Line identification in soft X-ray spectra of stellar coronae by comparison with the hottest white dwarf's photosphere: Procyon, α Cen A+B, and H 1504+65

¹ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany e-mail: werner@astro.uni-tuebingen.de
² Harvard-Smithsonian Center for Astrophysics, MS 3, 60 Garden Street, Cambridge, MA 02138, USA

Received: 23 September 2004
Accepted: 8 January 2005

Abstract

H 1504+65 is a young white dwarf with an effective temperature of 200 000 K and is the hottest post-AGB star ever analysed with detailed model atmospheres. Chandra LETG+HRC-S spectra have revealed the richest X-ray absorption line spectrum recorded from a stellar photosphere to date. The line forming regions in this extremely hot photosphere produce many transitions in absorption that are also observed in emission in cool star coronae. We have performed a detailed comparison of Chandra spectra of H 1504+65 with those of Procyon and α Cen A and B. State of the art non-LTE model spectra for the hot white dwarf have enabled us to identify a wealth of absorption lines from highly ionized O, Ne and Mg. In turn, these features have allowed us to identify coronal lines whose origins were hitherto unknown.