AAS 201st Meeting, January, 2003
Session 7. Globular Clusters and Their Contents
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[7.18] A Search for Optical Counterparts of Chandra Sources in Omega Centauri using ACS

D. Haggard, A.D. Fuller, J.L. Dorfman, A.M. Cool (San Francisco State University), J. Anderson (U.C. Berkeley), P.D. Edmonds (Harvard University), M.B. Davies (University of Leicester)

The globular cluster Omega Centauri, with its high mass and large, moderate density core, is of interest both for its population of primordial binaries and for the large number of tidal-capture and/or exchange-collision binaries it may harbor. We have obtained a 3x3 mosaic of Wide Field Camera pointings with HST's Advanced Camera for Surveys, covering a 10'x10' field out to the cluster's half-mass radius. Containing ~1.7 million detected stars, the resulting mosaic represents the most complete image of Omega Cen yet obtained. Here we report preliminary findings of a search in these data for optical counterparts to more than 100 faint X-ray sources (Lx ~2 x 1030 - 5 x 1032 erg-s-1) detected in our prior study of Omega Cen using the Chandra X-ray Observatory. Cluster X-ray sources are likely to consist primarily of accreting binary stars and close detached binaries with active coronae. Significant numbers of active galaxies in the background are also expected to be present. Using B, R, and H-alpha images, we are searching for optical counterparts that are H-alpha-bright and blue, as signatures of accretion in cataclysmic variables and/or quiescent low-mass X-ray binaries. Active binaries (e.g., BY Draconis stars) may appear as weaker H-alpha emitters lying on or slightly redward of the main sequence. This work is supported by NASA grant GO-9442 from the Space Telescope Science Institute.

The author(s) of this abstract have provided an email address for comments about the abstract: dhaggard@stars.sfsu.edu

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.