SIMBAD references

This paper contains a compilation of all white dwarf stars known to have been detected at soft X-ray wavelengths by the Position Sensitive Proportional Counter onboard ROSAT during the all-sky survey phase of the mission. Out of the ∼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 stars detected. These numbers are compared to the results of the ROSAT Wide Field Camera survey and the log N - log S relation is used to estimate the completeness of the catalogue. The sky coverage of the ROSAT all-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>20,000K) DAs are X-ray luminous (i.e. L_X>10²⁹ergs/s). We also use this sample to infer that one out of every four DAs are in binary systems with a late-type companion. This work represents the first all-sky X-ray survey of white dwarfs to a uniform sensitivity limit.