Radio emission from galactic Wolf-Rayet stars and the structure of Wolf-Rayet winds

Abstract

The authors have observed 23 Wolf-Rayet stars with the VLA at 6 cm and reobserved four stars at both 2 and 6 cm. When combined with previous data, these observations form an essentially complete sample of 40 W-R stars within a distance of 3 kpc and north of declination -47°. Available measurements of optical emission lines are used to estimate the volume emission measure, ionization balance, and terminal velocity V of the stellar wind for the sample stars. In the sample 33 stars (77%) are probable or definite thermal wind sources and five stars (12%) are probable or definite nonthermal sources. Stellar mass loss rates for the thermal sources lie in the narrow range 0.8×10<SUP>-5</SUP> ⪉ M⪉ 8.0×10<SUP>-5</SUP>M_sun;yr<SUP>-1</SUP>, with a mean value of 2×10<SUP>-5</SUP>M_sun;yr<SUP>-1</SUP>. It is speculated that the narrow range in observed Mis caused by a narrow range in intrinsic mass for the sample stars.