An Extreme Case of a Misaligned Highly Flattened Wind in the Wolf‐Rayet Binary CX Cephei

CX Cep (WR 151) is the WR+O binary (WN5+O5V) with the second shortest periodknown in our Galaxy. To examine the circumstellar matter distribution and tobetter constraint the orbital parameters and mass-loss rate of the WR star, weobtained broadband and multi-band (i.e. UBVRI) linear polarization observationsof the system. Our analysis of the phase-locked polarimetric modulationconfirms the high orbital inclination of the system (i.e. $i=65^o$). Using theorbital solution of Lewis et al. (1993) we obtain masses of $33.9 M_{\odot}$and $23.9 M_{\odot}$ for the O and WR stars respectively, which agree withtheir spectral types. A simple polarimetric model accounting for finite stellarsize effects allowed us to derive a mass-loss rate for the WR star of$0.3-0.5\times10^{-5} M_{\odot}/yr$. This result was remarkably independent ofthe model's input parameters and favors an earlier spectral type for the WRcomponent (i.e. WN4). Finally, using our multi-band observations, we fitted andsubtracted from our data the interstellar polarization. The resulting constantintrinsic polarization of $3-4%$ is misaligned in relation to the orbital plane(i.e. $\theta_{CIP}=26^o$ vs. $\Omega=75^o$) and is the highest intrinsicpolarization ever observed for a WR star. This misalignment points towards arotational (or magnetic) origin for the asymmetry and contradicts the mostrecent evolutionary models for massive stars (Meynet & Maeder 2003) whichpredict spherically symmetric winds during the WR phase (i.e. $CIP=0%$).Comment: 26 pages, 4 figures. Astrophysical Journal (submited