EVOLUTIONARY TRACKS AND OBSERVATIONAL CONSTRAINTS

We have performed stellar calculations for initial masses between 1 an d 7 M. from the main sequence through the AGB towards the stage of whi te dwarfs. Our calculations indicate that massive central stars fade m uch slower than hitherto assumed leading to the prediction that the le ast luminous central stars should have masses of 0.65 M.. It is emphas ized that post-AGB timescales depend strongly on the AGB history. Furt hermore, we discuss the possibility of two thermal pulses during the p ost-AGB evolution.