documentstyle[epsf]{mn}\n%\\textwidth= 16 cm\n%\\textheight= 9 in\n\\topmargin= -2.0 cm\n%\\headheight=0.0 mm\n%\\oddsidemargin=0 cm\n%\\evensidemargin=0 cm\n%\\def\\thefootnote{}\n%\\renewcommand{\\baselinestretch}{2}\n\\newcommand{\\noi}{\\noindent}\n%\\newcommand{\\t... | [
{
"name": "astro-ph0002012.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[R1]{BT87}Binney J., Tremaine S., 1987, Galactic Dynamics,\nPrinceton University Press, Princeton\n\\bibitem[R2]{dZ85}de Zeeuw P.T., 1985, MNRAS, 216, 273\n\\bibitem[R3]{GB85}Gerhard O.E., Binney J., 1985, MNRAS, 216,... |
astro-ph0002013 | CLUSTERING OF MASS AND GALAXIES | [
{
"author": "J.A. PEACOCK"
}
] | These lectures cover various aspects of the statistical description of cosmological density fields. Observationally, this consists of the point process defined by galaxies, and the challenge is to relate this to the continuous density field generated by gravitational instability in dark matter. The main topics discusse... | [
{
"name": "ini99.tex",
"string": "\\documentstyle[proceedings]{crckapb}\n\n%\n% JAP macros\n%\n\n\\let\\sec=\\section\n\\let\\ssec=\\subsection\n\\def\\half{{\\textstyle{\\scriptstyle 1\\over\\scriptstyle 2}}}\n\\def\\erf{{\\rm erf}}\n\\def\\japref{\\parskip=0pt\\par\\noindent\\hangindent\\parindent\n \\... | [] |
astro-ph0002014 | [] | [] | [] | ||
astro-ph0002015 | An extended multi-zone model for the MCG$-$6-30-15 warm absorber | [
{
"author": "\\parbox[]{6.in} {R. Morales$^1$, A.C.~Fabian$^1$ and C.S. Reynolds$^2$"
},
{
"author": "}"
}
] | The variable warm absorber seen with {\em ASCA} in the X-ray spectrum of MCG$-$6-30-15 shows complex time behaviour in which the optical depth of OVIII anticorrelates with the flux whereas that of OVII is unchanging. The explanation in terms of a two zone absorber has since been challenged by {\em BeppoSAX} observation... | [
{
"name": "paper.tex",
"string": "\\documentstyle[psfig]{mn}\n%\\documentstyle[astrobib,psfig]{mn-ab}\n\n% MNRAS reference abbreviations for control sequences generated by ADS. \n% Note that mnrasmnemonic is also needed in \\bibliography{}.\n\\def\\apj{ApJ}\n\\def\\apjl{ApJ}\n\\def\\apjs{ApJS}\n\\def\\mnras... | [
{
"name": "astro-ph0002015.extracted_bib",
"string": "\\begin{thebibliography}{}\n \n\\bibitem[\\protect\\citename{Baldwin et al.}1995]{bal95}\n Baldwin J., Ferland G., Korista K., Verner D., 1995, \\apjl,\n 455, L119\n\n\\bibitem[\\protect\\citename{Fabian et al.}1994]{fab94}\nFabian A.~C. et~al., 1994,... |
astro-ph0002016 | Understanding NLR in Seyfert Galaxies: numerical simulation of jet-cloud interaction | [
{
"author": "P.\\ Rossi\\inst{1}"
},
{
"author": "A.\\ Capetti \\inst{1}"
},
{
"author": "G.\\ Bodo\\inst{1}"
},
{
"author": "S.\\ Massaglia \\inst{2}"
},
{
"author": "A.\\ Ferrari\\inst{1,2}"
}
] | Recent HST observations suggest that the NLR in Seyfert Galaxies can be the result of interaction between jet and external inhomogeneous medium; following this suggestion we perform numerical simulations considering the impact of a radiative jet on a dense cloud. We approach the problem adopting a hydrodynamical code, ... | [
{
"name": "seyfert.tex",
"string": "%\\documentstyle[psfig,referee]{l-aa} % for a referee version\n\\documentstyle[psfig]{l-aa}\n\n%\\usepackage{graphics}\n%\\input psfig.sty\n\\def\\lapp{\\mathbin{\\raise2pt \\hbox{$<$} \\hskip-9pt \\lower4pt\n\\hbox{$\\sim$}}}\n\\def\\gapp{\\mathbin{\\raise2pt \\hbox{$>$}... | [
{
"name": "astro-ph0002016.extracted_bib",
"string": "\\begin{thebibliography}{} \n\n\\bibitem{}\nAllen M.G., Dopita M.A., Tsvetanov Z.I., Sutherland R.S., \n1999, ApJ 511, 686 \n\n\\bibitem{}\nAntonucci R.R.J., \n1993, ARA\\&A, 31, 473 \n\n\\bibitem{}\nAxon D.J., Capetti A., Macchetto, F.D., \n1999, ApJ ... |
astro-ph0002017 | X-Ray Wakes in Abell~160 | [
{
"author": "Nick Drake"
},
{
"author": "$^{1}$ Michael R. Merrifield"
},
{
"author": "$^{2}$ Irini Sakelliou$^{3}$ and Jason C. Pinkney$^{4}$"
},
{
"author": "$^{1}$Department of Physics and Astronomy"
},
{
"author": "Highfield"
},
{
"author": "Southampton SO17 1BJ"
},... | `Wakes' of X-ray emission have now been detected trailing behind a few (at least seven) elliptical galaxies in clusters. To quantify how widespread this phenomenon is, and what its nature might be, we have obtained a deep (70~ksec) X-ray image of the poor cluster Abell~160 using the ROSAT~HRI. Combining the X-ray data ... | [
{
"name": "a160.tex",
"string": "\\documentstyle[psfig]{mn}\n\\input epsf\n\n\\title[X-Ray Wakes in Abell~160]\n {X-Ray Wakes in Abell~160}\n\n\\author[N. Drake et al.]\n {Nick Drake,$^{1}$ Michael R. Merrifield,$^{2}$ Irini Sakelliou$^{3}$ \nand Jason C. Pinkney$^{4}$ \\\\ \n $^{1}$Department of Ph... | [
{
"name": "astro-ph0002017.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n \\bibitem[\\protect\\citename{Balsara et al. }1994]{balsara94}\n Balsara D., Livio M., O'Dea C. P., 1994, ApJ, 437, 83 \n \\bibitem[\\protect\\citename{Canizares, Fabbiano \\& Trinchieri \n}1987]{canizares87} \n Canizares... |
astro-ph0002018 | The HST view of the FR~I / FR~II dichotomy \thanks{Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555 and by STScI grant GO-3594.01-91A} | [
{
"author": "M. Chiaberge \\inst{1}"
},
{
"author": "A. Capetti \\inst{2}"
},
{
"author": "A. Celotti \\inst{1}"
}
] | In order to explore how the FR~I / FR~II dichotomy is related to the nuclear properties of radio galaxies, we studied a complete sample of 26 nearby FR~II radio galaxies using Hubble Space Telescope (HST) images and compared them with a sample of FR~I previously analyzed. FR~I nuclei lie in the radio-optical luminosity... | [
{
"name": "chiab.tex",
"string": "%\\documentclass[referee]{aa} % for a referee version\n\\documentclass{aa} \n\\usepackage{graphics} \n\\input psfig.sty \n\\newcommand{\\ltsima} {$\\; \\buildrel < \\over \\sim \\;$} \n\\newcommand{\\gtsima} {$\\; \\buildrel > \\over \\sim \\;$} \n\\newcommand{\\lta} {\\low... | [
{
"name": "astro-ph0002018.extracted_bib",
"string": "\\begin{thebibliography}{} \n\\bibitem[1985]{anto85} Antonucci R., Ulvestad J.S. 1985, ApJ 294, 158 \n\\bibitem[1985]{anto90} Antonucci R., Barvainis R. 1990, ApJ 363, L17 \n\\bibitem[1989]{bart89} Barthel P.D. 1989, ApJ 336, 606 \n\\bibitem[1996]{birett... |
astro-ph0002019 | Magnetized Atmospheres around Neutron Stars \\ Accreting at Low Rates | [
{
"author": "Silvia Zane"
}
] | We present a detailed investigation of atmospheres around accreting neutron stars with high magnetic field ($B\gtrsim 10^{12}$ G) and low luminosity ($L\lesssim 10^{33}$ erg/s). We compute the atmospheric structure, intensity and emergent spectrum for a plane--parallel, pure hydrogen medium by solving the transfer equa... | [
{
"name": "paper.tex",
"string": "%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n%%%%%%%%%\n% Preamble\n%%%%%%%%%\n%\\documentstyle[12pt,aasms4]{article} % <=== manuscript\n%\\documentstyle[11pt,aaspp4]{article} % <=== 1 column\n\\documentstyle[11pt,aaspp4,epsfig,psf... | [
{
"name": "astro-ph0002019.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\n\\bibitem[1973]{aw73:1973}\nAlme, W.L., \\& Wilson, J.R. 1973, \\apj, 186, 1015\n\n\\bibitem[1980]{al80:1980}\nArons, J., \\& Lea, S.M. 1980, \\apj, 235, 1016 \n\n\\bibitem[1987]{akl87:1987}\nArons, J., Klein, R.I., \\& Le... |
astro-ph0002020 | The ages of quasar host galaxies. | [
{
"author": "L.A. Nolan$^{1}$"
},
{
"author": "J.S. Dunlop$^{1}$"
},
{
"author": "M.J. Kukula$^{1}$"
},
{
"author": "D. H. Hughes$^{1,2}$"
},
{
"author": "T. Boroson$^{3}$ $\\&$ R. Jimenez$^{1}$."
