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Astron. Astrophys. 324, L81-L84

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Letter to the Editor

Stellar evolution of low and intermediate-mass stars

IV. Hydrodynamically-based overshoot and nucleosynthesis in AGB stars

F. Herwig1, T. Blöcker2, D. Schönberner1 and M. El Eid3

1Astrophysikalisches Institut Potsdam, D-14773 Potsdam, Germany (fherwig@aip.de; deschoenberner@aip.de)
2Institut für Astronomie und Astrophysik, Universität Kiel, D-24098 Kiel, Germany (bloecker@astrophysik.uni-kiel.de)
3American University of Beirut, Department of Physics, Beirut, Lebanon (meid@aub.edu.lb)

Received 13 March 1997 / Accepted 20 May 1997


The focus of this study is on the treatment of those stellar regions immediately adjacent to convective zones. The results of hydrodynamical simulations by Freytag et al. (1996) show that the motion of convective elements extends well beyond the boundary of the convectively unstable region. We have applied their parametrized description of the corresponding velocities to the treatment of overshoot in stellar evolution calculations up to the AGB (Pop. I, FORMULA ).

Our calculations show the 3 FORMULA dredge-up already at the FORMULA thermal pulse (TP), and the dredge-up parameter reaches FORMULA during the next five pulses. Accordingly, the amount of dredged up 12C\ is up to FORMULA . Our models develope a small so-called 13C-pocket consisting of a few FORMULA . Finally, this treatment of boundaries of convective regions leads to intershell abundances of typically (4He/12C/16O)=(23/50/25) (compared to (70/26/1) in the standard treatment).

Key words: Stars: evolution - Stars: AGB, post-AGB - Stars: abundances

Send offprint requests to: F. Herwig

© European Southern Observatory (ESO) 1997