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Preprint 03/02

Iron abundance in hot hydrogen-deficient central stars and white dwarfs from FUSE, HST, and IUE spectroscopy

S. Miksa (1,2), J.L. Deetjen (1), S. Dreizler (1), J.W. Kruk (3), T. Rauch (1), and K. Werner (1)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(2) Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany
(3) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, U.S.A.

To appear in: Astronomy & Astrophysics

Abstract. We present a first systematic investigation of the iron abundance in very hot (T_eff >= 50 000 K) hydrogen-deficient post-AGB stars. Our sample comprises 16 PG1159 stars and four DO white dwarfs. We use recent FUSE observations as well as HST and IUE archival data to perform spectral analyses with line blanketed NLTE model atmospheres. Iron is not detected in any PG1159 star. In most cases this is compatible with a solar iron abundance due to limited quality of HST and IUE data, although the tendency to an iron underabundance may be recognized. However, the absence of iron lines in excellent FUSE spectra suggests an underabundance by at least 1 dex in two objects (K 1-16, NGC 7094). A similar result has been reported recently in the [WC]-PG1159 transition object Abell 78 (Werner et al. 2002). We discuss dust fractionation and s-process neutron-captures as possible origins. We also announce the first identification of sulfur in PG1159 stars.

Key words: Stars: AGB and post-AGB - Stars: atmospheres - Stars: abundances - Stars: evolution - White dwarfs - Ultraviolet: stars

Paper (329k gzip'ed Postscript including figures) (astro-ph/0205058)

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