Production of Lithium and Heavy Elements in AGB Stars Experiencing PIEs

Abstract

Asymptotic giant branch (AGB) stars can experience proton ingestion events (PIEs), leading to a rich nucleosynthesis. During a PIE, the intermediate neutron capture process (i-process) develops, leading to the production of trans-iron elements. It is also suggested that lithium is produced during these events. We investigate the production of lithium and trans-iron elements in AGB stars experiencing a PIE with 1Mini/M⊙3 and −3[Fe/H]0. We find that lithium is produced in all PIE models with surface abundances 3 A(Li) 5. The surface enrichment and overall AGB lithium yield increases with decreasing stellar mass. The lithium enrichment is accompanied by a production of 13C with 312C/13C 9 at the surface just after the PIE. AGB stars experiencing PIE may be related to J-type carbon stars whose main features are excesses of lithium and13C. In addition to Li and 13C, heavy elements (e.g., Sr, Ba, Eu, Pb) are significantly produced in low-metallicity stars up to [Fe/H] ≃−1. The yields of our models are publicly available. Additionally, of interest to the Li nucleosynthesis, we provide an updated fitting formula for the 7Be(e−,νe)7Li electron capture rate.

Keywords

• nucleosynthesis
• lithium
• nuclear reactions
• AGB stars