The Blue Straggler Population of the Globular Cluster M5

Abstract

By combining high-resolution HSTand wide-field ground-based observations, in ultraviolet and optical bands, we study the blue straggler star (BSS) population of the galactic globular cluster M5 (NGC 5904) from its very central regions up to its periphery. The BSS distribution is highly peaked in the cluster center, decreases at intermediate radii and rises again outward. Such a bimodal distribution is similar to those previously observed in other globular clusters (M3, 47 Tucanae, NGC 6752). As for these clusters, dynamical simulations suggest that, while the majority of BSSs in M5 could be originated by stellar collisions, a significant fraction (20%-40%) of BSSs generated by mass transfer processes i n primordial binaries is required to reproduce the observed radial distribution. A candidate BSS has been detected beyond the cluster tidal radius. If confirmed, this could represent an interesting case of an "evaporating" BSS. © 2007. The American Astronomical Society. All rights reserved.