The role of convective boundaries
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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.
6 pages including 3 PostScript figures, also available from http://www.astro.physik.uni-potsdam.de/astro_literatur.html and from http://www.speckle.mpifr-bonn.mpg.de/publications.html, IAU Symp. 191 "AGB Stars", T. Le Bertre, A. Lebre, C. Waelkens (eds.), ASP Conf. Series
6 pages including 3 PostScript figures, also available from http://www.astro.physik.uni-potsdam.de/astro_literatur.html and from http://www.speckle.mpifr-bonn.mpg.de/publications.html, IAU Symp. 191 "AGB Stars", T. Le Bertre, A. Lebre, C. Waelkens (eds.), ASP Conf. Series