CATALOG AND LUMINOSITY FUNCTION OF WHITE-DWARFS DETECTED IN THE ROSATALL-SKY SURVEY

This paper contains a compilation of all white dwarf stars known to ha ve been detected at soft X-ray wavelengths by the Position Sensitive P roportional Counter onboard ROSAT during the all-sky survey phase of t he mission. Out of the similar to 55,000 X-ray sources which have been detected in the ROSAT all-sky survey, only 175 are white dwarfs. Most (161) are of type DA, while there are 8 PG 1159, 3 DAO, and 3 DO star s detected. These numbers are compared to the results of the ROSAT Wid e Field Camera survey and the log N - log S relation is used to estima te the completeness of the catalogue. The sky coverage of the ROSAT al l-sky survey is used to calculate the X-ray luminosity function of DA white dwarfs. We find that only 10% of hot (i.e. T-eff > 20,000 K) DAs are X-ray luminous (i.e. L(X) > 10(29) ergs s(-1)). We also use this sample to infer that one out of every four DAs are in binary systems w ith a late-type companion. This work represents the first all-sky X-ra y survey of white dwarfs to a uniform sensitivity limit.