},
{
"author": "Blackford Hill"
},
{
"author": "Edinburgh"
},
{... | We present the results of fitting deep off-nuclear optical spectra of radio-quiet quasars, radio-loud quasars and radio galaxies at $z \simeq 0.2$ with evolutionary synthesis models of galaxy evolution. Our aim was to determine the age of the dynamically dominant stellar populations in the host galaxies of these three ... | [
{
"name": "AGNhost.tex",
"string": "\\documentstyle[epsfig,graphics]{mn}\n\n\n\\def\\ls{{\\tiny \\( \\stackrel{<}{\\sim}\\)}} \n\\def\\gs{{\\tiny \\( \\stackrel{>}{\\sim}\\)}} \n\n\n\\begin{document}\n\n\\newcommand{\\etal}{{\\em et al.}\\ } % puts et al. in italics.\n\\newcommand{\\ie}{{\... | [] |
astro-ph0002021 | Optical off-nuclear spectra of quasar hosts and radio galaxies | [
{
"author": "David~H.~Hughes$^{1}$\\thanks{current address: INAOE, Apartado Postal 51 y 216, 7200, Puebla, Pue., Mexico}"
},
{
"author": "Marek~J.~Kukula$^{1}$"
},
{
"author": "James~S.~Dunlop$^{1}$ and Todd Boroson$^{2}$"
},
{
"author": "Department of Physics and Astronomy"
},
{
... | %\baselineskip=20pt We present optical ($\sim 3200$\AA~ to $\sim9000$\AA~) off-nuclear spectra of 26 powerful active galaxies in the redshift range $0.1 \leq z \leq 0.3$, obtained with the Mayall and William Herschel 4-meter class telescopes. The sample consists of radio-quiet quasars, radio-loud quasars (all with $-23... | [
{
"name": "mz862.tex",
"string": "\\documentstyle{mn}\n%\\documentstyle[referee]{mn}\n\n\\title[Quasar host galaxy spectra]{Optical off-nuclear spectra of quasar hosts and radio galaxies}\n\n\\author[D. H. Hughes et al.]\n{David~H.~Hughes$^{1}$\\thanks{current address: INAOE, Apartado Postal 51 y 216, 7200,... | [] |
astro-ph0002022 | The power spectral properties of the Z source GX~340+0 | [
{
"author": "Peter G. Jonker\\altaffilmark{1}"
},
{
"author": "Michiel van der Klis\\altaffilmark{1}"
},
{
"author": "Rudy Wijnands\\altaffilmark{1}$^{,}$\\altaffilmark{2}"
},
{
"author": "Jeroen Homan\\altaffilmark{1}"
},
{
"author": "Jan van Paradijs\\altaffilmark{1}$^{,}$\\alt... | \noindent We present an analysis of $\sim$390 ksec of data of the Z source GX~340+0 taken during 24 observations with the {\em Rossi\,X\,-ray\,Timing\,Explorer} satellite. We report the discovery of a new broad component in the power spectra. The frequency of this component varied between 9 and 14 Hz, and remained clos... | [
{
"name": "ms.tex",
"string": "\\documentstyle[psfig,11pt,emulateapj]{article}\n\n\\begin{document}\n\\title{The power spectral properties of the Z source GX~340+0}\n\\author{Peter G. Jonker\\altaffilmark{1}, Michiel van der\nKlis\\altaffilmark{1}, Rudy\nWijnands\\altaffilmark{1}$^{,}$\\altaffilmark{2}, Jer... | [
{
"name": "astro-ph0002022.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\\bibitem[Alpar \\& Shaham 1985]{alpar} Alpar, M.A., Shaham, J. 1985,\nNature 316, 239 \n\\bibitem[Belloni et al. (1997)]{belloni} Belloni, T., van der Klis,\nM., Lewin, W.H.G., van Paradijs, J., Dotani, T., Mitsuda, K., \\&... |
astro-ph0002023 | The relativistic iron line profile in the Seyfert 1 Galaxy IC4329a | [
{
"author": "C. Done$^1$"
},
{
"author": "G.M. Madejski$^2$"
},
{
"author": "P.T. \\.{Z}ycki$^3$"
}
] | We present simultaneous ASCA and RXTE data on the bright Seyfert 1 galaxy IC4329a. The iron line is significantly broadened, but not to the extent expected from an accretion disk which extends down to the last stable orbit around a black hole. We marginally detect a narrow line component, presumably from the molecular ... | [
{
"name": "ms.tex",
"string": "%&latex209 \n%\\documentstyle[epsf,emulateapj]{article}\n\\documentstyle[11pt,epsf,aaspp4]{article}\n\\def\\Rin{R_{\\rm in}}\n\\def\\Rg{R_{\\rm g}}\n\\def\\Rs{R_{\\rm s}}\n\\def\\mdot{{\\dot m}}\n\\def\\mdcrit{{\\dot m}_{\\rm crit}}\n\\def\\msun{M_{\\odot}}\n\\def\\dm{{\\dot m... | [] |
astro-ph0002024 | ISO-LWS spectroscopy of Centaurus A: extended star formation | [
{
"author": "S. J. Unger \\inst{1}"
},
{
"author": "P. E. Clegg \\inst{1}"
},
{
"author": "G. J. Stacey \\inst{2}"
},
{
"author": "P. Cox \\inst{3}"
},
{
"author": "J. Fischer \\inst{4}"
},
{
"author": "M. Greenhouse \\inst{5}"
},
{
"author": "S. D. Lord \\inst{6}... | We present the first full FIR spectrum of Centaurus A (NGC 5128) from 43 - 196.7 $\mu$m. The data was obtained with the ISO Long Wavelength Spectrometer (LWS). We conclude that the FIR emission in a 70~\arcsec~beam centred on the nucleus is dominated by star formation rather than AGN activity. The flux in the far-infra... | [
{
"name": "h1733.tex",
"string": "%\\documentstyle[referee,epsfig]{l-aa}\n\\documentstyle[epsfig]{l-aa}\n% some abbreviations\n%\n\\def\\ha{H$\\alpha$ }\n\\def\\eg{{\\it e.g.\\ }}\n\\def\\ie{{\\it i.e.\\ }}\n%\\def\\etal{{\\it et al.\\ }}\n\\def\\h0{{\\rm H_0}}\n\\def\\mum{\\mu {\\rm\\,m}}\n\\def\\pm{^+_-}\... | [
{
"name": "astro-ph0002024.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\section*{References}\n\nColbert J.W., Malkan M.A., Clegg P.E., et al., 1999, ApJ 511, 721 \\\\\n%Cunningham C.T., Ade, P.A.R., Robson, E.I. et al.,\n%1984, MNRAS 211, 543\\\\\nEckart A., Cameron M., Rothermel H., et al., 199... |
astro-ph0002025 | First results of the air shower experiment KASCADE | [
{
"author": "T.~Antoni$^{a}$"
},
{
"author": "W.D.~Apel$^{a}$"
},
{
"author": "K.~Bekk$^{a}$"
},
{
"author": "K. Bernl{\\\"o}hr$^{a}$"
},
{
"author": "H.~Bl\\\"umer$^{a,d}$"
},
{
"author": "E.~Bollmann$^{a}$"
},
{
"author": "H.~Bozdog$^{b}$"
},
{
"author":... | The main goals of the KASCADE (KArlsruhe Shower Core and Array DEtector) experiment are the determination of the energy spectrum and elemental composition of the charged cosmic rays in the energy range around the knee at $\approx 5\,$PeV. Due to the large number of measured observables per single shower a variety of di... | [
{
"name": "taup.tex",
"string": "\\documentclass[twoside]{article}\n\\usepackage{fleqn,espcrc2}\n\\usepackage{graphicx}\n\\hyphenation{author another created financial paper \nre-commend-ed Post-Script CORSIKA KASCADE SIBYLL\nForschungs-zentrum}\n\\renewcommand{\\bottomfraction}{0.999}\n\\renewcommand{\\top... | [
{
"name": "astro-ph0002025.extracted_bib",
"string": "\\begin{thebibliography}{9}\n\\bibitem{klages} \nH.O. Klages et al. -- KASCADE collaboration, \nNucl. Phys. B (Proc. Suppl.) 52B (1997) 92. \n\\bibitem{cors}\nD. Heck et al., FZKA 6019, Forschungszentrum Karlsruhe (1998).\n\\bibitem{slc}\nT. Antoni et al... |
astro-ph0002026 | Mass-loss induced instabilities in fast rotating stars | [
{
"author": "F. Ligni\\`eres \\inst{1,} \\inst{2}"
},
{
"author": "C. Catala \\inst{3}"
},
{
"author": "A. Mangeney \\inst{2}"
}
] | To explain the origin of Herbig Ae/Be stars activity, it has been recently proposed that strong mass-losses trigger rotational instabilities in the envelope of fast rotating stars. The kinetic energy transferred to turbulent motions would then be the energy source of the active phenomena observed in the outer atmospher... | [
{
"name": "rot.soum.tex",
"string": "\\documentclass{aa}\n%\\documentclass{aa}\n\\usepackage{graphics}\n\\begin{document}\n \n\\thesaurus{02.(02.09.1)08.(08.13.2;08.18.1)}\n \n\\title{Mass-loss induced\ninstabilities\nin fast rotating stars}\n\\author{F. Ligni\\`eres \\inst{1,} \\inst{2} \\and C. Catala \\i... | [
{
"name": "astro-ph0002026.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem {1} Bouret J.-C., Catala C., 1998, A\\&A 340, 163\n\\bibitem {2} Balbus S.A., Hawley J.F., Stone J.M., 1996, ApJ 467, 76\n\\bibitem {6} Catala C., Felenbok P., Czarny J., Talavera A., \nBoesgaard A.M., 1986, ApJ 308,... |
astro-ph0002027 | % article title \bgroup \vbox to 8pt{\vss}% \seventeenpoint \Raggedright \noindent \strut{#1}\par \egroup | [
{
"author": "% article author(s) \\bgroup \\ifnum\\LastMac=\\Afe \\OneHalf\\else \\vskip 21pt\\fi \\fourteenpoint \\Raggedright \\noindent \\strut #1\\par \\vskip 3pt% \\egroup"
}
] | % \bgroup \vskip 20pt% \leftskip 11pc\rightskip\z@ \noindent{\ninebf ABSTRACT}\par \tenpoint \Fullout \noindent #1\par \egroup | [
{
"name": "mn.tex",
"string": "% MN.TEX (Computer Modern version)\n%\n% plain TeX single / double column macros for the\n% Monthly Notices of Royal Astronomical Society\n%\n% v1.6 (mn.tex) --- released 18th September 1995 (A. Woollatt)\n% v1.5 \" --- released 25th August 1994 (M. Reed)\n% v1.4 ... | [
{
"name": "astro-ph0002027.extracted_bib",
"string": "\\bibitem=\\bib@item\n}\n\n\\def\\bib@item{%\n \\par\\parindent=1.5em\\Hang{1.5em}{1}%\n \\everypar={\\Hang{1.5em}{1}\\ignorespaces}%\n \\noindent\\ignorespaces\n}\n\n\\def\\endrefs{\\par\\egroup\\@doendpe}\n\n\n% Page heads\n\n\\newtoks\\CatchLine\n\... |
astro-ph0002028 | ChaMP and the High Redshift Quasars in X-rays | [
{
"author": "S. Mathur\\altaffilmark{1}"
}
] | -- | [
{
"name": "reform.tex",
"string": "% PSAMPLE2.TEX -- PASP Conference Proceedings macro package tutorial paper.\n\n% Lines starting with \"%\" are comments; they will be ignored by LaTeX.\n\n% This is a comprehensive example, meaning thyat we have made use of each\n% of the capabilities of the LaTeX + the PA... | [] |
astro-ph0002029 | High-resolution simulations and visualization of protoplanetary disks | [
{
"author": "Pawe{\\l} Cieciel\\c{a}g"
},
{
"author": "Tomasz Plewa"
},
{
"author": "Micha{\\l} R\\'o\\.zyczka"
}
] | A problem of mass flow in the immediate vicinity of a planet embedded in a protoplanetary disk is studied numerically in two dimensions. Large differences in temporal and spatial scales involved suggest that a specialized discretization method for solution of hydrodynamical equations may offer great savings in computat... | [
{
"name": "dppn.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n%\n%\n%\n\\markboth{Cieciel\\c{a}g, Plewa, R\\'o\\.zyczka}\n{High-resolution simulations and visualization of protoplanetary disks}\n\n\\pagestyle{myheadings}\n\n\\begin{document}\n\\title{High-resolution simulations and v... | [] |
astro-ph0002030 | COSMIC DEFECTS AND COSMOLOGY | [
{
"author": "JO\\~AO MAGUEIJO"
}
] | We provide a pedagogical overview of defect models of structure formation. We first introduce the concept of topological defect, and describe how to classify them. We then show how defects might be produced in phase transitions in the Early Universe and approach non-pathological scaling solutions. A very heuristic acco... | [
{
"name": "defects1.tex",
"string": "\\documentstyle[editedvolume,numreferences,epsf]{crckapb} \n\\input psfig\n\\newcommand{\\stt}{\\small\\tt}\n\\newcommand{\\be}{\\begin{equation}}\n\\newcommand{\\ee}{\\end{equation}}\n\n\\def\\al{\\alpha} \n\n\\def\\ga{\\gamma}\n\\def\\de{\\delta}\n\\def\\ep{\\epsilon}... | [
{
"name": "astro-ph0002030.extracted_bib",
"string": "\\begin{thebibliography}{10} \n\n\\bibitem{TK80} T.W.G. Kibble, {\\it Phys. Rep.} {\\bf 67}, 183 (1980).\n\\bibitem{Vil85} A. Vilenkin, {\\it Phys. Rep.} {\\bf 121}, 263 (1985).\n\\bibitem{ShellVil} A. Vilenkin and E.P.S. Shellard, `Strings and Other To... |
astro-ph0002031 | The Role of H$_{2}$ Molecules in Cosmological Structure Formation | [
{
"author": "T. Abel$^1$"
},
{
"author": "\\ns Z. Haiman$^2$\\footnote{Hubble Fellow}"
}
] | We review the relevance of ${H_2}$ molecules for structure formation in cosmology. Molecules are important at high--redshifts, when the first collapsed structures appear with typical temperatures of a few hundred Kelvin. In these chemically pristine clouds, radiative cooling is dominated by ${H_2}$ molecules. As a resu... | [
