Wolf-Rayet wind structure and optical variability

Results are presented on the expected variability of Wolf-Rayet (WR) stars in broad-band optical polarimetry and photometry, and in emission line profiles, due to an inhomogeneous random distribution of blobs in spherical geometry. Time dependent 3 - D simulations are carried out with blob ejection random in time and direction, and the radiation properties are evaluated in the optically thin limit. In contrast with previous purely statistical analyses, inclusion in the present treatment of a beta velocity law and stellar occultation effects can yield results consistent with observations of the mean polarisation (p) over bar and the ratio R = sigma(p)/sigma(phot) Of polarimetric to photometric variability. Such consistency puts constraints on model parameters. Indeed by considering combinations of the three observables sigma(p), sigma(phot) and (p) over bar it is possible to infer reasonably good estimates of three wind-blob parameters - the beta of their velocity law, the total mass loss rate M in blobs and the total number N of blobs emitted per wind flow time (R-*/upsilon(infinity)), provided the blobs are reasonably localised in angular and radial extent. It is found that typical data requires beta greater than or equal to 1.5, N approximate to 20-50 and M approximate to 10(-4) M./year. The N estimate is consistent with the number of observed narrow features on emission lines. Smaller values of beta are excluded. This improved model shows that data do not after ail demand very dense blobs as previously suggested, and offers a valuable diagnostic of WR wind structure parameters.