Radio and infrared structure of the colliding-wind Wolf-Rayet system WR147

Abstract

New, high-resolution infrared and radio images of the X-ray-Iuminous Wolf-Rayet system WR 147 (AS 431) are presented. The 5-GHz radio image resolves both components of this double source. The emission from one component, that to the south and associated with the wind of the WN8 star, has an extent of -170 x 253 mas 2 , indicating that the stellar wind is not spherically symmetric. The second, non-thermal component -0.6 arc sec north of the WN8 star is extended east-west to -267 mas. The infrared image reveals the presence of a companion to the WN8 star, close to the non-thermal radio source but slightly (-60 mas) more distant from the WN8 star. The companion is t::.K -3 mag fainter than the WN8 star and has a luminosity of a BO.5V star, just sufficiently luminous to possess a stellar wind capable of colliding with that of the WN8 star. The presence of the non-thermal emission between the two stars and much closer to that with the weaker wind is direct evidence for a colliding-wind origin for the emission. A significant portion of the X -ray emission can also be accounted for by the release of energy in the wind collision. Comparison of the non-thermal flux with those of the three systems incorporating WC-type stars (WR 125, WR 140 and WR 146) shows a correlation with velocity of the WR wind.