Clumping and mass loss in hot star winds

Abstract

We construct a simple model for the continuum free-free or subordinateline emission from Wolf-Rayet star winds, in which full-scale,compressible, supersonic turbulence is assumed to prevail. Based onobserved properties of the turbulent eddies with extrapolation byanalogy with Giant Molecular Clouds, such clumpy winds could lead to adecrease in the estimate of the mass-loss rate by a factor approximatelygreater than 3 compared to homogeneous winds of the same free-free orsubordinate line flux. Clumping may be important in all hot stars withwinds. In the particular case of the key eclipsing WR + O binary V444Cygni, the observed difference between the higher values of dot-Mtraditionally found from the radio free-free emission or therecombination flux of He I 1.08 micrometers assuming homogeneity, andthe lower dot-M values from dynamical arguments or polarimetry is foundto be a factor approximately greater than 3, in agreement with the aboveturbulence-based factor. The former methods depend on the square of thedensity and hence are sensitive to clumping effects, while the lattermethods are impervious to density fluctuations and are considered morereliable.