MODELING OF X-RAY-EMISSION FROM WR+O BINARY-SYSTEMS

Two-dimensional calculations of colliding stellar winds are performed for the case of a WR + O binary system. The effects of energy losses by free-free emission and Comptonization as well as those of stellar wind acceleration are considered. The results show that the interaction region must be a powerful X-ray source. The main dimensional parameters determining the X-ray spectrum and the luminosity of a WR + O binary system are the stellar mass losses, the wind velocities, the separation between the stars and their chemical composition (the X-ray emission characteristics of WN + O and WC + O systems are very different). An investigation of energy losses due to free-free emission shows that radiative losses may play an important role in the physics of the interaction region if all the thermal processes are included (free-free, two-photon and recombination continua, and emission lines). In this case, the thermal conductivity must be taken into account in the modelling of colliding stellar winds. The closer the binary system, the more important is the role of energy losses by thermal emission and Comptonization. The effects of stellar wind acceleration are also important for close WR + O binary systems in which the contribution of the shocked O-star wind gas to the total X-ray emission may be dominant.