The Importance of Radiative Braking for the Wind Interaction in the Close WR+O Binary V444 Cygni

Abstract

We describe radiation-hydrodynamical simulations of the wind interaction in the close WR+O binary V444 Cygni, with special emphasis on the potential role of the O-star light in decelerating the approaching massive WR wind. We demonstrate that such radiative braking can significantly alter the strength and overall geometry of the wind interaction, leading, for example, to a substantially wider opening angle for the wind bow shock. It can also cause the X-ray production to fall far below previous theoretical estimates based on collision of the two winds at their terminal speeds. We further find that the importance of radiative braking in this system depends crucially on the effectiveness of the WR wind line opacity in reflecting O-star light. This suggests that observational estimates of quite gross system characteristics, like the bow-shock opening angle, can be used to infer the degree of radiative braking, and so provide a useful new contraint for line-driving models of WR winds.