Envelope burning over-luminosity: a challenge to synthetic TP-AGB models
P. Marigo 1, 2
Received 7 May 1998 / Accepted 10 September 1998
Until recently synthetic AGB models had not taken into account the break-down of the core mass-luminosity () relation due to the occurrence of envelope burning in the most massive ( for Pop. II and for Pop. I) and luminous () stars.
Marigo et al. (1998) made the first attempt to consistently include the related over-luminosity effect (i.e. above the relation) in synthetic TP-AGB calculations. The method couples complete envelope integrations with analytical prescriptions, these latter being presently updated with the highly detailed relations by Wagenhuber & Groenewegen (1998).
In this paper the reliability of the solution scheme is tested by comparison with the results of complete evolutionary calculations for a AGB star undergoing envelope burning (Blöcker & Schönberner 1991; Blöcker 1995).
Indeed, the method proves to be valid as it is able to reproduce with remarkable accuracy several evolutionary features of the star (e.g. rate of brightening, luminosity evolution as a function of the core mass and envelope mass for different mass-loss prescriptions) as predicted by full AGB models.
Basing on the new solution method, we present extensive synthetic TP-AGB calculations for stars with initial masses of and , and three choices of the initial metallicity, i.e. , , and . Three values of the mixing-length parameter are used, i.e. . We investigate the dependence of envelope burning on such stellar parameters (M, Z, and ). The comparison between different cases gives hints on the interplay between envelope burning over-luminosity and mass loss, and related effects on TP-AGB lifetimes.
Key words: stars: mass-loss stars: AGB and post-AGB stars: evolution
Send offprint requests to: Paola Marigo (firstname.lastname@example.org)
© European Southern Observatory (ESO) 1998
Online publication: November 9, 1998