  We present a study of bar and host disk evolution in a dense cluster
environment, based on a sample of ~800 bright (MV <= -18) galaxies in the Abell
901/2 supercluster at z~0.165. We use HST ACS F606W imaging from the STAGES
survey, and data from Spitzer, XMM-Newton, and COMBO-17. We identify and
characterize bars through ellipse-fitting, and other morphological features
through visual classification. (1) We explore three commonly used methods for
selecting disk galaxies. We find 625, 485, and 353 disk galaxies, respectively,
via visual classification, a single component S'ersic cut (n <= 2.5), and a
blue-cloud cut. In cluster environments, the latter two methods miss 31% and
51%, respectively, of visually-identified disks. (2) For moderately inclined
disks, the three methods of disk selection yield a similar global optical bar
fraction (f_bar-opt) of 34% +10%/-3%, 31% +10%/-3%, and 30% +10%/-3%,
respectively. (3) f_bar-opt rises in brighter galaxies and those which appear
to have no significant bulge component. Within a given absolute magnitude bin,
f_bar-opt is higher in visually-selected disk galaxies that have no bulge as
opposed to those with bulges. For a given morphological class, f_bar-opt rises
at higher luminosities. (4) For bright early-types, as well as faint late-type
systems with no evident bulge, the optical bar fraction in the Abell 901/2
clusters is comparable within a factor of 1.1 to 1.4 to that of field galaxies
at lower redshifts (5) Between the core and the virial radius of the cluster at
intermediate environmental densities, the optical bar fraction does not appear
to depend strongly on the local environment density and varies at most by a
factor of ~1.3. We discuss the implications of our results for the evolution of
bars and disks in dense environments.