{
"name": "h2rev.tex",
"string": "\\documentstyle[english,psfig]{cupconf}\n\n% use these four lines when finally presenting your CRC. (See Appendix B\n% of the guide.)\n%\\magnification 1200 % always use 1200 when presenting your chapter\n%\\oddsidemargin -0.5pc % appropriate for A4, you may need to v... | [
{
"name": "astro-ph0002031.extracted_bib",
"string": "\\begin{thebibliography}{} \n\n\\bibitem[Abel 1995]{Abel95} {\\sc Abel, T.} 1995, {\\it Thesis}, University of\nRegensburg, Germany \n\n\\bibitem[Abel et al. (1997)]{Abel97} {\\sc Abel, T., Anninos, P.,\nZhang, Y., Norman, M. L.} 1997, {\\it NewA} {\\... |
astro-ph0002032 | The Fading of Supernova Remnant Cassiopeia A from 38 MHz to 16.5 GHz from 1949 to 1999 with New Observations at 1405 MHz\altaffilmark{1} | [
{
"author": "Daniel E. Reichart\\altaffilmark{2} and Andrew W. Stephens\\altaffilmark{3}"
}
] | We report 1405 MHz measurements of the flux density of the $\approx 320$ year old supernova remnant Cassiopeia A, relative to the flux density of Cygnus A, made between 1995 and 1999. When compared to measurements made between 1957 and 1976, we find that the rate at which Cassiopeia A has been fading at this and nearby... | [
{
"name": "casb.tex",
"string": "%\\documentstyle[12pt,aasms4]{article}\n\\documentstyle[11pt,aaspp4]{article}\n%\\documentstyle[aaspptwo]{article}\n\n%\\tighten\n%\\eqsecnum\n\n\\def\\la{\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\hbox{$\\sim$}}}\\hbox{$<$}}}}\n\\def\\ga{\\mathrel{\\hbox{\\rlap{\\hbox{\\low... | [
{
"name": "astro-ph0002032.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[Agafonov 1996]{a96}\nAgafonov, M. I. 1996, A\\&A, 306, 578\n\n\\bibitem[Ashworth 1980]{a80}\nAshworth, W. B. 1980, J. Hist. Astr., 11, 1\n\n\\bibitem[Baily 1835]{b35}\nBaily, F. 1835, An account of the Revd. John F... |
astro-ph0002033 | Multiwavelength Observations of the Second Largest Known FR II Radio Galaxy, NVSS 2146+82 | [
{
"author": "Christopher Palma\\altaffilmark{1}"
},
{
"author": "Franz E. Bauer\\altaffilmark{2}"
}
] | We present multi-frequency VLA, multicolor CCD imaging, optical spectroscopy, and {ROSAT} HRI observations of the giant FR II radio galaxy NVSS 2146+82. This galaxy, which was discovered by the NRAO VLA Sky Survey (NVSS), has an angular extent of nearly 20\arcmin\ from lobe to lobe. The radio structure is normal for an... | [
{
"name": "Palmaep.tex",
"string": "\\documentstyle[12pt,aaspp4]{article}\n\\begin{document}\n\n\\title{\\bf Multiwavelength Observations of the Second Largest Known\nFR II Radio Galaxy, NVSS 2146+82}\n\\author{Christopher Palma\\altaffilmark{1}, Franz E. Bauer\\altaffilmark{2}}\n\\affil{Department of Astro... | [
{
"name": "astro-ph0002033.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[Abell 1958]{abell} Abell, G. O. 1958, \\apjs, 3, 211 \n\n\\bibitem[Allington-Smith et al.\\ 1993]{aezo} Allington-Smith, J. R.,\nEllis, R. S., Zirbel, E. L., \\& Oemler, A., 1993, \\apj, 404, 521 \n\n\\bibitem[Berk... |
astro-ph0002034 | The Detectability of Gamma-Ray Bursts and Their Afterglows at Very High Redshifts | [
{
"author": "Donald Q. Lamb and Daniel E. Reichart"
}
] | There is increasingly strong evidence that gamma-ray bursts (GRBs) are associated with star-forming galaxies, and occur near or in the star-forming regions of these galaxies. These associations provide indirect evidence that at least the long GRBs detected by BeppoSAX are a result of the collapse of massive stars. The ... | [
{
"name": "grb_highz.tex",
"string": "\\documentstyle[psfig]{aipproc}\n\n\\def\\la{\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\hbox{$\\sim$}}}\\hbox{$<$}}}}\n\\def\\ga{\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\hbox{$\\sim$}}}\\hbox{$>$}}}}\n\n\\begin{document}\n\\title{The Detectability of Gamma-Ray Bursts ... | [
{
"name": "astro-ph0002034.extracted_bib",
"string": "\\bibitem{mpp00}\nMazzoli, R. S., Pendleton, G. N., \\& Paciesas, W. S. 1996, ApJ, 471, 636\n\n\\bibitem{lr00}\nLamb, D. Q., \\& Reichart, D. E., 2000, ApJ, in press (astro-ph/9909002)\n\n\\bibitem{mea93}\nMeegan, C. A., et al. 1993, Second BATSE Catalog... |
astro-ph0002035 | Gamma-Ray Bursts as a Probe of the Very High Redshift Universe | [
{
"author": "Donald Q. Lamb and Daniel E. Reichart"
}
] | We show that, if many GRBs are indeed produced by the collapse of massive stars, GRBs and their afterglows provide a powerful probe of the very high redshift ($z \gtrsim 5$) universe. | [
{
"name": "T-32.tex",
"string": "\\documentstyle[psfig]{aipproc}\n\n\\def\\la{\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\hbox{$\\sim$}}}\\hbox{$<$}}}}\n\\def\\ga{\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\hbox{$\\sim$}}}\\hbox{$>$}}}}\n\n\\begin{document}\n\\title{Gamma-Ray Bursts as a Probe of the Very Hig... | [
{
"name": "astro-ph0002035.extracted_bib",
"string": "\\bibitem{cl99}\nCastander, F. J., \\& Lamb, D. Q. 1999, ApJ, 523, 593 \n\n\\bibitem{fea99a}\nFruchter, A. S., et al. 1999, ApJ, 516, 683 \n\n\\bibitem{kea98}\nKulkarni, S. R., et al. 1998, Nature, 395, 663\n\n\\bibitem{f99}\nFruchter, A. S. 1999, ApJ, 5... |
astro-ph0002036 | The Merger Rate to Redshift One from Kinematic Pairs: \\ Caltech Faint Galaxy Redshift Survey XI | [
{
"author": "R.~G.~Carlberg\\altaffilmark{1,2}"
},
{
"author": "Judith~G.~Cohen\\altaffilmark{3}"
},
{
"author": "D.~R.~Patton\\altaffilmark{1,2}"
},
{
"author": "Roger~Blandford\\altaffilmark{4}"
},
{
"author": "David~W.~Hogg\\altaffilmark{5,6}"
},
{
"author": "H.~K.~C.~... | The rate of mass accumulation due to galaxy merging depends on the mass, density, and velocity distribution of galaxies in the near neighborhood of a host galaxy. The fractional luminosity in kinematic pairs combines all of these effects in a single estimator which is relatively insensitive to population evolution. Her... | [
{
"name": "merger.tex",
"string": "\\def\\km{{\\rm\\,km}}\n\\def\\cms{{\\rm\\,cm\\,s^{-1}}}\n\\def\\kms{\\ifmmode{\\,\\hbox{km}\\,s^{-1}}\\else {\\rm\\,km\\,s$^{-1}$}\\fi}\n\\def\\kpc{{\\rm\\,kpc}}\n\\def\\mpc{{\\rm\\,Mpc}}\n\\def\\msun{{\\rm\\,M_\\odot}}\n\\def\\lsun{{\\rm\\,L_\\odot}}\n\\def\\rsun{{\\rm\\... | [
{
"name": "astro-ph0002036.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[Barnes \\& Hernquist 1992]{bh} Barnes, J. E. \\& \n\tHernquist, L. 1992, \\araa, 30, 705 \n\\bibitem[Carlberg Pritchet \\& Infante 1994]{cpi}\n Carlberg, R. G., Pritchet, C. J., \\& Infante, L. 1994, \\apj, 4... |
astro-ph0002037 | Gravitational Clustering from $\chi^2$ Initial Conditions | [
{
"author": "Rom\\'{a}n Scoccimarro"
}
] | We consider gravitational clustering from primoridal non-Gaussian fluctuations provided by a $\chi^2$ model, as motivated by some models of inflation. The emphasis is in signatures that can be used to constrain this type of models from large-scale structure galaxy surveys. Non-Gaussian initial conditions provide additi... | [
{
"name": "chisq.tex",
"string": "\\documentstyle[aaspp4,tighten,flushrt]{article}\n%\\documentstyle[11pt,aasms4,tighten]{article}\n\n\\newcommand{\\beq}{\\begin{equation}}\n\\newcommand{\\eeq}{\\end{equation}}\n\\newcommand{\\beqa}{\\begin{eqnarray}}\n\\newcommand{\\eeqa}{\\end{eqnarray}}\n\n\\def\\eq#1{eq... | [
{
"name": "astro-ph0002037.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\n\\bibitem{AMM97} Antoniadis I., Mazur P. O., Mottola E. 1997, \\prl,\n79, 14\n\n\\bibitem{BCHJ95} Bouchet F.R., Colombi S., Hivon E., Juszkiewicz\nR. 1995, \\aap, 296, 575\n\n\\bibitem{BMW94} Buchert T., Melott A. L., Wei... |
astro-ph0002038 | A Search for Resonant Structures in the Zodiacal Cloud with COBE DIRBE: The Mars Wake and Jupiter's Trojan Clouds | [
{
"author": "Marc J. Kuchner"
}
] | We searched the COBE DIRBE Sky and Zodi Atlas for a wake of dust trailing Mars and for Trojan dust near Jupiter's L5 Lagrange point. We compare the DIRBE images to a model Mars wake based on the empirical model of the Earth's wake as seen by the DIRBE and place a 3-$\sigma$ upper limit on the fractional overdensity of ... | [
{
"name": "paper.tex",
"string": "\\documentstyle[12pt,aaspp4]{article}\n\\lefthead{Kuchner, Reach and Brown}\n\\righthead{Resonant Structures in the Zodiacal Cloud with DIRBE}\n\\begin{document}\n\n\\title{A Search for Resonant Structures in the Zodiacal Cloud with COBE DIRBE: The Mars Wake and Jupiter's T... | [] |
astro-ph0002039 | Keck Speckle Imaging of the White Dwarf G29-38: No Brown Dwarf Companion Detected | [
{
"author": "Marc J. Kuchner"
},
{
"author": "Christopher D. Koresko"
},
{
"author": "and Michael E. Brown\\altaffilmark{1}"
}
] | The white dwarf Giclas 29-38 has attracted much attention due to its large infrared excess and the suggestion that excess might be due to a companion brown dwarf. We observed this object using speckle interferometry at the Keck telescope, obtaining diffraction-limited resolution (55 milliarcseconds) at K band, and foun... | [
{
"name": "paper.tex",
"string": "% Incorporating comments from Ben Zuckerman\n\\documentstyle[12pt,aaspp4]{article}\n\\begin{document}\n\n\\title{Keck Speckle Imaging of the White Dwarf G29-38: No Brown Dwarf Companion Detected}\n\\author{Marc J. Kuchner, Christopher D. Koresko, and Michael E. Brown\\altaf... | [] |
astro-ph0002040 | An 11.6 Micron Keck Search For Exo-Zodiacal Dust | [
{
"author": "Marc J. Kuchner"
},
{
"author": "Michael E. Brown and Chris D. Koresko"
}
] | We have begun an observational program to search nearby stars for dust disks that are analogous to the disk of zodiacal dust that fills the interior of our solar system. We imaged six nearby main-sequence stars with the Keck telescope at 11.6 microns, correcting for atmosphere-induced wavefront aberrations and deconvol... | [
{
"name": "paper.tex",
"string": "\n\\documentstyle[12pt,aaspp4]{article}\n\\begin{document}\n\n\\title{An 11.6 Micron Keck Search For Exo-Zodiacal Dust}\n\\author{Marc J. Kuchner, Michael E. Brown and Chris D. Koresko}\n\\affil{California Institute of Technology, Pasadena, CA 91125}\n\\authoremail{mjk@gps.... | [] |
astro-ph0002041 | Cosmic Ray Rejection by Linear Filtering of Single Images\footnote{ Accepted for publication in the May 2000 issue of the {Publications of the Astronomical Society of the Pacific.} } | [
{
"author": "James E. Rhoads"
}
] | We present a convolution-based algorithm for finding cosmic rays in single well-sampled astronomical images. The spatial filter used is the point spread function (approximated by a Gaussian) minus a scaled delta function, and cosmic rays are identified by thresholding the filtered image. This filter searches for featur... | [
{
"name": "crrej_eprint.tex",
"string": "% Manuscript of a PASP paper outlining our cosmic ray rejection formalism.\n% writeup started 24 July 1999\n% last modification before submission July 29\n% First revisions based on referee's report Nov 10-11\n% Further revisions Dec 6- based on results of Artificial... | [] |
astro-ph0002042 | The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks | [
{
"author": "Yutaka Fujita\\altaffilmark{1} and Fumio Takahara"
}
] | We investigate the origin of the variation of the gas mass fraction in the core of galaxy clusters, which was indicated by our work on the X-ray fundamental plane. Applying a spherical collapse model of cluster formation and considering the effect of shocks on preheated intracluster gas, we construct a simple model to ... | [
{
"name": "ms_prep1.tex",
