Blue Stragglers, Young White Dwarfs, and UV‐Excess Stars in the Core of 47 Tucanae

We used a set of archived HST/WFPC2 images to probe the stellar population inthe core of the nearby Galactic Globular Cluster (GGC) 47 Tuc. From theultraviolet (UV) Color Magnitude Diagrams (CMDs) obtained for ~4,000 starsdetected within the Planetary Camera (PC) field of view we have pinpointed anumber of interesting objects: (i) 43 blue stragglers stars (BSSs) including 20 new candidates; (ii) 12 bright (young) cooling white dwarfs (WDs) at the extreme blue regionof the UV-CMD; (iii) a large population of UV-excess (UVE) stars, lying betweenthe BSS and the WD sequences. The WD candidates identified here define a cleanpattern in the CMD, which define the WD cooling sequence. Moreover, both thelocation on the UV-CMDs and the number of WDs are in excellent agreement withthe theoretical expectations. The UVE stars discovered here represent thelargest population of anomalous blue objects ever observed in a globularcluster -- if the existence of such a large population is confirmed, we havefinally found the long-searched population of interacting binaries predicted bythe theory. Finally, we have investigated the feasibility of the opticalidentification of the companions of the binary X-ray sources recently detectedby CHANDRA and of binary millisecond pulsars (MSPs) residing in the core of 47Tuc. Unfortunately, the extreme faintness expected for the MSP companionstogether with the huge stellar crowding in the cluster center preventstatistically reliable identifications based only on positional coincidences.Comment: 27 pages, LaTex, 4 Postscript figures. Astrophysical Journal, in pres