Rubidium-rich Asymptotic Giant Branch stars in the Magellanic Clouds

Abstract

The Magellanic Clouds (MCs) offer a unique opportunity to study the stellar evolution and nucleosynthesis of massive Asymptotic Giant Branch (AGB) stars in low metallicity environments where distances are known. Rubidium is a key element to distinguish between high mass AGB stars and low mass AGBs or other type of astronomical objects such as massive red supergiant stars. Theoretically, high mass AGBs are predicted to produce a lot of Rb. We present the discovery of massive Rb-rich AGB stars in the MCs, confirming for the first time that these stars also exist in other galaxies. Our findings show that these stars are generally brighter than the standard adopted luminosity limit (Mbol ~ -7.1) for AGB stars. The observations of massive MC AGBs are qualitatively predicted by the present theoretical models. However, these theoretical models are far from matching the extremely high Rb overabundances observed. This might be related with an incomplete present understanding of the atmospheres of these stars.