The HEAO-1 soft X-ray survey of cataclysmic variable stars

A survey of the soft X-ray emission from 206 cataclysmic variable stars, including dwarf novae in optically quiescent states, classical novae, recurrent novae, nova-like objects and polars, is reported. This is an extension of a previous survey of dwarf novae in outbursts by Córdova et al. (1980a). The number of surveyed stars that correspond to features > 2 σ is not in excess of the number of chance coincidences expected on the basis of a random sample of positions distributed over the entire sky. While a few cataclysmic variables have been previously identified as X-ray sources, the results of this survey imply that cataclysmic variables as a class must be, at best, low-luminosity X-ray sources with fluxes below the HEAO-1 A2 detector's sensitivity limit of a few times 10−11 erg cm−2 s−1 in the energy range 0.1–3 keV. The X-ray luminosities of the cataclysmic variables are consistent with predictions from disc accretion models, provided that a wide range of accretion rates apply.