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T. Blöcker, T. Driebe and F. Herwig:
AGB Evolution with Overshoot: Hot Bottom
Burning vs. Dredge-Up
Abstract (poster) for:
Astronomische Gesellschaft Meeting Abstracts (AGM 15, P25)
New Astrophysical
Horizons
Annual Scientific Meeting of the Astronomische Gesellschaft, Sep 21-25,
1999, Göttingen, Germany
Abstract.
In recent stellar evolution calculations (Herwig et al. 1997) we have
considered diffusive overshoot for all convective boundaries
which leads to a considerable change in the models. This method
provides for
AGB stars a sufficient amount of dredge up to form
low-mass carbon stars as required from observations. Additionally it
leads to
the formation of C13 as neutron source to drive
the s-process in these stars.
However the consequences for massive AGB stars, which suffer from hot
bottom
burning, remains to be investigated in detail. Hot
bottom burning, i.e. the penetration of the convective envelope into
the
hydrogen burning shell, provides lithium-rich AGB stars
and may prevent the carbon star stage for almost the whole AGB lifetime
by
turning C12 into C13 and N14.
We continue to extend our computations to hot bottom burning models
including
a coupled treatment of nucleosynthesis and
mixing. Due to overshoot the models show very efficient dredge up.
The consequence of the simultaneous treatment of mixing and
burning is investigated and the competition between hot bottom burning
and
dredge up with respect to the chemical evolution is
studied.
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