A Deep Multiwavelength View of Binaries in Omega Centauri
  We summarize results of a search for X-ray-emitting binary stars in the
massive globular cluster Omega Centauri (NGC 5139) using Chandra and HST.
ACIS-I imaging reveals 180 X-ray sources, of which we estimate that 45-70 are
associated with the cluster. We present 40 identifications, most of which we
have obtained using ACS/WFC imaging with HST that covers the central 10'x10' of
the cluster. Roughly half of the optical IDs are accreting binary stars,
including 9 very faint blue stars that we suggest are cataclysmic variables
near the period limit. Another quarter comprise a variety of different systems
all likely to contain coronally active stars. The remaining 9 X-ray-bright
stars are an intriguing group that appears redward of the red giant branch,
with several lying along the anomalous RGB. Future spectroscopic observations
should reveal whether these stars are in fact related to the anomalous RGB, or
whether they instead represent a large group of "sub-subgiants" such as have
been seen in smaller numbers in other globular and open clusters.