"string": "%#!latex\n%\\documentclass{aastex}\n\\documentclass[preprint]{aastex}\n\\slugcomment{OU-TAP 115: ApJ in press}\n\n\\shorttitle{Variation of Gas Mass Distribution in Galaxy Clusters}\n\n\n\\begin{document}\n\n\\title{The Variation of Gas Mass\nDistribution in Galaxy Clust... | [
{
"name": "astro-ph0002042.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n%\\bibitem[Bahcall and Lubin(1994)]{bah94}Bahcall, N. A., Lubin,\n% L. M. 1994, \\apj, 426, 513\n\n\\bibitem[Arnaud and Evrard(1999)]{arn99}Arnaud, M., Evrard, A. E. 1999,\n\\mnras, 305, 631\n\n\\bibitem[Balogh et al.(1999)]... |
astro-ph0002043 | A Search for Exozodiacal Dust and Faint Companions Near Sirius, Procyon, and Altair with the NICMOS Coronagraph\altaffilmark{1} | [
{
"author": "Marc J. Kuchner"
}
] | We observed Sirius, Altair, and Procyon with the NICMOS Coronagraph on the Hubble Space Telescope to look for scattered light from exo-zodiacal dust and faint companions within 10 AU from these stars. We did not achieve enough dynamic range to surpass the upper limits set by IRAS on the amount of exo-zodiacal dust in t... | [
{
"name": "paper.tex",
"string": "\\documentstyle[12pt,aaspp4]{article}\n%\\documentstyle[12pt,aasms4]{article}\n\\begin{document}\n\n\\title{A Search for Exozodiacal Dust and Faint Companions Near Sirius,\nProcyon, and Altair with the NICMOS Coronagraph\\altaffilmark{1}}\n\\author{Marc J. Kuchner}\n\\affil... | [] |
astro-ph0002044 | [] | [
{
"name": "review.tex",
"string": "\\documentclass{elsart} %{article}\n%21 pages becomes 17 without the [12pt] - default appears to be 10pt\n%\\usepackage{elsart,}\n%\\usepackage{psfig,natbib}\n\\usepackage{epsf,graphics,natbib}\n\\begin{document}\n\\def\\fdg{\\hbox{$.\\!\\!^\\circ$}}\n\\def\\mycaption#1{\... | [
{
"name": "review.bbl",
"string": "\\begin{thebibliography}{126}\n\\expandafter\\ifx\\csname natexlab\\endcsname\\relax\\def\\natexlab#1{#1}\\fi\n\n\\bibitem[{{Aghanim} {et~al.}(1996){Aghanim}, {Desert}, {Puget}, \\&\n {Gispert}}]{aghanimetal96}\n{Aghanim}, N., {Desert}, F.~X., {Puget}, J.~L., \\& {Gispert... | ||
astro-ph0002045 | Conservation of circulation in magnetohydrodynamics | [] | We demonstrate, both at the Newtonian and (general) relativistic levels, the existence of a generalization of Kelvin's circulation theorem (for pure fluids) which is applicable to perfect magnetohydrodynamics. The argument is based on the least action principle for magnetohydrodynamic flow. Examples of the new conserva... | [
{
"name": "astro-ph0002045.tex",
"string": "\\documentstyle[aps,pre,eqsecnum,12pt]{revtex}\n\n\\begin{document}\n\\tighten\n\\title{Conservation of circulation in magnetohydrodynamics }\n\n \\author{ Jacob D. Bekenstein\\thanks{Electronic mail:\n bekenste@vms.huji.ac.il} and Asaf\nOron\\thanks{Electroni... | [
{
"name": "astro-ph0002045.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\n\\bibitem{bekenstein1}J. D. Bekenstein and E. Oron, Phys. Rev. D {\\bf\n18},1809 (1978).\n\n\\bibitem{bekenstein2}J. D. Bekenstein, Astrophys, Journ. {\\bf 319}, 207\n(1987).\n\n\\bibitem{herivel}J. W. Herivel, Proc. Camb.... |
astro-ph0002046 | Effects of massive star formation on the ISM of dwarf galaxies | [
{
"author": "Suzanne C. Madden"
}
] | We are studying star formation effects on the properties of the ISM in low metallicity environments using mid-infrared (MIR) and far-infrared (FIR) observations of starbursting dwarf galaxies taken with the Infrared Space Observatory (ISO) and the Kuiper Airborne Observatory (KAO). Effects of the hard pervasive radiati... | [
{
"name": "toulouse.tex",
"string": "\\documentclass{elsart}\n%\\usepackage{natbib}\n\\usepackage{graphicx}\n\\begin{document}\n\\runauthor{Madden}\n\\begin{frontmatter}\n%\\title{Effects of massive star formation on the ISM of dwarf galaxies}\n\\title{Effects of massive star formation on the ISM of dwarf g... | [
{
"name": "astro-ph0002046.extracted_bib",
"string": "\\begin{thebibliography}{999}\n\\bibitem{kessler96} M.F. Kessler et al., {\\em A\\&A\\/} {\\bf 315} (1996) L27.\n\\bibitem{jones97} A.P. Jones, S.C. Madden, S.W.J. Colgan, N. Geis, M. Haas, P. Maloney, T. Nikola, A. Poglitsch, {\\em Extragalactic Astrono... |
astro-ph0002047 | THE PRIMORDIAL HELIUM ABUNDANCE: TOWARDS UNDERSTANDING AND REMOVING THE COSMIC SCATTER IN THE $dY/dZ$ RELATION | [
{
"author": "D. R. Ballantyne\\altaffilmark{1}"
},
{
"author": "G. J. Ferland\\altaffilmark{2} and P. G. Martin"
}
] | We present results from photoionization models of low-metallicity \h regions. These nebulae form the basis for measuring the primordial helium abundance. Our models show that the helium ionization correction factor (ICF) can be non-negligible for nebulae excited by stars with effective temperatures larger than 40,000~K... | [
{
"name": "ms.tex",
"string": "\\documentclass[preprint]{aastex}\n\n\\newcommand{\\h}{H\\scriptsize II \\normalsize}\n\\newcommand{\\etal}{et al.}\n\\newcommand{\\3}{[O III]~$\\lambda$5007}\n\\newcommand{\\1}{[O I]~$\\lambda$6300}\n\n\\begin{document} \n\n\\title{THE PRIMORDIAL HELIUM ABUNDANCE: ... | [
{
"name": "astro-ph0002047.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[Armour \\etal (1999)]{arm99} Armour, M-H., Ballantyne, D. R., \nFerland, G. J., Karr, J. \\& Martin, P. G. 1999, \\pasp, 111, 1251.\n\\bibitem[Benjamin, Skillman \\& Smits(1999)]{ben99} Benjamin, R. A., Skillman, E. ... |
astro-ph0002048 | center | [
{
"author": "center"
}
] | The calculations in Thomas-Fermi approximation show that in a gravitational field each cell of ultra dense matter inside celestial bodies obtains a very small positive electric charge. A celestial body is electrically neutral as a whole, because the negative electric charge exists on its surface. On the order of magnit... | [
{
"name": "MM-star.tex",
"string": "\\documentstyle[epsfig,12pt]{article}\n %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n\n\\begin{document}\n Submitted to \"Il Nuovo Cimento C\"\n\\begin{center}\n\n{\\bf\n\n\\ti... | [
{
"name": "astro-ph0002048.extracted_bib",
"string": "\\begin{thebibliography}{18}\n\n\\bibitem {1} Borra E.F. and Landstreet J.D. - The Astrophysical Journ, Suppl., 1980, v.42, 421-445.\n\\bibitem {2} Beskin V.S.,Gurevich, A.V., Istomin Ya.N. - Physics of the Pulsar Magnetosphere, Cambridge University ... |
astro-ph0002049 | Compton dragged gamma--ray bursts: the spectrum | [
{
"author": "Gabriele Ghisellini$^1$"
},
{
"author": "Davide Lazzati"
},
{
"author": "$^{1,2}$ Annalisa Celotti$^3$ and Martin J. Rees$^{4}$"
},
{
"author": "$^1$ Osservatorio Astronomico di Brera"
},
{
"author": "Via Bianchi 46"
},
{
"author": "I--23807 Merate (Lc)"
},... | We calculate the spectrum resulting from the interaction of a fireball with ambient soft photons. These photons are assumed to be produced by the walls of a funnel in a massive star. By parameterizing the radial dependence of the funnel temperature we calculate the deceleration of the fireball self--consistently, takin... | [
{
"name": "ghisellini.tex",
"string": "\\documentstyle[psfig]{mn}\n\n\\def\\ltsima{$\\; \\buildrel < \\over \\sim \\;$}\n\\def\\lsim{\\lower.5ex\\hbox{\\ltsima}}\n\\def\\gtsima{$\\; \\buildrel > \\over \\sim \\;$}\n\\def\\gsim{\\lower.5ex\\hbox{\\gtsima}}\n\n\\begin{document}\n\n\\title[Compton dragged gamm... | [
{
"name": "astro-ph0002049.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem []{} Crider A. et al., 1997, ApJ, 479, L39\n\\bibitem []{} Ghisellini G., Celotti A., 1999, ApJ, 511, L93 \n\\bibitem []{} Granot J., Piran T., Sari R., 2000, ApJ, 534, L163\n\\bibitem []{} Kumar P., 1999, ApJ, 523, ... |
astro-ph0002050 | A Test of the Collisional Dark Matter Hypothesis from Cluster Lensing | [
{
"author": "Jordi Miralda-Escud\\'e$^{1}$"
}
] | Spergel \& Steinhardt proposed the possibility that the dark matter particles are self-interacting, as a solution to two discrepancies between the predictions of cold dark matter models and the observations: first, the observed dark matter distribution in some dwarf galaxies has large, constant-density cores, as oppose... | [
{
"name": "p62b.tex",
"string": "\\documentclass[12pt,preprint]{aastex}\n%\\documentstyle[11pt,aaspp4]{article}\n\\begin{document}\n\\newcommand{\\msun}{M_{\\odot}}\n\\newcommand{\\kms}{\\, {\\rm km\\, s}^{-1}}\n\\newcommand{\\cm}{\\, {\\rm cm}}\n\\newcommand{\\gm}{\\, {\\rm g}}\n\\newcommand{\\gev}{\\, {\\... | [
{
"name": "astro-ph0002050.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[Bahcall et al. 1999]{bops99}\nBahcall, N., Ostriker, J. P.,\nPerlmutter, S., \\& Steinhardt, P. J. 1999, Science, 284, 1481\n\n%\\bibitem[Bahcall, Lubin, \\& Dorman 1995]{bld95}\n%Bahcall, N. A., Lubin, L. M., \\& ... |
astro-ph0002051 | The intragroup medium in loose groups of galaxies | [
{
"author": "School of Physics and Astronomy"
},
{
"author": "Edgbaston"
},
{
"author": "Birmingham B15 2TT"
},
{
"author": "UK"
}
] | \noindent We have used the {ROSAT} PSPC to study the properties of a sample of 24 X-ray bright galaxy groups, representing the largest sample examined in detail to date. Hot plasma models are fitted to the spectral data to derive temperatures, and modified King models are used to characterise the surface brightness pro... | [
{
"name": "loosegrp.tex",
"string": "\\documentstyle[general_cite,psfig]{mn}\n\\bibliographystyle{mnras}\n\\title{The intragroup medium in loose groups of galaxies}\n\\author[Stephen F. Helsdon and Trevor J. Ponman]\n {Stephen F. Helsdon\\thanks{E-mail: sfh@star.sr.bham.ac.uk} and Trevor J.\n Ponman ... | [
{
"name": "loosegrp.bbl",
"string": "\\begin{thebibliography}{Finoguenov \\& Ponman<1999>}\n\n\\bibitem[Allen \\& Fabian<1998>]{allen98}\nAllen~S.~W., Fabian~A.~C., 1998, MNRAS, 297, 57\n\n\\bibitem[Arnaud \\& Evrard<1999>]{arnaud99}\nArnaud~M., Evrard~A.~E., 1999, preprint, astro-ph/9806353\n\n\\bibitem[Ar... |
astro-ph0002052 | Relativistic Effects in the Pulse Profile of the 2.5 msec X-Ray Pulsar SAX~J1808.4-3658 | [
{
"author": "Eric C. Ford"
}
] | We analyze the properties of the pulsed emission from the accreting millisecond pulsar \saxpsr in observations of its April 1998 outburst by the Rossi X-Ray Timing Explorer. Pulse phase spectroscopy shows that the emission evolves from a hard spectrum (power law with photon index $2.39\pm0.06$) to a soft spectrum (inde... | [
{
"name": "ford1808.tex",
"string": "% Relativistic Effects in SAX J1808.4-3658\n% Eric C. Ford \n% submitted to ApJ, 2 February 2000\n% uses AAS preprint style sheets version 5.01\n\n% note this file uses BibTeX, citations defined in refs.bib\n\n\\documentclass[preprint2,11pt]{aastex}\n%\\documentclass{a... | [
{
"name": "astro-ph0002052.extracted_bib",
"string": "\\begin{thebibliography}{16}\n\\expandafter\\ifx\\csname natexlab\\endcsname\\relax\\def\\natexlab#1{#1}\\fi\n\n\\bibitem[{{Braje} {et~al.}(2000){Braje}, {Romani}, \\& {Rauch}}]{brr00}\n{Braje}, T., {Romani}, R., \\& {Rauch}, K. 2000, ApJ in press\n\n\\b... |
astro-ph0002053 | Black hole X-ray binaries:\\ A new view on soft-hard spectral transitions | [
{
"author": "F. Meyer \\inst{1}"
},
{
"author": "B.F. Liu \\inst{1}\\inst{,2}"
},
{
"author": "E. Meyer-Hofmeister \\inst{1}"
}
] | The theory of coronal evaporation predicts the formation of an inner hole in the cool thin accretion disk for mass accretion rates below a certain value ($\approx$ 1/50 of the Eddington mass accretion rate) and the sudden disappearance of this hole when the mass accretion rate rises above that value. The inner edge of ... | [
{
"name": "LBm102.tex",
