HST OBSERVATIONS OF BLUE STRAGGLER STARS IN THE CORE OF THE GLOBULAR-CLUSTER M3

The core of the Galactic Globular Cluster M 3 (NGC 5272) has been obse rved with the WFPC2 through the filters F255W, F336W, F555W, and F814W . Using these observations along with a thorough reanalysis of earlier catalogs, we have produced a catalog of blue straggler stars (BSS) sp anning the cluster. Earlier studies and the fainter part of our sample suffer severe selection biases. Our analysis is based on a more relia ble bright global sample of 122 BSS. We confirm earlier suggestions th at the radial BSS distribution in M 3 is bimodal. It is strongly peake d in the center, has a clear dip 100-200 '' from the center, and rises again at larger radii. The observed distribution agrees with the dyna mical model of Sigurdsson et al. (1994) which takes into account both star collisions and merging of primordial binaries for the origin of B SS. The observed luminosity functions of BSS in the inner and outer pa rts of the cluster are different. Interpreting these using the models of Bailyn & Pinsonneault (1995), we suggest that the BSS in the inner cluster are formed by stellar collisions and those in the outer cluste r from merging primordial binaries.