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Preprint 08/07

HST Spectroscopy of the Hottest White Dwarfs

Thomas Rauch & Klaus Werner

Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany

To be published in: Proceedings of the 41st ESLAB Symposium. The Impact of HST on European Astronomy. 29 May to 1 June, 2007. ESTEC, Noordwijk, Netherlands

Abstract. Spectral analysis needs the observation of lines of successive ionization stages in order to evaluate the ionization equilibrium (of a particular species) which is a sensitive indicator for the effective temperature (T_eff). Since stars with T_eff as high as 100 000 K have their flux maximum in the extreme ultraviolet (EUV) wavelength range and due to the high degree of ionization, most of the metal lines are found in the ultraviolet (UV) range. Thus, high-S/N and high-resolution UV spectra are a pre-requisite for a precise analysis. Consequently, we employed the Faint Object Spectrograph (FOS), the Goddard High Resolution Spectrograph (GHRS), and the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST) in order to obtain suitable data. We present state-of-the-art analyses of the hottest (pre-) white dwarfs by means of NLTE model atmospheres which include the metal-line blanketing of all elements from hydrogen to nickel.
 
Key words: Stars: atmospheres; Stars: AGB and post-AGB

Preprint (86 kb PDF file including figures)

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