Determination of mass-loss rates of PG 1159 stars from FUV spectroscopy

L. Koesterke1 and K. Werner2

1Universität Potsdam, Institut für Physik, Astrophysik
2Institut für Astronomie und Astrophysik der Universität Tübingen

We determine mass-loss rates of four hot, low-gravity PG 1159 stars which are regarded as immediate descendants of Wolf-Rayet central stars of planetary nebulae (i.e. early spectral type [WCE]). The sample consists of classical hydrogen-deficient PG 1159 stars (K1-16, NGC 246, RX J2117.1+3412) as well as one object of the very rare "hybrid" subtype which also exhibits hydrogen lines (NGC 7094). The sample is complemented by the famous [WC]-PG 1159 transition object Abell 78. Our analysis is based on the O VI 1032/1038 Å resonance line which is the strongest wind-feature in these objects. FUV observations were performed with the Berkeley spectrograph during the ORFEUS-SPAS II mission. One spectrum is taken from archive data of the ORFEUS-SPAS I mission and another one was obtained with the Hopkins Ultraviolet Telescope during the Astro-2 mission. We find mass-loss rates ranging between 10-8 ... 10-7 solar masses per year, as compared to the [WCE] stars which have mass-loss rates of about 10-5.5 ... 10-6.5 solar masses per year. By comparison with theory we conclude that the wind of PG 1159 stars is driven by radiation pressure.

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