"string": "\\documentclass{aa} % <-- \"class\" anstelle von \"style\"\n\\usepackage{amssymb,graphicx} % <-- \"graphicx\" fuer Bilder, \"amssymb\"\n\t\t\t % fuer einige besondere\n\t\t\t % mathematische Symbole\n\n\\sloppy\n\n\\begin{document}\n\n\\the... | [
{
"name": "astro-ph0002053.extracted_bib",
"string": "\\begin{thebibliography}\n{}\n\\bibitem{ref:5} Campana S., Colpi M., Mereghetti S., 1998, A\\&A\nRev. 8, 269\n\\bibitem{ref:10} Cui W., Zhang S.N., Focke W. et al., 1997, ApJ 484,383\n\\bibitem{ref:19} Esin A.A., McClintock J.E, Narayan R., 1997, ApJ 489... |
astro-ph0002054 | Thomson Thick X-ray Absorption in a Broad Absorption Line Quasar PG0946+301 | [
{
"author": "S. Mathur\\altaffilmark{1,2}"
},
{
"author": "P. J. Green\\altaffilmark{2}"
},
{
"author": "N. Arav\\altaffilmark{3}"
},
{
"author": "M. Brotherton\\altaffilmark{4}"
},
{
"author": "M. Crenshaw\\altaffilmark{5}"
},
{
"author": "M. deKool\\altaffilmark{6}"
}... | We present a deep ASCA observation of a Broad Absorption Line Quasar (BALQSO) PG0946+301. The source was clearly detected in one of the gas imaging spectrometers, but not in any other detector. If BALQSOs have intrinsic X-ray spectra similar to normal radio-quiet quasars, our observations imply that there is Thomson th... | [
{
"name": "astro-ph0002054.tex",
"string": "%%\n%% Beginning of file 'sample.tex'\n%%\n%% Modified 03 Nov 99\n%%\n%% This is a sample manuscript marked up using the\n%% AASTeX v5.0 LaTeX 2e macros.\n\n%% The first piece of markup in an AASTeX v5.0 document\n%% is the \\documentclass command. LaTeX will igno... | [
{
"name": "astro-ph0002054.extracted_bib",
"string": "\\begin{thebibliography} is followed by an empty set of\n%% curly braces. If you forget this, LaTeX will generate the error\n%% \"Perhaps a missing \\item?\".\n%%\n%% thebibliography produces citations in the text using \\bibitem-\\cite\n%% cross-refere... |
astro-ph0002055 | Gravitational waves from cosmological compact binaries | [
{
"author": "R. Schneider$^1$"
},
{
"author": "V. Ferrari$^1$"
},
{
"author": "S. Matarrese$^{2,3}$ and S. F. Portegies Zwart$^{4,5}$"
},
{
"author": "$^{1}$Dipartimento di Fisica ``G. Marconi\""
},
{
"author": "Universit\\'a degli Studi di Roma"
},
{
"author": "``La Sapi... | We consider gravitational waves emitted by various populations of compact binaries at cosmological distances. We use population synthesis models to characterize the properties of double neutron stars, double black holes and double white dwarf binaries as well as white dwarf-neutron star, white dwarf-black hole and blac... | [
{
"name": "final_binaries.tex",
"string": "\\documentstyle[psfig]{mn}\n\n\\newif\\ifAMStwofonts\n\\AMStwofontstrue\n\n%%%%% AUTHORS - PLACE YOUR OWN MACROS HERE %%%%%\n\\newcommand{\\be}{\\begin{equation}} % for lazy typers\n\\newcommand{\\ee}{\\end{equation}}\n\\newcommand{\\beq}{\\begin{eqnarray}}\n\\n... | [
{
"name": "astro-ph0002055.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\n\n\n\n\n\\bibitem{}\nAbt H.A., Levy S.G., 1978, ApJSS, 36, 241 \n\n\\bibitem{} \nBender P. L. \\& Hils D., 1997, Class. Quant. Gravity,\n14, 1439 \n\n\\bibitem{}\nBender P.L. for the LISA SCIENCE TEAM, 1998, {\\em LISA Pre... |
astro-ph0002056 | The Light Elements Be and B as Stellar Chronometers in the Early Galaxy | [
{
"author": "Timothy C. Beers"
}
] | Recent detailed simulations of Galactic Chemical Evolution have shown that the heavy elements, in particular [Fe/H], are expected to exhibit a weak, or absent, correlation with stellar ages in the early Galaxy due to the lack of efficient mixing of interstellar material enriched by individual Type II supernovae. A prom... | [
{
"name": "beers.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{Beers, Suzuki, \\& Yoshii}{The Light Elements as Chronometers}\n\\pagestyle{myheadings}\n\\nofiles\n\n% Some definitions I use in these instructions.\n\n\\def\\emphasize#1{{\\sl#1\\/}}\n\\def\\arg#1{{\\it#1\\/}... | [] |
astro-ph0002057 | The Warp of the Galaxy and the Orientation of the LMC Orbit | [
{
"author": "I. Garc\\'{\\i}a-Ruiz$^1$"
},
{
"author": "K. Kuijken$^1$"
},
{
"author": "J. Dubinski$^2$"
},
{
"author": "Postbus 800"
},
{
"author": "9700 AV Groningen"
},
{
"author": "The Netherlands"
},
{
"author": "$^2$Department of Astronomy and CITA"
},
{... | After studying the orientation of a warp generated by a companion satellite, we show that the Galactic Warp would be oriented in a different way if the Magellanic Clouds were its cause. We have treated the problem analytically, and complemented it with numerical N-Body simulations. | [
{
"name": "astro-ph.tex",
"string": "%\\documentstyle[11pt]{article}\n\n\\documentstyle{mn}\n\\newif\\ifAMStwofonts\n\\AMStwofontstrue\n\n%%%%% AUTHORS - PLACE YOUR OWN MACROS HERE %%%%%\n\n%\\newcommand{\\plotone}[1]{\\centerline{#1}}\n\\newcommand{\\plotone}[1]{\\epsfxsize=1.0\\hsize\\epsfbox{#1}}\n\\newc... | [
{
"name": "astro-ph0002057.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[\\protect\\citename{Barnes \\& Hut }1986]{bh86}\nBarnes, J., Hut, P., 1986, Nature, 324, 446\n\\bibitem[\\protect\\citename{Binney }1992]{b92}\nBinney, J., 1992, Annu. Rev. Astron. Astrophysics, 30, 51\n\\bibitem[\\p... |
astro-ph0002058 | Death of Stellar Baryonic Dark Matter | [
{
"author": "Katherine Freese\\inst{1}"
},
{
"author": "Brian Fields\\inst{2}"
},
{
"author": "David Graff\\inst{3}"
}
] | The nature of the dark matter in the haloes of galaxies is one of the outstanding questions in astrophysics. All stellar candidates, until recently thought to be likely baryonic contributions to the Halo of our Galaxy, are shown to be ruled out. Faint stars and brown dwarfs are found to constitute only a few percent of... | [
{
"name": "freese.tex",
"string": "\\documentclass{cl2emult}\n\n\\usepackage{makeidx} % allows index generation\n\\usepackage{graphicx} % standard LaTeX graphics tool\n % for including eps-figure files\n\\usepackage{subeqnar} % subnumbers individual equations\n % w... | [
{
"name": "astro-ph0002058.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\n\\bibitem{kfrbfgk} Bahcall, J.N., Flynn,. C., Gould, A.,\n\\& Kirkahos, S., 1994, ApJ, 435, L51\n\\bibitem{kfrgf96a} Graff, D.S., \\& Freese, K. 1996a, ApJ, 456, L49\n\\bibitem{kfrgf96b} Graff, D.S., \\& Freese, K. 1996b, ... |
astro-ph0002059 | Kinematics of Molecular Hydrogen Emission from Planetary and Pre-planetary Nebulae | [
{
"author": "Joel H. Kastner"
},
{
"author": "Ian Gatley"
}
] | We report results from a program of high-resolution spectral mapping of rotational H$_2$ emission from bipolar planetary and pre-planetary nebulae. Long-slit spectra obtained with the NOAO Phoenix near-infrared spectrometer allow us to probe the molecular kinematics of these nebulae at moderate spatial resolution. We f... | [
{
"name": "kastner1.tex",
"string": "\\documentstyle[11pt,newpasp,epsf,twoside]{article}\n\\markboth{Kastner, Gatley, \\& Weintraub}{H$_2$ Kinematics of PNs and PPNs}\n\\pagestyle{myheadings}\n%\\nofiles\n\n% Some definitions I use in these instructions.\n\n%\\def\\emphasize#1{{\\sl#1\\/}}\n%\\def\\arg#1{{\... | [] |
astro-ph0002060 | From Historical Perspectives to Some Modern Possibilities | [
{
"author": "Lawrence H. Aller"
}
] | A historical perspective on the study of asymmetries in planetary nebulae (PNs) is presented. We also describe our ongoing work in high resolution spectroscopy of planetaries, and discuss some likely future directions for the study of asymmetrical PNs. | [
{
"name": "Aller.tex",
"string": "\\documentstyle[11pt,newpasp,twoside]{article}\n\\markboth{Aller}{Historical Perspectives}\n\\pagestyle{myheadings}\n%\\nofiles\n\n% Some definitions I use in these instructions.\n\n%\\def\\emphasize#1{{\\sl#1\\/}}\n%\\def\\arg#1{{\\it#1\\/}}\n%\\let\\prog=\\arg\n\n%\\def\\... | [] |
astro-ph0002061 | [] | [
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"name": "sbmitted.tex",
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astro-ph0002062 | Stellar Iron Abundances at the Galactic Center | [
{
"author": "Solange V. Ram\\'{\\i}rez\\altaffilmark{1,2}"
},
{
"author": "K. Sellgren\\altaffilmark{1,2}"
}
] | We present measurements of [Fe/H] for six M supergiant stars and three giant stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star within 30 pc of the GC. The results are based on high-resolution ($\lambda / \Delta \lambda =$ 40,000) $K-$band spectra, taken with CSHELL at the NASA Infrared Telescope... | [
{
"name": "preprint.tex",
"string": "%This manuscript is prepared in AASTex 5.0 style\n\n\\documentclass[preprint,epsf]{aastex}\n\\input epsf\n\n\\newcommand{\\kms}{km~s$^{-1}$}\n\\newcommand{\\teff}{$T_{\\rm eff}$}\n\\newcommand{\\mbol}{$M_{\\rm bol}$}\n\\newcommand{\\aori}{$\\alpha$ Ori}\n\n\\received{Nov... | [
{
"name": "astro-ph0002062.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[Afflerbach et al.(1997)]{aff97} Afflerbach, A., Churchwell, E.,\n\\& Werner, M. W., 1997, \\apj, 478, 190\n\n\\bibitem[Audouze \\& Tinsley(1976)]{aud76} Audouze, J. \\& Tinsley, B. M. 1976, \n\\araa, 14, 43\n\n\\bi... |
astro-ph0002063 | STRUCTURE OF THE CIRCUMNUCLEAR REGION OF SEYFERT 2 GALAXIES REVEALED BY RXTE HARD X--RAY OBSERVATIONS OF NGC 4945 | [
{
"author": "G. Madejski$^{1,2}$"
},
{
"author": "P. \\.{Z}ycki$^{3}$"
},
{
"author": "C. Done$^{4}$"
},
{
"author": "A. Valinia$^{1,2}$"
},
{
"author": "P. Blanco$^{5}$"
},
{
"author": "R. Rothschild$^{5}$"
},
{
"author": "B. Turek$^{1,6}$"
}
] | NGC~4945 is one of the brightest Seyfert galaxies on the sky at 100 keV, but is completely absorbed below 10 keV, implying an optical depth of the absorber to electron scattering of a few; its absorption column is probably the largest which still allows a direct view of the nucleus at hard X--ray energies. Our observat... | [
{
"name": "4945_apJ_lanl.tex",
"string": "\\documentstyle[11pt,aaspp4]{article}\n\n\\newcommand {\\ie} {{\\it i.e.}}\n\\newcommand {\\cf} {{\\it cf.}}\n\n\\newcommand {\\eg} {{\\it e.g.}}\n\\newcommand {\\ea} {{\\it et~al.}}\n\n\\newcommand {\\be} {\\begin{equation}}\n\\newcommand {\\ee} {\\end{equation}}... | [] |
astro-ph0002064 | Correlation Statistics of Spectrally-Varying Quantized Noise | [
{
"author": "Carl R. Gwinn"
}
] | I calculate the noise in the measured correlation functions and spectra of digitized, noiselike signals. In the spectral domain, the signals are drawn from a Gaussian distribution with variance that depends on frequency. Nearly all astrophysical signals have noiselike statistics of this type, many with important spectr... | [
{
"name": "spect_57.tex",
"string": "% spect_54.tex\n% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n%\n%\n\\documentclass[10pt,preprint]{aastex}\n%\n\\def\\re{{\\rm Re}}\n\\def\\im{{\\rm Im}}\n%\n\\def\\gtwid{\\mathrel{\\raise.3ex\\hbox{$>$\\kern-.75em\\lower1ex\\hbox{$\\sim$}}}}\n\\def\\ltwid{\\mathrel{\\ra... | [
{
"name": "astro-ph0002064.extracted_bib",
"string": "\\begin{thebibliography}{99}\n% \\bibitem[Anantharamaiah et al.(1991)]{ana91}Anantharamaiah, K. R., Deshpande, A. A., Radhakrishnan, V., Ekers, R. D., Cornwell, T. J., \\& Goss, W. M. 1991, ASP Conf. Ser. 19: IAU Colloq. 131: Radio Interferometry. Theory... |
astro-ph0002065 | An X-ray Flare Detected on the M8 dwarf VB 10 | [
{
"author": "Thomas A. Fleming"
}
] | We have detected an X-ray flare on the very low mass star VB 10 (GL 752 B; M8 V) using the ROSAT High Resolution Imager. VB 10 is the latest type (lowest mass) main sequence star known to exhibit coronal activity. X-rays were detected from the star during a single 1.1-ksec segment of an observation which lasted 22 ksec... | [
