EDP Sciences
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Volume 421, Number 3, July III 2004
Page(s) 1169 - 1183
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20047154

A&A 421, 1169-1183 (2004)
DOI: 10.1051/0004-6361:20047154

Chandra and FUSE spectroscopy of the hot bare stellar core H 1504+65

K. Werner1, T. Rauch1, 2, M. A. Barstow3 and J. W. Kruk4

1  Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
2  Dr.-Remeis-Sternwarte, Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
3  Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
4  Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

(Received 27 January 2004 / Accepted 6 April 2004)

H 1504+65 is an extremely hot hydrogen-deficient white dwarf with an effective temperature close to 200 000 K. We present new FUV and soft X-ray spectra obtained with FUSE and Chandra, which confirm that H 1504+65 has an atmosphere primarily composed of carbon and oxygen. The Chandra LETG spectrum (60-160 Å) shows a wealth of photospheric absorption lines from highly ionized oxygen, neon, and - for the first time identified in this star - magnesium and suggests relatively high Ne and Mg abundances. This corroborates an earlier suggestion that  H 1504+65 represents a naked C/O stellar core or even the C/O envelope of an O-Ne-Mg white dwarf.

Key words: stars: abundances -- stars: atmospheres -- stars: evolution -- stars: AGB and post-AGB -- stars: white dwarfs -- stars: individual: H 1504+65

Offprint request: K. Werner, werner@astro.uni-tuebingen.de

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