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Astron. Astrophys. 349, L5-L8 (1999)

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3. The AGB starting model

We start with an AGB model with [FORMULA] which has been evolved over 22 thermal pulses, including convective overshoot at all convective boundaries. The treatment and efficiency (f=0.016) of overshoot is the same as in Herwig et al. (1997). In comparison to models without overshoot the intershell region is much stronger enriched in carbon and oxygen (mass fractions [He/C/O]=[0.35/0.43/0.19]), which causes a stronger third dredge-up (Herwig et al., 1999). At the [FORMULA] thermal pulse (TP) the hydrogen-free core has a mass of [FORMULA] and dredge-up starts to operate, leading to a carbon star model at the last computed TP. At this stage the model star has a total mass of [FORMULA] and [FORMULA]. We then artificially increase the mass loss ([FORMULA]) in order to force the model to leave the AGB at the right phase to develop a very late thermal pulse. This procedure is justified for this exploratory work because it does not affect the nucleosynthesis and mixing during the very late TP.

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999