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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
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 =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 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: email@example.com
Online publication: June 18, 1999