A&A 421, 1169-1183 (2004)

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

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

Corresponding author: K. Werner, werner@astro.uni-tuebingen.de

Received: 27 January 2004
Accepted: 6 April 2004

Abstract

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.