Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
T. Blöcker, F. Herwig and T .Driebe:
AGB evolution with overshoot: hot bottom
burning and dredge-up
in
The
Changes in Abundances in Asymptotic Giant Branch Stars,
Mem. Soc. Astron. Ital. 71, 711-718 (2000)
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.
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