{
"name": "ms.tex",
"string": "\\documentstyle[12pt,aaspp4]{article}\n%\\received{ }\n%\\accepted{ }\n%\\journalid{ }{ }\n%\\articleid{ }{ }\n\\begin{document}\n\\title{ An X-ray Flare Detected on the M8 dwarf VB 10 }\n\n\\author{ Thomas A. Fleming }\n\\affil{ Steward Observatory \\\\ \nUniversity of Arizon... | [] |
astro-ph0002066 | \hst\/ Images of Stephan's Quintet: Star Cluster Candidates in a Compact Group Environment | [
{
"author": "S. C. Gallagher"
}
] | We present \hst\/ WFPC2 images of Stephan's Quintet which encompass three interacting galaxies and their associated tidal features. These deep, three-color ($B,V,I$) images indicate recent, massive stellar system formation in various regions within the compact group environment. We have identified star cluster candidat... | [
{
"name": "gallaghers.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{Gallagher, Hunsberger, Charlton, \\& Zaritsky}{Star Cluster Candidates In Stephan's Quintet}\n\\pagestyle{myheadings}\n\\nofiles\n\n\n\\def\\emphasize#1{{\\sl#1\\/}}\n\\def\\arg#1{{\\it#1\\/}}\n\\let\\prog... | [] |
astro-ph0002067 | Fast Reconnection of Magnetic Fields in Turbulent Fluids | [] | Reconnection is the process by which magnetic fields in a conducting fluid change their topology. This process is essential for understanding a wide variety of astrophysical processes, including stellar and galactic dynamos and astrophysical turbulence. To account for solar flares, solar cycles and the structure of the... | [
{
"name": "proc.tex",
"string": "\\documentclass[proceedings]{rmaa}\n\n%% Miscellaneous definitions\n\\newcommand{\\ibid}{\\rule[-0.03cm]{4.7em}{.01cm}.\\ }\n\\newcommand{\\taulyc}{\\mbox{$\\tau_{LyC}$}}\n\\newcommand{\\alphaalpha}{\\mbox{$\\alpha^{eff}_{H\\alpha}$}}\n\\newcommand{\\alphaB}{\\mbox{$\\alpha_... | [
{
"name": "astro-ph0002067.extracted_bib",
"string": "\\begin{thebibliography}\n\\bibitem{BH98}Balbus, S. A., \\& Hawley, J. F. 1998, Rev. Mod. Phys., 1, 1 \n\\bibitem{BJ96} \nBarghouty, A. F., \\& Jokipii, J. R. 1996, \\apj, 470, 858\n\\bibitem{B84}Biskamp, D.\\ 1984, Phys. Lett. A, 105, 124\n\\bibitem{B86... |
astro-ph0002068 | The role of the outer boundary condition in accretion disk models: theory and application | [
{
"author": "Feng Yuan"
}
] | In a previous paper (Yuan 1999, hereafter Paper I), we find that the outer boundary conditions(OBCs) of an optically thin accretion flow play an important role in determining the structure of the flow. Here in this paper, we further investigate the influence of OBC on the dynamics and radiation of the accretion flow on... | [
{
"name": "fyuan.tex",
"string": "\\documentstyle[11pt,aaspp4,flushrt]{article} % this is for submittal (double-s\n%\\documentstyle[emulateapj]{article}\n\\def\\be{\\begin{equation}}\n\\def\\ee{\\end{equation}}\n\\def\\mdot{\\dot{m}}\n\\def\\ergs{{\\rm\\,erg\\,s^{-1}}}\n\\def\\msun{M_{\\odot}}\n\\def\\ergs... | [] |
astro-ph0002069 | [
{
"author": "Feng Yuan"
}
] | Taking optically thin accretion flows as an example, we investigate the dynamics and the emergent spectra of accretion flows with different outer boundary conditions (OBCs) and find that OBC plays an important role in accretion disk model. This is because the accretion equations describing the behavior of accretion flo... | [
{
"name": "fyuan.tex",
"string": "\\documentclass{edbk} % Computer Modern font calls\n\\usepackage[dvips]{epsfig}\n\\usepackage{edbkps}% PostScript font calls\n\n\\setcounter{secnumdepth}{3}\n\\setcounter{tocdepth}{1}\n\\kluwerbib\n\n\\def\\be{\\begin{equation}}\n\\def\\ee{\\end{equation}}\n\\def\\mdot{\\do... | [
{
"name": "astro-ph0002069.extracted_bib",
"string": "\\bibitem{}\nAbramowicz, M.A., et al. 1988, ApJ, 332, 646 \n\n\n\\bibitem{}\nAbramowicz, M., A., Zurek, W.H., 1981, ApJ, 246, 31\n\n\n\\bibitem{}\nChen, X., Abramowicz, M. A., \\& Lasota, J.-P. 1997, ApJ, 476, 61\n\n\n\\bibitem{}\nChen, X. \\& Taam, R. 1... | |
astro-ph0002070 | [] | \noindent{We present an overview of observational progress in the study of extragalactic globular cluster systems. Globular clusters turn out to be excellent tracers not only for the star-formation histories in galaxies, but also for kinematics at large galactocentric radii. Their properties can be used to efficiently ... | [
{
"name": "gcs_rev.tex",
"string": "% after proof corrections\n\\NeedsTeXFormat{LaTeX2e}\n\\documentclass[twoside]{article}\n\\usepackage[latin1]{inputenc}\n\\usepackage{t1enc}\n\\usepackage{a4}\n\\usepackage{tabularx}\n\\usepackage{epsf}\n\\usepackage{psfig}\n\\usepackage{rotate}\n\n\\textheight=194mm\n\\t... | [] | |
astro-ph0002071 | Alternative Solutions to Big Bang Nucleosynthesis | [
{
"author": "Hannu Kurki-Suonio"
}
] | Standard big bang nucleosynthesis (SBBN) has been remarkably successful, and it may well be the correct and sufficient account of what happened. However, interest in variations from the standard picture come from two sources: First, big bang nucleosynthesis can be used to constrain physics of the early universe. Second... | [
{
"name": "kurkisuonio.tex",
"string": "\\documentstyle[11pt,newpasp,twoside, epsf]{article}\n\\markboth{Kurki-Suonio}{Alternative Solutions to BBN}\n\\pagestyle{myheadings}\n\\nofiles\n\n% Some definitions I use in these instructions.\n\n\\def\\emphasize#1{{\\sl#1\\/}}\n\\def\\arg#1{{\\it#1\\/}}\n\\let\\pr... | [] |
astro-ph0002072 | VLBI differential astrometry at 43\,GHz | [
{
"author": "J.C.~Guirado\\inst{1}"
},
{
"author": "J.M.~Marcaide\\inst{1}"
},
{
"author": "M.A.~P\\'erez-Torres\\inst{1}"
},
{
"author": "E.~Ros\\inst{2}"
}
] | From 43\,GHz VLBA observations of the pair of radio sources \1928+738 and \2007+777 we have demonstrated the feasibility of precision phase-delay differential astrometric techniques at millimeter wavelengths. For a pair of sources with 5\degr\, separation and high antenna elevations, we have shown that present astromet... | [
{
"name": "guirado.tex",
"string": "%\\documentclass[referee]{aa}\n\\documentclass{aa}\n\\def\\et{et al.\\ } \n\\def\\1928+738{QSO\\,1928+738} \n\\def\\2007+777{BL\\,2007+777} \n\\addtolength{\\topmargin}{1 cm} \n\\begin{document}\n\n\\thesaurus{11(05.01.1; 03.20.2; 11.17.4 \\1928+738... | [
{
"name": "astro-ph0002072.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[]{}\nBeasley A.J., Conway J.E., 1995, In: Zensus J.A., Diamond P.J., Napier P.J. (eds.), \nVery Long Baseline Interferometry and the VLBA, ASP Conference Series 82, \nSan Francisco, CA, USA, p.\\ 327\n\n\\bibitem[]... |
astro-ph0002073 | The Morphological and Structural Classification of Planetary Nebulae | [
{
"author": "Arturo Manchado"
}
] | We present a statistical analysis of a complete sample (255) of northern planetary nebulae (PNe). Our analysis is based on morphology as a main parameter. The major morphological classes are: round (26\% of the sample), elliptical (61 \%), and bipolar (13 \%) PNe. About a half of the round and 30 \% of the elliptical P... | [
{
"name": "paperII.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{Manchado et al.}{The Morphological and Structural\nClassification of PNe}\n%\\author{Arturo Manchado}\n\\pagestyle{myheadings}\n\\nofiles\n\n% Some definitions I use in these instructions.\n\n \\def\\emphasiz... | [] |
astro-ph0002074 | Simultaneous Measurements of X-Ray Luminosity and Kilohertz Quasi-Periodic Oscillations in Low-Mass X-Ray Binaries | [
{
"author": "Eric C. Ford\\altaffilmark{1}"
},
{
"author": "Michiel van der Klis\\altaffilmark{1}"
},
{
"author": "Mariano \\mm\\altaffilmark{1,2}"
},
{
"author": "Rudy Wijnands\\altaffilmark{1,3}"
},
{
"author": "Jeroen Homan\\altaffilmark{1}"
},
{
"author": "Peter G. Jo... | We measure simultaneously the properties of the energy spectra and the frequencies of the kilohertz quasi-periodic oscillations (QPOs) in fifteen low mass X-ray binaries covering a wide range of X-ray luminosities. In each source the QPO frequencies cover the same range of approximately $300$ Hz to $1300$ Hz, though th... | [
{
"name": "fordqpos.tex",
"string": "% Summary paper of QPOs - spectral fits + frequencies for all sources\n% Ford et al., accepted by ApJ 2 February 2000\n% uses AAS preprint style sheets version 5.01\n% draft1: 20 August 1999\n\n% note this file uses BibTeX, citations defined in refs.bib\n\n\\documentcl... | [
{
"name": "astro-ph0002074.extracted_bib",
"string": "\\begin{thebibliography}{77}\n\\expandafter\\ifx\\csname natexlab\\endcsname\\relax\\def\\natexlab#1{#1}\\fi\n\n\\bibitem[{Alpar \\& Shaham(1985)}]{as85}\nAlpar, M. \\& Shaham, J. 1985, Nature, 316, 239\n\n\\bibitem[{{Barret} \\& {Grindlay}(1995)}]{bg95}... |
astro-ph0002075 | On energy spectra of UHE cosmic rays accelerated in supergalactic accretion flows | [
{
"author": "G. Siemieniec-Ozi\\c{e}b{\\l}o"
},
{
"author": "M. Ostrowski"
}
] | Some ultra-high energy (UHE) cosmic ray (CR) events may be correlated with the Local Supercluster plane. We consider acceleration of such particles at the large-scale accretion flows of matter towards such plane and/or accretion flows onto galaxy clusters. The formed shocks and the general compression flow are expected... | [
{
"name": "ms8663.tex",
"string": "\\input{epsfig.sty}\n\\documentstyle{l-aa} \n%\\documentstyle[12pt]{article}\n%\\documentstyle[referee]{l-aa}\n\\newcommand{\\be}{\\begin{equation}}\n\\newcommand{\\ee}{\\end{equation}}\n\\newcommand{\\bea}{\\begin{eqnarray}}\n\\newcommand{\\eea}{\\end{eqnarray}}\n\n\\be... | [] |
astro-ph0002076 | [] | [
{
"name": "gsum.tex",
"string": "\\begin{table}[h]\n\\def\\arraystretch{1.2}\n\\centering\n\\begin{tabular}{ll}\n \n\\hline\n$I(10^5<N_e<1.15\\cdot10^6)$ & $(8.95\\pm 0.18)\\cdot10^{-11}(N_e/10^5)^{\\gamma_1}$\\\\\n$I(N_e>2.56\\cdot10^6)$ & $(3.23\\pm 0.40)\\cdot10^{-13}(N_e/10^6)^{\\gam... | [
{
"name": "astro-ph0002076.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\\renewcommand{\\baselinestretch}{0.1}\n\\parskip0.ex\n%\n\\bibitem{hayakawa}\nS. Hayakawa, {\\it Cosmic Ray Physics}, Interscience Monographs and \nTexts in Physics and Astronomy, V. 22, Wiley-Interscience, 1969\n\\bibitem{... | ||
astro-ph0002077 | [] | [
{
"name": "paper.tex",
"string": "\\documentclass[11pt,dvips]{article}\n\\usepackage{epsfig}\n\\usepackage{wrapfig}\n% Setting various length parameters (DO NOT ALTER):\n\\setlength{\\textheight}{9in}\n\\setlength{\\textwidth}{6.63in}\n\\setlength{\\hoffset}{-0.2in}\n\\setlength{\\voffset}{0.37in}\n\\setle... | [
{
"name": "astro-ph0002077.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\\renewcommand{\\baselinestretch}{0.1}\n\\parskip0.ex\n\\bibitem{AH-miayke}\nS. Miayke et al., Proc. 16$^{th}$ ICRC (Kyoto) {\\bf 13} (1979) 171\\\\\nS. Miayke et al., Proc. 17$^{th}$ ICRC (Paris) {\\bf 11} (1981) 293\\\\\nB... | ||
astro-ph0002078 | NICMOS Narrow-band Infrared Photometry of TW Hya Association Stars | [
{
"author": "David A. Weintraub\\altaffilmark{1}"
},
{
"author": "Didier Saumon\\altaffilmark{1}"
},
{
"author": "Joel H. Kastner\\altaffilmark{2}"
},
{
"author": "and Thierry Forveille\\altaffilmark{3}"
}
] | We have obtained 1.64, 1.90 and 2.15 $\mu$m narrow-band images of five T Tauri stars in the TW Hya Association (TWA) using the Near-Infrared Camera and Multiobject Spectrometer aboard the {Hubble Space Telescope}. Most of the T Tauri stars in our study show evidence of absorption by H$_2$O vapor in their atmospheres; i... | [
{
"name": "re_revised.tex",
