H- and He-burning central stars and the evolution to white dwarfs.pdf

Planetary Nebulae and Their Role in the Universe IAU Symposium 209, 2002 M. Dopita, S. Kwok and R.S. Sutherland, eds. H- and He-burning central stars and the evolution to white dwarfs T. Bl¨ocker Max–Planck–Institut f¨ur Radioastronomie, 53121 Bonn, Germany 2 0 Abstract. The structure and evolution of central stars of planetary 0 nebulae (CSPNe) is reviewed. CSPNe represent the rapid transitional 2 stage between the Asymptotic Giant Branch (AGB) and the white-dwarf l domain. It is shown that the whole evolution off the AGB through the u J central-star regime depends on the evolutionary history. The detailed 8 evolution into a white dwarf is controlled by the internal stellar structure which, in turn, is determined by the duration of the preceding AGB 1 evolution and therefore by the AGB mass-loss history. The evolution of v hydrogen-deficient central stars has been a matter of debate since many 1 6 years. Convective overshoot appears to be a key ingredient to model these 1 objects. Various thermal-pulse scenarios with inclusion of overshoot are 7 discussed, leading to surface abundances in general agreement with those 0 observed for Wolf-Rayet central stars. 2 0 / h p 1. Introduction - o r Central stars of planetary nebulae (CSPNe) represent the rapid transitional t s stage between the Asympto