X-ray emission from Lindroos binary systems

We present a study of the X-ray emission from binary systems extracted from the Lindroos catalogue (Lindroos 1986) based on the ROSAT All-Sky survey a s well as ROSAT PSPC and HRI pointings. The studied sample consists of visu al binary systems comprised of early-type primaries and late-type secondari es. The ages of the systems were determined by Lindroos (1985) from uvby be ta photometry of the primaries. These ages range between 33 and 135 Myr, so if the late-type secondaries are physically bound to the early-type primar ies, they could be Post-T Tauri stars (PTTS). We have found strong X-ray emission from several secondaries. This fact tog ether with their optical and IR data, make them bona fide PTTS candidates. We have also detected X-ray emission from several early-type primaries and, in particular, from most of the late-B type stars. Because their HRI hardn ess ratios are similar to these from resolved late-type stars, the presence of an unresolved late-type companion seems to be the cause of this emissio n.