Blobs in Wolf‐Rayet Winds: Random Photometric and Polarimetric Variability

Some isolated Wolf-Rayet stars present random variability in their opticalflux and polarization. We make the assumption that such variability is causedby the presence of regions of enhanced density, i.e. blobs, in their envelopes.In order to find the physical characteristics of such regions we have modeledthe stellar emission using a Monte Carlo code to treat the radiative transferin an inhomogeneous electron scattering envelope. We are able to treat multiplescattering in the regions of enhanced density as well as in the envelopeitself. The finite sizes of the source and structures in the wind are alsotaken into account. Most of the results presented here are based on a parameterstudy of models with a single blob. The effects due to multiple blobs in theenvelope are considered to a more limited extent. Our simulations indicate thatthe density enhancements must have a large geometric cross section in order toproduce the observed photopolarimetric variability. The sizes must be of theorder of one stellar radius and the blobs must be located near the base of theenvelope. These sizes are the same inferred from the widths of the sub-peaks inoptical emission lines of Wolf-Rayet stars. Other early-type stars show randompolarimetric fluctuations with characteristics similar to those observed inWolf-Rayet stars, which may also be interpreted in terms of a clumpy wind.Although the origin of such structures is still unclear, the same mechanism maybe working in different types of hot stars envelopes to produce suchinhomogeneities.Comment: Accepted to ApJ. 17 pages + 6 figure