Probing Colliding Wind Binaries with High-Resolution X-ray Spectra

X-ray line profiles represent a new way of studying the winds of massive stars. In particular, they enable us to probe in detail the wind-wind collision in colliding wind binaries, providing new insights into the structure and dynamics of the X-ray-emitting regions. We present the key results of new analysis of high-resolution Chandra X-ray spectra of two important colliding wind systems, Velorum and WR140. The lines of Vel are essentially unshifted from their rest wavelengths, which we suggest is evidence of a wide shock opening angle, indicative of sudden radiative braking. The widths of the lines of WR140 are correlated with ionization potential, implying nonequilibrium ionization. The implications of these results for the radio emission from these systems are discussed, as are some of the future directions for X-ray line profile modeling of colliding wind binaries.