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P. D. Edmonds, C. O. Heinke (CfA), R. L. Gilliland (STScI), J. E. Grindlay (CfA), M. D. Albrow (STScI), P. Guhathakurta, J. H. Howell (UCO/Lick), S. S. Murray (CfA), A. Sarajedini (Wesleyan)
The globular cluster 47 Tuc is ideal for studies of cluster binaries because of its proximity, large mass and diverse range of binary species. We report the use of superb quality Chandra and HST imaging to make optical identifications of X-ray sources in and around the dense core of this cluster. The detailed X-ray results will be described in a separate paper by Grindlay et al. The optical imaging is the deepest ever obtained of this beautiful cluster, involving intensive 8.3 day V/I observations with HST/WFPC2. These observations were optimized for variability work and reach unprecedented sensitivity, with rms noise levels of ~4 mmag per exposure near the main sequence turnoff (and ~650 exposures in each of V and I). Supplementary F336W observations provide good color information. The Chandra images are exquisite, delivering the expected dramatic improvement over ROSAT images and containing over 100 sources within 1' of the cluster center. The positional errors for the brighter Chandra sources are a few tenths of an arcsecond, allowing, for the first time, unambiguous optical identifications. This work is ongoing, but already large numbers of X-ray sources have been identified, including cataclysmic variables, eclipsing binaries and possible low-mass X-ray binaries. Also, interesting limits have been set for X-ray sources (possibly millisecond pulsars) not associated with optically variable stars.
This work is partially supported by HST grant GO-8267.
The author(s) of this abstract have provided an email address for comments about the abstract: pedmonds@cfa.harvard.edu