Abstract
We present a summary of the white dwarf detections in the ROSAT X-ray and EUV surveys. Although it is not yet possible to calculate a formal X-ray luminosity function, we use survival statistics to calculate an integral X-ray luminosity distribution for the DA white dwarfs. The result is that most hot (T eff > 20,000 K) DA white dwarfs are not strong X-ray sources. Some 75% of all hot DAs have X-ray luminosities less than that of Sirius B (i.e. 7 x 1028 ergs s-1), and no DAs hotter than 60,000 K have yet been detected as X-ray sources. We interpret this to mean that elements heavier than He (e.g. C, O, Fe) are present in the atmospheres of most hot DA white dwarfs.
Published Version
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