TITLE: Morita equivalence for *-algebras
QUESTION [11 upvotes]: This is a reference request.  I'm looking for a definition of Morita equivalence of *-algebras, as described below.  If anyone thinks that this is not the right way to define Morita equivalence of *-algebras, I'd be interested to hear that also.

By a *-algebra, I mean an algebra equipped with an anti-involution ${}^*$, $(ab)^* = b^*a^*$.  (I'm mainly interested in finite-dimensional algebras.)
Recall that a Morita equivalence of algebras $A$ and $B$ consists of (1) a pair of bimodules $_AM_B$ and $_BN_A$, and (2) bimodule isomorphisms $f:{}_A(M\otimes N)_A \to {}_AA_A$ and $g:{}_B(N\otimes M)_B \to {}_BB_B$ such that (3) $f$ and $g$ satisfy the zig-zag identities.
If $A$ and $B$ are *-algebras, it seems to me that the definition of Morita equivalence should be modified (enhanced) as follows.  
First, note that the *-structure of $A$ allows us to convert between left and right $A$-modules, and similarly for $B$.  In particular, to any $A$-$B$ bimodule $_AX_B$ there is associated a $B$-$A$ bimodule $_BX^*_A$.  The first modification to the definition of Morita equivalence is to replace $_BN_A$ above with $_BM^*_A$.
Next, note that both $_AA_A$ and $_A(M\otimes M^*)_A$ have involutions coming from the *-structure.  The second (and final) modification to the definition is to require that the isomorphism $f:{}_A(M\otimes M^*)_A \to {}_AA_A$ intertwine with these two involutions, and similarly for $g:{}_B(M^*\otimes M)_B \to {}_BB_B$.

Recall that an (ordinary) Morita equivalence gives an isomorphism between 0-th Hochschild homologies $HH_0(A) \cong HH_0(B)$.  A *-structure on $A$ gives rise to an involution of $HH_0(A)$.  The isomorphism $HH_0(A) \cong HH_0(B)$ coming from an ordinary Morita equivalence need not commute with the involutions on either side, but the above enhanced Morita equivalences do guarantee compatibility with the involutions on $HH_0$.

So, repeating my initial question, where can i find the above definition in the literature?

REPLY [5 votes]: Usually I do not want to make to much of advertisement for my own stuff, but here it matches only too well: in a series of papers Henrique Bursztyn and myself developped the theory of Morita equivalence and inner product bimodules  for *-algebras in quite some details. This builds on one hand on the work of Ara, already mentioned in Benjamin Steinberg's answer. On the other hand, we were looking for generalizations of Rieffel's notion of strong Morita equivalence since we also wanted to incorporate positivity aspects. Thus our setting was to consider *-algebras over ordered rings like the formal power series used in deformation theory. You can find all this on my homepage together with a (not yet complete) lecture note. Therein you find also a nice categorical framework to compute and describe lots of Morita invariants and a detailed comparison of the various Morita theories (with/out *-involution with/out positivity...).