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

Type Journal Article
Names Qing-Kang Li, Joseph P. Cassinelli, John C. Brown, Richard Ignace
Publication Research in Astronomy and Astrophysics
Volume 9
Issue 5
Pages 558-576
Date May 1, 2009
URL http://adsabs.harvard.edu/abs/2009RAA.....9..558L
Library Catalog NASA ADS
Abstract 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 β velocity law and stellar occultation effects. We again search for parameters that can yield results consistent with observations in regards to the mean polarization bar p, the ratio R = σP/σphot of polarimetric to photometric variability and the volume filling factor fv. 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 β index, and the angular size of clumps is assumed to be fixed. By fitting the observed σP/σphot and the volume filling factor fv, clump velocity law index β (~ 2) and clump ejection rate N (~ 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.
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