Evolution and nucleosynthesis in extremely metal-poor, asymptotic giant branch stars

Iwamoto, Nobuyuki  

We evolve extremely metal-poor, thermally pulsing Asymptotic Giant Branch (AGB) models with the mass range of 1-8 . The ejected chemical yields are obtained by considering mass loss. We find that the 1- and 2- AGB models are not affected by hot bottom burning (HBB). Nevertheless, they produce large amount of Li in an H-flash event. The occurrence of this event is associated with the ingestion of protons from the overlying H-rich envelope into the He convective shell driven by thermal pulse. The resulting Li abundances in the ejecta are higher than the primordial one predicted in Big-Bang nucleosynthesis. The efficient production of Li by the operation of HBB is also confirmed in the models of 4-8 . If these AGB stars have a low-mass companion, it is probable that mass loss from the primary AGB star brings the materials enriched in Li into the secondary star. This makes the surface composition of the secondary Li-rich.