On the Fading of AGB Remnants

Extract

We investigated the question how the evolution of post-AGB models depends on their history, i.e. on their initial mass and AGB evolution. Therefore, we calculated the evolution of a 3 and 5M _⊙ star from the main sequence towards the stage of white dwarfs. These models suffered from 9 and 17 thermal pulses on the AGB, resp., and the common mass-loss law led to final masses of 0.61 and 0.84M _⊙, resp., which are consistent with reasonable initial-final mass relationships. It was found that more massive AGB remnants fade much more slower than hitherto assumed. Thus, we conclude that only a reliable combination of initial and final mass yields the right fading time scales for more massive post-AGB models. To prove that we have recalculated the evolution of the 3M _⊙ model with another mass-loss law leading to 86 thermal pulses and a remnant mass of 0.84M _⊙, a combination which, however, does not comply with initial-final mass relations. Comparing now the post-AGB evolution of the two massive models of equal remnant mass (0.84M _⊙) but different initial masses (3 and 5M _⊙, resp.) yields completely different fading time scales. Thus we confirm by direct calculations the suggestion of Blöcker and Schönberner (1990, A&A 240, L11) that not only the remnant mass but also the initial mass determines the time scales of more massive central stars.