Polarization variability arising from clumps in the winds of Wolf-Rayet stars

Polarimetric and photometric variability of Wolf-Rayet (WR) stars as caused by clumps in the winds is revisited. In our model, which is improved from Li et al., radial expansion of the thickness is accounted for, but we retain dependence on the beta velocity law and stellar occultation effects. We again search for parameters that can yield results consistent with observations in regards to the mean polarization (p) over bar, the ratio R = sigma(p)/sigma(phot) of polarimetric to photometric variability and the volume filling factor f(V). Clump generation and spatial distribution are randomized by the Monte Carlo method so as to produce clumps which are, in the mean, distributed uniformly in space and have time intervals that obey a Gaussian distribution. The generated clumps move radially outward with a velocity law determined by a beta index, and the angular size of clumps is assumed to be fixed. By fitting the observed sigma(p)/sigma(phot) and the volume filling factor f(V), clump velocity law index beta (similar to 2) and clump ejection rate beta (similar to 1) are inferred, and are found to be well constrained. In addition, the subpeak features of broad emission lines seem to support the clump ejection rate. Meanwhile, the fraction of total mass loss rate that is contained in clumps is obtained by fitting observed polarization. We conclude that this picture of the clumps' properties produces a valuable diagnostic of WR wind structure.