ABSTRACT. In this paper we present unfiltered and multiband (i.e., UBVRI) polarimetric observations of the short-period Wolf-Rayet binary CQ Cep. Using the basic assumptions of an optically thin, corotating envelope and pointlike sources (i.e., BME78 assumptions), we determined the orbital parameters of the system (i.e., i = 99° ± 1° and Ω = 76° ± 2° at the 2 σ level) with an accuracy many times better than any previous work. Residual non-BME78 variability around phase 0.0 was present in our data, which we associate with the polarimetric eclipse of the dense central parts of the Wolf-Rayet (W-R) wind by the orbiting O star. We attribute the observed phase lag of -0.15 between our residuals and those expected for a standard polarimetric eclipse to a wind-wind interaction (WWI) region distorted by Coriolis forces using the model presented by Marchenko et al. This model was also able to explain the strong wavelength dependence of the polarimetric amplitudes in our multiband observations. Our analysis also reveals important epoch-dependent departures of the matter distribution from spherical symmetry that were not related to the orbital plane and therefore cannot be the result of tidal interaction. We conclude that binarity is not playing an important role in driving the wind of the W-R star in CQ Cep and contributing to the observed nonspherical matter distribution. On the other hand, this asymmetry could be explained by a rotationally induced disk misaligned with the orbital plane.

Subject headings: binaries: eclipsing; polarization; stars: individual (CQ Cephei); stars: mass loss; stars: Wolf-Rayet; techniques: polarimetric

Print publication: Issue 2 (2005 April 20)
Received 2004 December 1, accepted for publication 2005 January 12