Spectropolarimetry of the WR+O binary gamma(2) Velorum during periastron passage

We present low-resolution (similar to 6 Angstrom) high Signal-to-noise spec tropolarimetric observations obtained with the new William-Wehlau spectropo larimeter for the apparently brightest Wolf-Rayet star in the sky, the 78.5 day WR + O binary gamma(2) Velorum. Quasi-simultaneous monitoring of all f our Stokes parameters I(lambda), q(lambda), u(lambda), and upsilon(lambda) was carried out over an interval of 31 nights centered on periastron. All e mission lines in our observed wavelength interval (5200-6000 Angstrom) show highly stochastic variations over the whole run. The phase-dependent behav ior of the excess emission in the C III lambda 5696 line can be related to the wind-wind collision phenomenon. Varying features of Stokes q and u are seen across the strong lines, probably as a result of variable electron sca ttering of mainly continuum light. The spherical symmetry of the WR wind is thus broken by the presence of the O companion and clumping in the WR wind . Similar features in the extended red wing of the C III 15696 emission lin e remain unexplained. No obvious circular line polarization features are se en across any emission line above the 3 sigma similar to 0.03% instrumental level.