X-RAY-EMISSION FROM COLLIDING WINDS IN PRE-MAIN-SEQUENCE BINARY-SYSTEMS

We present model calculations of the X-ray emission in the range 0.1-2.5 keV from colliding supersonic winds in young binary systems. For typical winds, with velocities between 300 and 500 km s(-1) and mass-loss rates between 10(-8) and 10(-6) M. yr(-1), we find that the X-ray luminosity of the interaction region amounts to 10(30)-10(33) erg s(-1) for binary separations less than 50 au. While the luminosity is in accordance with s the observed range for pre-main-sequence stars, the bulk of the emission occurs in the soft part of the spectrum below 1 keV. We have considered the effects of the interaction of winds with different velocities. In this case, the X-ray emission consists of a 'soft' component, due to the slower wind, and a 'hard' component from the fast one. Such a double-peaked spectrum is also found in the case where, in addition to the shocked emitting gas, a stellar component with typical temperature similar to 1 keV is present. Thus the soft X-ray excess represents the signature of interacting stars and can be used as an effective diagnostic to search for binary systems.