2006ApJ...640..995V

CX Cep (WR 151) is the WR+O binary (WN5+O5 V) with the second shortest period known in our Galaxy. To examine the circumstellar matter distribution and to better constraint the orbital parameters and mass-loss rate of the W-R star, we obtained broadband and multiband (i.e., UBVRI) linear polarization observations of the system. Our analysis of the phase-locked polarimetric modulation confirms the high orbital inclination of the system (i.e., i=65°). Using the orbital solution of Lewis et al. ((ref???)1993), we obtain masses of 33.9 and 23.9 M_☉for the O and W-R stars, respectively, which agree with their spectral types. A simple polarimetric model accounting for finite stellar size effects allowed us to derive a mass-loss rate for the W-R star of 0.3-0.5x10^–5 M_☉/yr. This result was remarkably independent of the model's input parameters and favors an earlier spectral type for the W-R component (i.e., WN4). Finally, using our multiband observations, we fitted and subtracted from our data the interstellar polarization. The resulting constant intrinsic polarization of 3%-4% is misaligned in relation to the orbital plane (i.e., θ_CIP=26° vs. Ω=75°) and is the highest intrinsic polarization ever observed for a W-R star. This misalignment points toward a rotational (or magnetic) origin for the asymmetry and contradicts the most recent evolutionary models for massive stars (Meynet & Maeder (ref???)2003) that predict spherically symmetric winds during the W-R phase (i.e., CIP=0%).