Accretion of gas by globular cluster stars

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, 5 avenue de Cointe, 4000 Liège, Belgium
² Institut d'Astronomie et d'Astrophysique, CP 226, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium
³ European Southern Observatory, Casilla 19001, Santiago 19, Chile

Corresponding author: A. Thoul, thoul@astro.ulg.ac.be

Received: 17 July 2001
Accepted: 7 December 2001

Abstract

Some recent observations of the abundances of s-process, r-process, and α elements in metal-poor stars have led to a new scenario for their formation. According to this scenario, these stars were born in a globular cluster and accreted the s-process enriched gas expelled by cluster stars of higher-mass, thereby modifying their surface abundances. Later on, these polluted stars evaporated from the globular cluster to constitute an important fraction of the current halo population. In addition, there are now many direct observations of abundance anomalies not only in globular cluster giant stars but also in subgiant and main-sequence stars. Accretion again provides a plausible explanation for (at least some of) these peculiarities. Here we investigate further the efficiency of the accretion scenario. We find that in concentrated clusters with large escape velocities, accretion is very efficient and can indeed lead to major modifications of the stellar surface abundances.