Blue stragglers and variable stars in M3

The BSs in M3 are slightly more centrally concentrated than red giant branch stars while horizontal branch stars are somewhat less concentrated than red giants. The radial distribution of V-selected subgiant and turnoff stars is well fit by a King model with a core radius r(core)=28"+/-2" (90% confidence limits), which corresponds to 1.4pc. Red giant and horizontal branch stars selected in the ultraviolet data (U<18) have a somewhat more compact distribution (r(core)=22.5").

The HST U data consist of 17 exposures acquired over a span of three days. We have used these data to isolate 40 variable stars for which relative astrometry, brightnesses, colors, and light curves are presented. A Kolmogorov-Smirnov test indicates that, typically, the variability for each star is significant at the 95% level.

We identify two variable BS candidates (probably of the SX Phe type) out of a sample of ~25 BSs in which variability could have been detected. Most of the variables are RR Lyrae stars on the horizontal branch. All of them have periods P>~8h.

Addresses: Guhathakurta P. raja@stsci.edu Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218 Yanny B. yanny@guinness.ias.edu Bahcall J.N. jnb@sns.ias.edu Institute for Advanced Study, Princeton, New Jersey 08540 Schneider D.P. dps@astro.psu.edu Institute for Advanced Study, Princeton, New Jersey 08540 and Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, Pennsylvania 16802