Stellar evolution of low and intermediate-mass stars. IV. Hydrodynamically-based overshoot and nucleosynthesis in AGB stars.
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. (1996A&A...313..497F) 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, M_ZAMS_=3Msun_). Our calculations show the 3^rd^ dredge-up already at the 7^th^ thermal pulse (TP), and the dredge-up parameter reaches λ=0.6 during the next five pulses. Accordingly, the amount of dredged up ^12^C is up to 10^-3^Msun_. Our models develope a small so-called ^13^C-pocket consisting of a few 10^-7^ Msun_. Finally, this treatment of boundaries of convective regions leads to intershell abundances of typically (^4^He/^12^C/^16^O)=(23/50/25) (compared to (70/26/1) in the standard treatment).