The stellar content of medium and high sensitivity X-ray surveys

Synthesis stellar X-ray population models are powerful tools to predict and analyze the stellar content of X-ray surveys. Conversely X-ray observations can help to better constrain model parameters ill-defined from observations at other wavelength. In this paper, we first discuss the similarities and differences expected in the stellar content of low-medium (ROSAT) and high (XMM-Newton) sensitivity surveys as a function of galactic latitude. We also demonstrate how useful ROSAT and XMM pointings are to study young local features in the solar neighborhood. Finally we present ongoing work on synthetic X-ray luminosity functions in the ROSAT and XMM energy bands which aim at improving the modeling of the decay of X-ray activity with age and mass within stellar X-ray population model.