Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
F. Herwig, T. Blöcker and D.
Schönberner:
The Role of Convective Boundaries
Proceedings of Asymptotic
Giant Branch Stars , IAU Symp. 191,
T. Le Bertre, A. Lebre, C. Waelkens (eds.), Astr. Soc. Pacific, p.
41-46 (1999)
Abstract.
We investigate the influence of convective overshoot
on stellar evolution models of the thermal pulse AGB phase
with M_ZAMS = 3 Msol.
An exponential diffusive overshoot algorithm is applied to all
convective boundaries during all evolutionary stages.
We demonstrate that overshooting at the bottom of the
pulse-driven convective zone, which forms in the intershell during the
He-shell
flash, leads to more efficient third dredge-up. Some overshoot
at the bottom of the convective envelope removes the
He-H discontinuity, which would otherwise prohibit the occurrence
of the third dredge-up for this stellar mass. However, no correlation
between the amount of envelope overshoot and the efficiency of the
third dredge-up has been found.
Increasingly efficient third dredge-up eventually leads
to a carbon star model.
Due to the partial mixing efficiency in the overshoot region a
C13-pocket can form after the third dredge-up event which may be
crucial for
n-capture nucleosynthesis.