Stellar X-Ray surveys and Galaxy structure

Soft X-ray surveys are very effective to study low-mass stellar populations in our Galaxy. Indeed stellar X-ray counts well complement optical stellar counts since they allow us to study spatial distributions and densities of main sequence stars as function of age. This capability is due to the strong dependence of X-ray luminosity on stellar age, especially during the main sequence life. As a consequence X-ray surveys oversample young stars, detectable at large distances, permitting to study the spatial characteristics of these populations and the stellar birthrate in the solar neighborhood in the last billion year. In this context both low and high latitude X-ray surveys play an important role, since low-latitude surveys allow us to determine the stellar density as a function of age on the Plane, while high latitude surveys constrain the scale heights of the different populations. The comparison of the results at various latitudes can constrain the recent star formation history in the solar neighborhood. I will discuss which improvements the Chandra and XMM-Newton surveys can provide in our knowledge of stellar populations, and some preliminary results from new ongoing surveys.