"string": "\\documentstyle[12pt,aasms4]{article}\n%\\documentstyle[12pt,epsf,/nfs/yohoia/h1/jhk/tex/aastex40/aasms4]{article}\n%\\documentstyle[12pt,/home/david/tex/aastex/aasms4]{article}\n\n\n%\\received{today}\n%\\accepted{tomorrow}\n%\\slugcomment{Version date: October 1, 199... | [
{
"name": "astro-ph0002078.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[Allard et al.\\ 1997]{alla1997}\nAllard, F., Hauschildt, P. H., Alexander, D. R., \\& Starrfield, S. 1997,\nARAA, 35, 137\n\n\\bibitem[Allard et al.\\ 1996]{alla1996}\nAllard, F. Hauschildt, P. H., Baraffe, I. \\& Ch... |
astro-ph0002079 | Pinpointing the Position of the Post-AGB Star at the Core of RAFGL 2688 using Polarimetric Imaging with NICMOS | [
{
"author": "David A. Weintraub\\altaffilmark{1}"
},
{
"author": "Joel H. Kastner\\altaffilmark{2}"
},
{
"author": "Dean C. Hines\\altaffilmark{3}"
},
{
"author": "Raghvendra Sahai\\altaffilmark{4}"
}
] | We have used infrared polarimetric imaging with NICMOS to determine precisely the position of the star that illuminates (and presumably generated) the bipolar, pre-planetary reflection nebula RAFGL 2688 (the Egg Nebula). The polarimetric data pinpoint the illuminating star, which is not detected directly at wavelengths... | [
{
"name": "ms_revised.tex",
"string": "\\documentstyle[12pt,aasms4]{article}\n%\\documentstyle[12pt,/home/david/tex/aastex/aasms4]{article}\n%\\documentstyle[12pt,/nfs/yohoia/h1/jhk/tex/aastex40/aasms4]{article}\n\n% Here's some slug-line data. The receipt and acceptance dates will be \n% filled in by the ... | [
{
"name": "astro-ph0002079.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n%\\bibitem[Cohen \\& Kuhi 1977]{cohe1977}\n% Cohen, M. \\& Kuhi, L. V.1977, \\apj, 213, 79.\n\n%\\bibitem[Cox et al.\\ 1997]{cox1997}\n% Cox, P., Maillard, J.-P., Huggins, P. J., Forveille, T., Simons, D.,\n% ... |
astro-ph0002080 | Nearby Gas-Rich Low Surface Brightness Galaxies | [
{
"author": "Stephen E. Schneider"
}
] | We examine the Fisher--Tully $cz<1000$ km s$^{-1}$ galaxy sample to determine whether it is a complete and representative sample of {all} galaxy types, including low surface brightness populations, as has been recently claimed. We find that the sample is progressively more incomplete for galaxies with (1) smaller physi... | [
{
"name": "ms.tex",
"string": "\\documentstyle[aaspp4]{article}\n \n%\\received{ }\n%\\accepted{ }\n%\\journalid{ }{ }\n%\\articleid{ }{ }\n \n%\\slugcomment{ }\n \n \n\\lefthead{Schneider \\& Schombert}\n\\righthead{Nearby LSB Galaxies}\n \n\\begin{document}\n \n\\title{Nearby Gas-Rich Low Surface Brightne... | [
{
"name": "astro-ph0002080.extracted_bib",
"string": "\\begin{thebibliography}{}\n \n\\bibitem{}\nBothun, G. D., Impey, C. D., Malin, D. F., Mould, J. R. 1987, AJ, 94, 23\n\n\\bibitem{}\nBothun, G. D., Schombert, J. M., Impey, C. D., \\& Schneider, S. E. 1990, ApJ, 360, 427\n\n\\bibitem{}\nBriggs, F. H. 199... |
astro-ph0002081 | The Contribution of Faint Blue Galaxies to the Sub-mm Counts and Background | [
{
"author": "Geoff S. Busswell"
},
{
"author": "Tom Shanks"
},
{
"author": "Department of Physics"
},
{
"author": "Science Labs"
},
{
"author": "South Road"
},
{
"author": "Durham DH1 3LE"
},
{
"author": "UK"
}
] | Observations in the submillimetre waveband have recently revealed a new population of luminous, sub-mm sources. These are proposed to lie at high redshift and to be optically faint due to their high intrinsic dust obscuration. The presence of dust has been previously invoked in optical galaxy count models which assume ... | [
{
"name": "mypaper.tex",
"string": "%\\documentstyle[draft,epsf]{mn}\n\\documentstyle[graphicx]{mn}\n%\\usepackage{graphicx}\n%\\input{epsf}\n%\\usepackage{graphicx}\n\n%Define some symbols for fun...\n\\def\\hi{{\\rm H\\,{\\sc i} }}\n\\def\\hii{{\\rm H\\,{\\sc ii} }}\n\n%-----------------------------------... | [
{
"name": "astro-ph0002081.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[\\protect\\citename{Allen \\ }1995]{allen95}\nAllen, C.W. 1995, Astrophysical Quantities, pg. 197\n\n\\bibitem[\\protect\\citename{Alton et al.\\ }1998a]{alton98a}\nAlton, P.B. et al., 1998a, A\\&A, 335, 807A\n\n\\... |
astro-ph0002082 | The entropy and energy of intergalactic gas in galaxy clusters | [
{
"author": "E. J. Lloyd-Davies"
},
{
"author": "School of Physics and Astronomy"
},
{
"author": "Edgbaston"
},
{
"author": "Birmingham B15 2TT"
},
{
"author": "UK"
}
] | Studies of the X-ray surface brightness profiles of clusters, coupled with theoretical considerations, suggest that the breaking of self-similarity in the hot gas results from an `entropy floor', established by some heating process, which affects the structure of the intracluster gas strongly in lower mass systems. By ... | [
{
"name": "entropy.tex",
"string": "\\documentstyle[general_cite,psfig]{mn}\n\\bibliographystyle{mnras}\n\\title{The entropy and energy of intergalactic gas in galaxy\nclusters}\n\\author[E. J. Lloyd-Davies et al.]\n {E. J. Lloyd-Davies,\\thanks{E-mail: eld@star.sr.bham.ac.uk} \n T. J. Ponman a... | [
{
"name": "entropy.bbl",
"string": "\\begin{thebibliography}{Tenorio-Tagle \\& Mu\\~{n}oz Tu\\~{n}\\'{o}n<1997>}\n\n\\bibitem[Allen \\& Fabian<1998>]{allen98a}\nAllen~S.~W., Fabian~A.~C., 1998, MNRAS, 297, L57\n\n\\bibitem[Arnaud \\& Evrard<1999>]{arnaud98a}\nArnaud~M., Evrard~A.~E., 1999, MNRAS, 305, 631\n... |
astro-ph0002083 | A submillimetre survey of the star-formation history of radio galaxies | [
{
"author": "J. S. Dunlop$^{2}$"
},
{
"author": "D. H. Hughes$^{2,3}$"
},
{
"author": "S. Rawlings$^{4}$"
},
{
"author": "S. A. Eales$^{5}$"
},
{
"author": "and R. J. Ivison$^{6}$"
},
{
"author": "$^{1}$Joint Astronomy Centre"
},
{
"author": "660 N. A`oh\\={o}k\\=... | We present the results of the first major systematic submillimetre survey of radio galaxies spanning the redshift range $1 < z < 5$. The primary aim of this work is to elucidate the star-formation history of this sub-class of elliptical galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the JCM... | [
{
"name": "mnpaper.tex",
"string": "\\documentstyle[amssymb,epic,epsfig,multirow,pifont]{mn}\n\n\\newif\\ifAMStwofonts\n\n%%%%% AUTHORS - PLACE YOUR OWN MACROS HERE %%%%%\n\n\\def\\fig#1{Figure~\\ref{#1}}\n\\def\\Fig#1{Figure~\\ref{#1}}\n\\def\\Tab#1{Table~\\ref{#1}}\n\\def\\tab#1{Table~\\ref{#1}}\n\\def\\s... | [
{
"name": "astro-ph0002083.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[\\protect\\citename{{Akujor} et~al.{\\ }}{1991}]{asz91}\n{Akujor}~C.~E., {Spencer}~R.~E., {Zhang}~F.~J., {Davis}~R.~J., {Browne}~I.\n W.~A., {Fanti}~C., 1991, \\mnras, 250, 215, (ASZ91)\n\n\\bibitem[\\prot... |
astro-ph0002084 | X-Ray Spectral and Timing Evolution During the Decay of the 1998 Outburst from the Recurrent X-Ray Transient 4U~1630--47 | [] | We report on the X-ray spectral and timing behavior of the recurrent X-ray transient 4U~1630--47 for 51 RXTE observations made during the decay of its 1998 outburst. The observations began when the source was still relatively bright, and, during one of the early observations, a QPO with a non-Lorentzian profile occurre... | [
{
"name": "x1630.tex",
"string": "\n\\documentclass[letterpaper]{article}\n\n\\usepackage{emulateapj}\n\\usepackage{onecolfloat}\n\\usepackage{apjfonts}\n\\usepackage{amsmath}\n\\usepackage{graphicx}\n\n%\\textheight=24.4cm\n\\textheight=23.2cm\n\n\\begin{document}\n\n\\submitted{To Appear in the Astrophysi... | [
{
"name": "astro-ph0002084.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[Augusteijn, Kuulkers \\& Shaham 1993]{aks93} Augusteijn, T., Kuulkers, E. \\& \n\tShaham, J.~1993, A\\&A 279, L13\n\n\\bibitem[Belloni et al.~1997]{belloni97} Belloni, T. et al.~1997, A\\&A 322, 857\n\n\\bibitem[Br... |
astro-ph0002085 | [] | Naturally occurring water vapor maser emission at 1.35 cm wavelength provides an accurate probe for the study of accretion disks around highly compact objects, thought to be black holes, in the centers of active galaxies. Because of the exceptionally fine angular resolution, 200 microarcseconds, obtainable with very lo... | [
{
"name": "india-jmm.tex",
"string": "%\\documentstyle[12pt, aasms4]{article}\n\\documentstyle[11pt,aaspp4]{article}\n%\\documentstyle[11pt]{article}\n\\pagestyle{plain}\n\n\\renewcommand{\\topfraction}{.99}\n\\renewcommand{\\bottomfraction}{.99}\n\\renewcommand{\\textfraction}{.01}\n\n\n\n\\def\\plotfiddle... | [] | |
astro-ph0002086 | BINDING ENERGY AND THE FUNDAMENTAL PLANE OF GLOBULAR CLUSTERS | [
{
"author": "Dean E. McLaughlin\\altaffilmark{1}"
}
] | A physical description of the fundamental plane of Galactic globular clusters is developed which explains all empirical trends and correlations in a large number of cluster observables and provides a small but complete set of truly independent constraints on theories of cluster formation and evolution in the Milky Way.... | [
{
"name": "dempa.tex",
"string": "\\documentstyle[11pt,aaspp4,epsf]{article}\n\n\\begin{document}\n\n\\title{BINDING ENERGY AND THE FUNDAMENTAL PLANE OF GLOBULAR CLUSTERS}\n\\author{Dean E. McLaughlin\\altaffilmark{1}}\n\\affil{Department of Astronomy, 601 Campbell Hall\\\\\nUniversity of California, Berkel... | [] |
astro-ph0002087 | The Formation History of Globular Clusters | [
{
"author": "Dean E. McLaughlin\\inst{1,2}"
}
] | The properties of old globular cluster systems in galaxy halos are used to infer quantitative constraints on aspects of star formation that are arguably as relevant in a present-day context as they were during the protogalactic epoch. First, the spatial distribution of globulars in three large galaxies, together with t... | [
{
"name": "dempb.tex",
"string": "%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n%\n% sample.tex -- ESLAB Conference Proceedings tutorial paper\n% ----------------------------------------------------------\n% Lines starting with \"%\" are comments; they will be ignored... | [
{
"name": "astro-ph0002087.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[\\protect\\astroncite{Aguilar et al.}{1988}]{agu88}\nAguilar, L., Hut, P., \\& Ostriker, J. P. 1988, ApJ, 335, 720\n\n\\bibitem[\\protect\\astroncite{Ashman \\& Zepf}{1992}]{ash92}\nAshman, K. M., \\& Zepf, S. E. 1... |
astro-ph0002088 | Constraints on Cluster Formation from Old Globular Cluster Systems | [
{
"author": "Dean E. McLaughlin\\altaffilmark{1}"
}
] | The properties of old globular cluster systems (GCSs) in galaxy halos offer unique insight into the physical processes that conspire to form any generic star cluster, at any epoch. Presented here is a summary of the information obtained from (1) the specific frequencies (total populations) and spatial structures (densi... | [
{
"name": "dempc.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{McLaughlin}\n{Constraints on Cluster Formation from Globular Clusters}\n\\pagestyle{myheadings}\n\n\\begin{document}\n\n\\title{Constraints on Cluster Formation from Old Globular Cluster Systems}\n\n\\author{De... | [] |
astro-ph0002089 | Relic Neutrinos and Z-Resonance Mechanism for Highest-Energy Cosmic Rays | [
{
"author": "James L. Crooks"
},
{
"author": "James O. Dunn and Paul H. Frampton"
}
] | The origin of the highest-energy cosmic rays remains elusive. The decay of a superheavy particle (X) into an ultra-energetic neutrino which scatters from a relic (anti-)neutrino at the Z-resonance has attractive features. Given the necessary X mass of $10^{14\sim15}$ GeV, the required lifetime, $10^{15\sim16}$ y, rende... | [
{
"name": "AUGER2.tex",
