The contribution of primordial binaries to the blue straggler population in 47 Tucanae

Abstract

The recent observation (Ferraro et al. 2003b) of the blue straggler population in 47 Tucanae gives the first detailed characterization of their spatial distribution in the cluster over its entire volume. Relative to the light distribution, blue stragglers appear to be overabundant in the core and at large radii. The observed surface density profile shows a central peak, a zone of avoidance and a rise beyond twenty core radii. In light of these findings we explored the evolution of blue stragglers mimicking their dynamics in a multi-mass King model for 47 Tucanae. We find that the observed spatial distribution can not be explained within a purely collisional scenario in which blue stragglers are generated exclusively in the core through direct mergers. An excellent fit is obtained if we require that a sizable fraction of blue stragglers is generated in the peripheral regions of the cluster inside primordial binaries that evolve in isolation experiencing mass-transfer.