On the robustness of H-deficient post-AGB tracks

Abstract

We analyze the robustness of H--deficient post--AGB tracks regarding previous evolution of their progenitor stars and the constitutive physics of the remnants. Our motivation is a recent suggestion of Werner & Herwig (2006) that previous evolution should be important in shaping the final post--AGB track and the persisting discrepancy between asteroseismological and spectroscopical mass determinations. This work is thus complementary to our previous work (Miller Bertolami & Althaus 2006) and intends to shed some light on the uncertainty behind the evolutionary tracks presented there. We compute full evolutionary models for PG1159 stars taking into account different extramixing (overshooting) efficiencies and lifetimes on the TP-AGB during the progenitor evolution. We also assess the effect of possible differences in the opacities and equation of state by artificially changing them before the PG1159 stage. Also comparisons are made with the few H-deficient post--AGB tracks available in the literature. Contrary to our expectations, we found that previous evolution is not a main factor in shaping H--deficient post--AGB tracks. Interestingly enough, we find that only an increase of $\sim50%$ in the intershell opacities at high effective temperatures may affect the tracks as to reconcile spectroscopic and asteroseismologic mass determinations. This forces us to conclude that our previous tracks (Miller Bertolami & Althaus 2006) are robust enough as to be used for spectroscopic mass determinations, unless opacities in the intershell region are substantially different. Our results, then, call for an analysis of possible systematics in the usually adopted asteroseismological mass determination methods.