The role of lithium production in massive AGB and super--AGB stars for the understanding of multiple populations in Globular Clusters

TL;DR

This paper investigates lithium production in massive AGB and super-AGB stars and its implications for understanding the chemical evolution and multiple populations in globular clusters.

Contribution

It provides new estimates of lithium yields from AGB and super-AGB stars, highlighting the impact of mass loss uncertainties on lithium enrichment in globular clusters.

Findings

Large lithium yields from super-AGB stars under standard mass loss assumptions

Lithium production varies significantly with stellar mass and physical structure

Uncertainties in mass loss rates critically affect lithium yield predictions

Abstract

Lithium is made up in the envelopes of massive Asymptotic Giant Branch (AGB) stars through the process of Hot Bottom Burning. In Globular Clusters, this processing is one possible source of the hot-CNO burning whose nuclear products are then ejected into the intracluster medium and take part in the formation of a second stellar generation, explaining the peculiar distribution of chemical elements among the cluster stars. We discuss the lithium yields from AGB stars in the mass range 3-6.3 Msun, and from super-AGB stars of masses in the range 6.5-9 Msun for metallicity Z=0.001. The qualitative behaviour of these yields is discussed in terms of the physical structure of the different masses. Although many uncertainties affect the other yields of these stars (e.g. O, Na and Mg), even larger uncertainties affect the lithium yield, as it depends dramatically on the adopted description of mass loss. When we adopt our standard mass loss formulation, very large yields are obtained especially for the super-AGB stars, and we discuss their possible role on the lithium abundance of second generation stars in globular clusters.