2005A&A...434..707W

object{H1504+65} is a young white dwarf with an effective temperature of 200000K 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 H1504+65 with those of Procyon and αCen 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.