The role of convective boundaries

Abstract

We investigate the influence of convective overshoot on stellar evolution models of the thermal pulse AGB phase with M_Z_A_M_S = 3M_sun. 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 "1"3C-pocket can form after the third dredge-up event which may be crucial for n-capture nucleosynthesis. (orig.)15 refs.Available from TIB Hannover: RR 7310(98-38) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman