Published online by Cambridge University Press: 26 May 2016
Massive stars in binary systems can generate X-ray emission in the region between the two stars where stellar winds collide. Colliding wind X-ray emission acts as an in-situ probe of important wind parameters like mass-loss rates, chemical abundances, wind velocities, and possibly magnetic field strengths. Variations in observed colliding-wind X-ray emission can be produced by the changing line-of-sight to the colliding wind region as the stars move in orbit and/or the changing emission measure of the shocked gas in the wind collision zone produced if the separations between the two stars change. X-ray variability depends on the wind and orbital parameters and so can in principal allow the direct measurement of mass functions even for low inclination systems and provide a connection between the stellar and wind parameters. X-ray emission from colliding wind systems can thus be used to refine our understanding of the evolutionary state of massive stars and to help test evolutionary models. We discuss recent advances in defining the X-ray spectral and temporal signatures of colliding wind X-ray emission using ROSAT, ASCA, RXTE, Chandra and XMM-Newton data.