One Star, