1999A&A...347L...9W

We performed a spectral analysis of the EUVE spectrum and ROSAT data of the unique object H 1504+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 (75-150Å) 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 T_eff=170000K and 200000K. 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 3α processed matter and corroborates our understanding of H 1504+65 as a C-O stellar core which has lost its entire H- and He-rich envelopes.