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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint A/98

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

L. Koesterke(1) and K. Werner(2)

(1)Institut für Physik, Astrophysik, Universität Potsdam, Am Neuen Palais 10, D-14469 Potsdam, Germany
(2)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

1998, Astrophysical Journal, 500, 55

Abstract. 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 (K 1-16, 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 log(Mdot/M_sun per yr) = -8 ... -7, as compared to the [WCE] stars which have mass-loss rates of about log(Mdot/M_sun per yr) = -5.5 ... -6.5. By comparison with theory we conclude that the wind of PG 1159 stars is driven by radiation pressure.

Key words: stars: AGB and post-AGB - stars: atmospheres - stars: evolution - stars: mass-loss - stars: chemically peculiar - ultraviolet: stars

Paper (264k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de)
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