Polarization variability among Wolf-Rayet stars. V - Linear polarization of the bright Cygnus stars and an anticorrelation of variability with wind speed

Abstract

This paper presents polarimetric data for seven of the eight bright WR stars in Cygnus. Six of the stars show only random, low-amplitude modulation on time scales of hours to days. One of these behaves as expected for a long-period WR + O system with an elliptical orbit. The eighth star is the only short-period WR + O binary in the sample. It is confirmed that the degree of random, intrinsic scatter in polarization is correlated with spectral subclass and terminal wind velocity. It is suggested that this is caused by the presence of propagating blobs which form, survive, and/or grow more easily in slower winds. Two models are proposed to explain the origin of the blobs.