Theory of thermal and ionization effects in colliding winds of WR+O binaries

The colliding winds interaction zone in WR+O binaries is a highly complex environment. In this review we summarize the progress made towards its theoretical understanding during the last years. We review the effect of different physical processes on the interaction zone, among them geometry and orbital motion, radiative forces, thermal conduction, instabilities and turbulence, ionizing radiation, dust formation, clumped winds, magnetic fields, and particle acceleration. Implications with regard to observations are discussed. Subsequently we proceed to the important question of mutual interaction amongst these processes. Because of the wealth of physical processes involved, numerical simulations are usually mandatory. Finally, we turn to the combined role these processes play for the thermal and ionization properties of the colliding winds interaction zone in WR+O binaries.