3D models of radiatively driven colliding winds in massive O+O star binaries - I. Hydrodynamics

The dynamics of the wind-wind collision in massive stellar binaries are investigated using 3D hydrodynamical models which incorporate gravity, the driving of the winds, the orbital motion of the stars and radiative cooling of the shocked plasma. In this first paper, we restrict our study to main-sequence O+O binaries. The nature of the wind-wind collision region is highly dependent on the degree of cooling of the shocked plasma, and the ratio of the flow time-scale of the shocked plasma to the orbital time-scale. The pre-shock wind speeds are lower in close systems as the winds collide prior to their acceleration to terminal speeds. Radiative inhibition may also reduce the pre-shock wind speeds. Together, these effects can lead to rapid cooling of the post-shock gas. Radiative inhibition is less important in wider systems, where the winds are accelerated to higher speeds before they collide, and the resulting collision region can be largely adiabatic. In systems with eccentric orbits, cold gas formed during periastron passage can persist even at apastron, before being ablated and mixed into its surroundings and/or accelerated out of the system.