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

Abstract

CX Cep (WR 151) is the WR+O binary (WN5+O5V) 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 WR star, we obtained broadband and multi-band (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. $i=65^o$). Using the orbital solution of Lewis et al. (1993) we obtain masses of $33.9M_{\odot }$ and $23.9M_{\odot }$ for the O and WR 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 WR star of $0.3-0.5\times 10^{-5}{M}_{\odot }/yr$. This result was remarkably independent of the model's input parameters and favors an earlier spectral type for the WR component (i.e. WN4). Finally, using our multi-band 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. ${\theta }_{CIP}=26^o$ vs. $\Omega =75^o$) and is the highest intrinsic polarization ever observed for a WR star. This misalignment points towards a rotational (or magnetic) origin for the asymmetry and contradicts the most recent evolutionary models for massive stars (Meynet & Maeder 2003) which predict spherically symmetric winds during the WR phase (i.e. $CIP=0$).

26 pages, 4 figures. Astrophysical Journal (submited)

References in corpus (4)

• A new calibration of stellar parameters of Galactic O stars
• The evolution of rotating stars
• Stellar evolution with rotation X: Wolf-Rayet star populations at solar metallicity
• 9286 Stars: An Agglomeration of Stellar Polarization Catalogs

Cited by in corpus (11)

• Physical Properties of Wolf-Rayet Stars
• On the role of the WNH phase in the evolution of very massive stars: Enabling the LBV instability with feedback
• Discovery of a magnetic field in the rapidly-rotating O-type secondary of the colliding-wind binary HD 47129 (Plaskett's star)
• A first orbital solution for the very massive 30 Dor main-sequence WN6h+O binary R145
• Constraining GRB progenitor models by probing Wolf-Rayet wind geometries in the Large Magellanic Cloud
• The spin rates and spin evolution of the O components in WR+O binaries
• Asymmetric Wolf-Rayet winds: implications for GRB afterglows
• Modeling Forbidden Line Emission Profiles from Colliding Wind Binaries
• A multi-wavelength search for intrinsic linear polarization in Wolf-Rayet winds
• Intrinsically Polarized Stars and Implication for Star Formation in the Central Parsec of Our Galaxy
• The circumstellar environment of rotating Wolf-Rayet Stars and the implications for GRB afterglows