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

• Main Authors: Villar-Sbaffi, A, St-Louis, N, Moffat, Anthony F. J, Piirola, Vilppu, de Physique, 1- Departement, Vaticana, Observatoire du Mont Megantic. 2- Tuorla Observatory. 3- Specola
• Format: Journal Article
• Language: English
• Published: 26-07-2005
• Subjects: Physics - Astrophysics of Galaxies; Physics - Cosmology and Nongalactic Astrophysics; Physics - Earth and Planetary Astrophysics; Physics - High Energy Astrophysical Phenomena; Physics - Instrumentation and Methods for Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.astro-ph/0507616

Astrophys.J.640:995-1004,2006 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 $33.9 M_{\odot}$
and $23.9 M_{\odot}$ 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
$0.3-0.5\times10^{-5} M_{\odot}/yr$. 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. $CIP=0%$).