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Astron. Astrophys. 347, L9-L13 (1999)

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Letter to the Editor

The EUV spectrum of the unique bare stellar core H1504+65 *

Klaus Werner 1 and Burkhard Wolff 2

1 Institut für Astronomie und Astrophysik, Universität Tübingen, D-72076 Tübingen, Germany
2 Institut für Theoretische Physik und Astrophysik, Universität Kiel, D-24098 Kiel, Germany

Received 25 May 1999 / Accepted 5 June 1999


We performed a spectral analysis of the EUVE spectrum and ROSAT data of the unique object H1504+65, which is an extremely hot post-AGB star entering the white dwarf cooling sequence. It is the only pre-white dwarf known, whose surface is free of hydrogen and helium, hence, it represents the bare core of a former AGB star. The EUV spectrum (75-150 Å) is dominated by strong O VI lines and we can identify a number of Ne VII lines.

EUVE and ROSAT data can be fitted with models between [FORMULA]=170 000 K and 200 000 K. We derive an extraordinarily high neon abundance (2%-5% by mass, i.e. 20-50 times solar) which we confirm by an optical Ne VII line detected in a Keck HIRES echelle spectrum. This abundance is expected for [FORMULA] processed matter and corroborates our understanding of H1504+65 as a C-O stellar core which has lost its entire H- and He-rich envelopes.

Key words: stars: abundances – stars: atmospheres – stars: evolution – stars: AGB and post-AGB – stars: white dwarfs – stars: individual: H1504+65

* Based on observations with the Extreme Ultraviolet Explorer (EUVE) and ROSAT. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated by the California Institute of Technology and the University of California.

Send offprint requests to: K. Werner

Correspondence to: werner@astro.uni-tuebingen.de

© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999