Polarization variability among Wolf-Rayet stars. III - A new way to derive mass-loss rates for Wolf-Rayet stars in binary systems

Abstract

We present new results from the polarimetric monitoring of two W-R + O binaries (HD 186943 and HD 211853) and three suspected low-amplitude single-line binaries (HD 177230, 209 BAC, and HD 187282). From these and other data, we derive mass-loss rates (M) for ten W-R stars in massive binaries on the basis of the amplitude of the systematic phase-dependent modulation in linear polarization. The advantage over other independent methods of estimating the mass4oss rates lies in the relatively simple physics involved, i.e., polarization by scattering of companion-star light off free electrons in the strongly ionized interior region of the W-R wind. Neglecting possible systematic effects, the rates derived are estimated to be accurate typically to within ±40% where the mass-loss rates for particular stars have been determined by other means, our rates agree reasonably well with the rates obtained by the most reliable of these other means. True stellar masses can now be estimated from the orbital inclinations derived on the basis of the polarization data themselves. These lead to a correlation of M with the mass of the W-R star, as proposed by Abbott et al. 1986.