A ROSAT Survey of Contact Binary Stars

Contact binary stars are common variable stars which are all believed to emit relatively large fluxes of x-rays. In this work we combine a large new sample of contact binary stars derived from the ROTSE-I telescope with x-ray data from the ROSAT All-Sky Survey (RASS) to estimate the x-ray volume emissivity of contact binary stars in the galaxy. We obtained x-ray fluxes for 140 contact binaries from the RASS, as well as 2 additional stars observed by the XMMNewton observatory. From these data we confirm the emission of x-rays from all contact binary systems, with typical luminosities of approximately 1.0 ×10 erg s. Combining calculated luminosities with an estimated contact binary space density, we find that contact binaries do not have strong enough x-ray emission to account for a significant portion of the galactic x-ray background. Subject headings: binaries: close – binaries: eclipsing – stars: activity – stars: variables: other – x-rays: stars