The stellar content of wide-angle soft X-ray sky surveys

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Within the next two years the data currently collected by the Gaia satellite (launched in December 2013) will become available for astronomical usage at large. This data is likely to revolutionise astronomy at large and also stellar X-ray astronomy. The Gaia data release specifically implies that a complete stellar catalog containing precise photometry in three bands (two in broad band, one in a narrow band) will become available, and, furthermore, precise parallax and proper motion information will become available for essentially all of the brighter stars. As far as stellar X-ray astronomy is concerned, this implies that basically all stars that have been/will be detected in the framework of the ROSAT all-sky survey, the XMM-Newton slew survey and the future eROSITA all-sky survey (to be conducted between 2017-2021) will have precisely known parallaxes and hence distances, thus allowing the computation of X-ray luminosities accurate to approximately 10% or better. For the first time large samples containing hundreds and thousands of X-ray bright stars will become available allowing an assessment of the high-luminosity tail of the distribution functions that is relevant for any quantitative assessment of the X-ray source counts. Furthermore, systematic studies of young stars in the general field will become possible, where they have dispersed from the birth regions. In the framework of this funding application we ask for support to carry out an effort to extract the stellar content of the ROSAT all-sky survey and the XMM-Newton slew survey using existing high-precision stellar catalogs and the upcoming Gaia data in terms of photometry and parallaxes. With these inputs we expect to identify the stellar population in these X-ray surveys with high accuracy and reliability and will use the results to compute accurate X-ray luminosity functions, space densities of active stars and identify the post T Tauri population of young stars in the field.