"string": "\\documentstyle[preprint,aps]{revtex}\n\n\\begin{document}\n\n\\newcommand{\\be}{\\begin{equation}}\n\\newcommand{\\ee}{\\end{equation}}\n\\newcommand{\\bea}{\\begin{eqnarray}}\n\\newcommand{\\eea}{\\end{eqnarray}}\n\\newcommand{\\ba}{\\begin{array}}\n\\newcommand{\\ea}{\\... | [
{
"name": "astro-ph0002089.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\\bibitem{FKN}\nP.H. Frampton, B. Keszthelyi and Y.J. Ng, \nInt. J. Mod. Phys. {\\bf D8,} 117 (1999).\n\\bibitem{Greisen} \nK. Greisen, Phys. Rev. Lett. {\\bf 16,} 748 (1966);\n\\bibitem{KZ}\nG.T. Zatsepon and V.A. Kuzmin, P... |
astro-ph0002090 | Measuring the Size of the Vela Pulsar's Radio Emission Region | [
{
"author": "C.R. Gwinn"
}
] | We describe the expected distribution of intensity for a scintillating source of finite size observed through a scattering medium, including systematic and instrumental effects. We describe measurements of the size of the Vela pulsar, using this technique. | [
{
"name": "iau177.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{Gwinn et al.}{Vela Size}\n\\pagestyle{myheadings}\n\\nofiles\n\n% Some definitions I use in these instructions.\n\n\\def\\emphasize#1{{\\sl#1\\/}}\n\\def\\arg#1{{\\it#1\\/}}\n\\let\\prog=\\arg\n\n\\def\\edcomm... | [] |
astro-ph0002091 | Current cosmological constraints from a 10 parameter CMB analysis | [
{
"author": "\\Huge SOME PERMUTATION OF:"
}
] | We compute the constraints on a ``standard'' 10 parameter cold dark matter (CDM) model from the most recent CMB data and other observations, exploring 30 million discrete models and two continuous parameters. Our parameters are the densities of CDM, baryons, neutrinos, vacuum energy and curvature, the reionization opti... | [
{
"name": "10par.tex",
"string": "%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n% 000404\n%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n% THIS STUFF IS FOR MY FULLY PORTABLE REFERENCE NOTATION.\n\n\n%%%%%%%%%%%%%%%%%%%%%%%%%%%%%... | [
{
"name": "astro-ph0002091.extracted_bib",
"string": "\\bibitem{Jungman}\n\\rf\\nn Jungman G, \\nn Kamionkowski M, \\nn Kosowsky A\\multiand \n\\nnn Spergel D N;1996;Phys. Rev. D;54;1332\n% preprint astro-ph/9512139.\n% JUNGMAN G; KAMIONKOWSKI M; KOSOWSKY A; SPERGEL DN.\n% COSMOLOGICAL-PARAMETER DETERMINATI... |
astro-ph0002092 | Fragmentation Instability of Molecular Clouds: Numerical Simulations\altaffilmark{1} | [
{
"author": "R\\'{e}my Indebetouw\\altaffilmark{2}"
}
] | We simulate fragmentation and gravitational collapse of cold, magnetized molecular clouds. We explore the nonlinear development of an instability mediated by ambipolar diffusion, in which the collapse rate is intermediate to fast gravitational collapse and slow quasistatic collapse. Initially uniform stable clouds frag... | [
{
"name": "pp.tex",
"string": "\\documentclass[preprint2,eqsecnum]{aastex}\n\\usepackage{amssymb,amsbsy,graphics}\n\n\\begin{document}\n\\newlength{\\colw}\n\\setlength{\\colw}{3.2in}\n\n\\title{Fragmentation Instability of Molecular Clouds: \nNumerical Simulations\\altaffilmark{1}}\n\\author{R\\'{e}my Inde... | [
{
"name": "astro-ph0002092.extracted_bib",
"string": "\\begin{thebibliography}{}\n\\bibitem[Basu \\& Mouschovias(1994)]{bm94}Basu, S., \\& Mouschovias, T. Ch . \n1994, \\apj, 432, 720.\n%\n\\bibitem[Basu \\& Mouschovias(1995)]{bm95} Basu, S. \\& Mouschovias, T. Ch. \n1995, \\apj, 453, 271.\n%\n\\bibitem[B... |
astro-ph0002093 | Numerical simulation of accretion discs in close binary systems and discovery of spiral shocks | [] | The history of hydrodynamic numerical simulations for accretion disks in close binary systems is reviewed, in which emphasis is placed, in particular, on the facts that spiral shock waves were numerically found in 1986 by researchers including one of the present authors and that spiral structure was discovered in IP Pe... | [
{
"name": "xxxbarmat.tex",
"string": "\\documentclass[epsf]{kluwer}\n\\usepackage{epsfig}\n\\begin{document}\n\\begin{article}\n\\begin{opening}\n\\title{Numerical simulation of accretion discs in close binary systems and\ndiscovery of spiral shocks}\n\\author{Takuya \\surname{Matsuda} \\email{tmatsuda@kobe... | [
{
"name": "astro-ph0002093.extracted_bib",
"string": "\\begin{thebibliography}{99}\n\\bibitem[]{ba83}\nBath G.T., Edwards A.C., Mantle V.J., 1983, MNRAS, 205, 171\n\\bibitem[]{ba91}\nBalbus S. A., Hawley J. F., 1991, ApJ, 376, 214\n\\bibitem[]{ba96}\nBalbus S. A., Hawley J. F., Stone J. M., 1996, ApJ, 467, ... |
astro-ph0002094 | Water Ice in 2060 Chiron and its Implications for Centaurs and Kuiper Belt Objects | [
{
"author": "Jane X. Luu"
}
] | We report the detection of water ice in the Centaur 2060 Chiron, based on near-infrared spectra (1.0 - 2.5 $\micron$) taken with the 3.8-meter United Kingdom Infrared Telescope (UKIRT) and the 10-meter Keck Telescope. The appearance of this ice is correlated with the recent decline in Chiron's cometary activity: the de... | [
{
"name": "paper.tex",
"string": "\\documentclass[aasms,tighten,psfig,graphicx,11pt,a4]{aastex}\n\\slugcomment{Submitted to {\\it Ap. J. Letters}, accepted 31 Jan 2000}\n\n\\begin{document}\n\n\\title{Water Ice in 2060 Chiron and its Implications for Centaurs\nand Kuiper Belt Objects}\n\\author{Jane X. Luu}... | [] |
astro-ph0002095 | The CDS information hub | [
{
"author": "Fran\\c{c}oise Genova"
},
{
"author": "Daniel Egret"
},
{
"author": "Olivier Bienaym\\'e"
},
{
"author": "Fran\\c{c}ois Bonnarel"
},
{
"author": "Pascal Dubois"
},
{
"author": "Pierre Fernique"
},
{
"author": "G\\'erard Jasniewicz\\thanks{Groupe de Re... | The {Centre de Donn\'ees astronomiques de Strasbourg} (CDS) provides homogeneous access to heterogeneous information of various origins: information about astronomical objects in {\sc Simbad}; catalogs and observation logs in {\sc VizieR} and in the catalogue service; reference images and overlays in {\sc Aladin}; nome... | [
{
"name": "cdsaa99.tex",
"string": "%\\documentclass[referee]{aa}\n\\documentclass{aa}\n\\usepackage{graphics}\n%\\usepackage{times}\n\\hyphenation{data-base}\n\\begin{document}\n\n\\thesaurus{?? (04.01.1; 04.03.1; 01.16.1; 04.19.1; 01.19.2)}\n\n\\title{The CDS information hub}\n\n\\subtitle{On--line servic... | [
{
"name": "astro-ph0002095.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[2000]{aladin}\nBonnarel, F., Fernique, P., Bienaym\\'e, O., et al., 2000,\nA\\&AS, this issue\n\n\\bibitem[1998]{urania}\nBoyce, P.B., 1998, in {\\it LISA III}, eds.\\ U. Grothkopf,, H. Andernach, \nS. Stevens-Rayb... |
astro-ph0002096 | The Broad Line Region in Active Galactic Nuclei | [
{
"author": "D. Dultzin-Hacyan\\altaffilmark{1}"
},
{
"author": "P. Marziani\\altaffilmark{2}"
},
{
"author": "J.W. Sulentic\\altaffilmark{3}"
}
] | We review constraints on models of the broad line region that are imposed by observations of the emission lines in Active Galactic Nuclei. Comparison of high and low ionization lines in sources with FWHM H$\beta\leq$4000 km s$^{-1}$ points toward low ionization line emission produced in a flattened geometry (the accret... | [
{
"name": "dd_submitted.tex",
"string": "%%% Sample proceedings article for rmaa.cls\n%%%\n%%% Converted to RMAA(SC) style and annotated by Will Henney\n%%% (04 Oct1999)\n%% This file contains examples of many of the commands in the LaTeX\n%% document class rmaa.cls, such as the commands for specifying data... | [
{
"name": "astro-ph0002096.extracted_bib",
"string": "\\begin{thebibliography}{}\n%\\bibitem[Aretxaga et al.<1999>]{arex} Aretxaga, I., Joguet, B., Kunth, D., Melnick, J. \\& Terlevich, R. J. 1999, \\apjl, 519, L123\n\\bibitem[Abramowicz et al.<1988>]{abram88} Abramowicz M., Czerny B., Lasota J. P., Szuszk... |
astro-ph0002097 | A phase-reference study of the quasar pair 1038+528A,B | [
{
"author": "Mar\\'{\\i}a J. Rioja \\inst{1} \\inst{2}"
},
{
"author": "Richard W. Porcas\\inst{3} % \\fnmsep\\thanks{Just to show the usage % of the elements in the author field}"
}
] | We present results from $\lambda$ 3.6~cm observations of the quasar pair \object{1038+528} A and B, made in 1995 using the VLBA together with the Effelsberg 100m telescope. We describe the use of a phase-referencing technique to measure the astrometric separation between the quasars. We also introduce a new data analys... | [
{
"name": "rioja_17jan2000.tex",
"string": "% aa.dem\n% AA vers. 4.01, LaTeX class for Astronomy & Astrophysics\n% demonstration file\n% (c) Springer-Verlag HD\n%----------------------------------... | [
{
"name": "astro-ph0002097.extracted_bib",
"string": "\\begin{thebibliography}{}\n\n\\bibitem[1988]{alef88} Alef W.A., 1988, in Proc. IAU Symp. 129, \ned. Reid M., Moran J., Kluwer, p. \\ 523 \n\n\\bibitem[1995]{beasley95} Beasley A.J., Conway J.E., 1995, \nVery Long Baseline Interferometry and the VLBA, e... |
astro-ph0002098 | Chemistry in the Envelopes around Massive Young Stars | [
{
"author": "Ewine F.\\ van Dishoeck and Floris F.S.\\ van der Tak"
}
] | Recent observational studies of intermediate- and high-mass star-forming regions at submillimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components associated with young stellar objects are summarized. Procedures for determining the temperature, density and abundance p... | [
{
"name": "dishoeck.tex",
"string": "% SAMPLE1.TEX -- WGAS sample paper with minimal markup.\n\n% Lines starting with \"%\" are comments; they will be ignored by LaTeX.\n\n\\documentstyle[11pt,newpasp,psfig,epsf,twoside]{article}\n\\def\\gtsim{{_>\\atop{^\\sim}}}\n\\def\\ltsim{{_<\\atop{^\\sim}}}\n\n\\begin... | [] |
astro-ph0002099 | Geodetic Precession and the Binary Pulsar B1913+16 | [
{
"author": "A. Karastergiou"
},
{
"author": "M. Kramer"
},
{
"author": "N. Wex"
},
{
"author": "A. von Hoensbroech"
}
] | A change of the component separation in the profiles of the binary pulsar PSR B1913+16 has been observed for the first time (Kramer 1998) as expected by geodetic precession. In this work we extend the previous work by accounting for recent data from the Effelsberg 100-m telescope and Arecibo Observatory and testing mod... | [
{
"name": "contrib1.tex",
"string": "\\documentstyle[11pt,newpasp,twoside,epsf]{article}\n\\markboth{Karastergiou, Kramer, Wex \\& von Hoensbroech}\n{Geodetic Precession and the Binary Pulsar B1913+16}\n\\pagestyle{myheadings}\n\\nofiles\n\n\\begin{document}\n\\title{Geodetic Precession and the Binary Pulsa... | [] |
astro-ph0002100 | Reionization of the Universe and the Photoevaporation of Cosmological Minihalos | [
{
"author": "Alejandro C. Raga \\affil{Instituto de Astronom\\'{\\i}a, Universidad Nacional Aut\\'onoma de M\\'exico}"
}
] | The first sources of ionizing radiation to condense out of the dark and neutral IGM sent ionization fronts sweeping outward through their surroundings, overtaking other condensed objects and photoevaporating them. This feedback effect of universal reionization on cosmic structure formation is demonstrated here for the ... | [
{
"name": "shapiro.tex",
"string": "\\documentclass[proceedings]{rmaa}\n%%\n%% The file `rmaa.cls' should be somewhere in your TeX search path\n%% (e.g, in the current directory, or in a personal or system-wide\n%% directory of LaTeX packages. \n%%\n%% This will not work with old versions of LaTeX: any ver... | [
{
"name": "astro-ph0002100.extracted_bib",
"string": "\\begin{thebibliography}\n\n%\\bibitem[Bally et al.{}<1995>]{p:Bal95} \n% Bally, J., Devine, D. \\& Sutherland, R. 1995, In: S. Lizano \\&\n% J.~M. Torrelles (eds.): {Circumstellar Disks, Outflows and Star\n% Formation}, RMAA (Serie de Conferencias... |