The small blue straggler star population in the dense galactic globular cluster NGC 6752

We used high-resolution Hubble Space Telescope (HST)-WFPC2 and wide-field ground-based observations to construct a catalog of blue straggler stars (BSSs) that spans the entire radial extent of the globular cluster NGC 6752. The BSS sample is the most extensive ever obtained for this cluster. Although NGC 6752 is a high-density cluster with a large binary population, we found that its BSS content is surprisingly low: the specific number of BSSs is among the lowest ever measured in a cluster. The BSS distribution is highly peaked in the cluster center, shows a rapid decrease at intermediate radii, and rises again at larger distances. This distribution closely resembles those observed in M3 and 47 Tuc by Ferraro and coworkers. To date, BSS surveys covering the central regions with HST and the outer regions with wide-field CCD ground-based observations have been performed for only these three clusters. Despite the different dynamical properties, a bimodal radial distribution has been found in each. A detailed comparison of observed BSS luminosity and temperature distributions with theoretical models reveals a population of luminous, hot BSSs that is not easily interpreted.