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The role of convective boundaries

Published online by Cambridge University Press:  25 May 2016

F. Herwig ,
T. Blöcker  and
D. Schönberner
F. Herwig
Affiliation:
Institut für Physik, Universität Potsdam, Germany
T. Blöcker
Affiliation:
Max-Planck-Institut für Radioastronomie, Bonn, Germany
D. Schönberner
Affiliation:
Astrophysikalisches Institut Potsdam, Germany

Abstract

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We investigate the influence of convective overshoot on stellar evolution models of the thermal pulse AGB phase with MZAMS = 3M⊙. 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 13C-pocket can form after the third dredge-up event which may be crucial for n-capture nucleosynthesis.

Type
Part 1. Basic Facts, Structure, Evolution, Nucleosynthesis
Information
Symposium - International Astronomical Union , Volume 191: Asymptotic Giant Branch Stars , 1999 , pp. 41 - 46
Copyright
Copyright © Astronomical Society of the Pacific 1999 

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