A Population of Binaries in the Asymptotic Giant Branch of 47 Tucanae?

Abstract

We have used a set of archived Hubble Space Telescope Advanced Camera for Surveys images to probe the evolved populations of the globular cluster 47 Tucanae. We find an excess of asymptotic giant branch (AGB) stars in the cluster core. We interpret this feature as the signature of an extrapopulation likely made by the progeny of massive stars originated by the evolution of binary systems. Indeed, the comparison with theoretical tracks suggests that the AGB population of 47 Tuc can be significantly contaminated by more massive stars currently experiencing the first ascending red giant branch.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. Also based on WFI observations collected at the European Southern Observatory, La Silla, Chile, within the observing programs 62.L-0354 and 64.L-0439.