Spectral analyses of Wolf-Rayet type central stars

H. Todt1, M. Peña2, W.-R. Hamann1, G. Gräfener3

1 University of Potsdam, Institute of Physics and Astronomy, 14476 Potsdam, Germany
2 Instituto de Astronomia, Universidad Nacional Autonoma de Mexico
3 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland

A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. These stars are commonly considered as the progenitors of H-deficient white dwarfs. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen, most of them showing Wolf-Rayet-like emission line spectra and are therefore classified as of spectral type [WC]. Moreover, a few CSPNe of other Wolf-Rayet spectral subtypes have been identified in the last years, e.g. PB 8, which is of spectral type [WN/C]. We performed spectral analyses for a number of Wolf-Rayet type central stars with the help of our Potsdam Wolf-Rayet (PoWR) model code for expanding atmospheres to determine meaningful stellar parameters. The results of our analyses are presented here in the context of stellar evolution and white dwarf formation. We discuss the problems of a uniform evolutionary channel for [WC] stars as well as constraints of the formation of [WN/WC] subtype stars.

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