Determination of mass-loss rates of PG 1159 stars from FUV spectroscopy
L. Koesterke1 and K. Werner2
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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