AGB evolution with overshoot: hot bottom burning and dredge up

Abstract

We calculated models of massive AGB stars with a self-consistent coupling of time-dependent mixing and nuclear burning for 30 isotopes and 74 reactions. Overshoot with an exponentially declining velocity field was considered and applied during all stages of evolution and in all convective regions. Very efficient 3rd dredge-up was found even overcompensating the growth of the hydrogen-exhausted core after a few thermal pulses. Hot bottom burning occurs for M>4Msol within the sequences with overshoot. Carbon star formation in these more massive AGB stars is delayed or even prevented by hot bottom burning despite the very efficient dredge-up. With the simultaneous treatment of mixing and burning the formation of Li-rich AGB stars due to the Cameron-Fowler mechanism was followed. For a 6Msol model the maximum Li abundance was found to be epsilon(Li7)=4.4.