THE PHOTOSPHERIC TEMPERATURE AND METAL ABUNDANCE OF THE COMPACT STAR H1504 + 65

We present a new analysis of an EXOSAT low-energy telescope observation of the hot compact star HI504 + 65. Earlier results had failed to take into account the large point-spread function produced by the boron filter, and hence the count rate had been underestimated by a large factor. On comparing the data with a new grid of model atmospheres containing CNO metals we are able to estimate the temperature, line-of-sight column density and photospheric elemental abundances for the star. Contrary to earlier suggestions it appears that H1504 + 65 is not devoid of He and may also have significant H present in its photosphere. These results are consistent with H1504 + 65 being the hottest member of the PG1159-035 spectroscopic group of degenerate stars and not a peculiar individual star. © 1990 Oxford University Press. All rights reserved.