Lithium synthesis in low metallicity AGB stars

We evolve thermally pulsing AGB star models in the mass range of 1 - 8 M-circle dot. The metallicity of the models is assumed to be [Fe/H] similar or equal to -3. Mass loss is taken into account to investigate the abundance patterns of the yields ejected from the AGB models. In the 1 and 2 M-circle dot AGB models hot bottom burning (HBB) does not take place at the base of the convective envelope during interpulse phases, but the low-mass models produce Li-7 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-flash driven convective shell during thermal pulse phase. The resulting Li-7 abundances are higher than the primordial one based on the analysis of the WMAP data. The present investigation also confirms the efficient production of Li-7 by the HBB in the intermediate-mass (4 - 8 M-circle dot) AGB stars. If these AGB stars belong to a binary system with a low-mass companion, mass loss from the primary AGB star transfers the materials enriched in Li-7 to the surface of the secondary star and makes the surface composition Li-rich. The formation of the Li-rich stars, however, strongly depends on the mass loss history and binary separation. The nucleosynthesis of the other light elements up to the phosphorus is also followed until the end of the AGB phase. We find that the yields of the low metallicity AGB stars well reproduce the abundance patterns of extremely metal-poor stars.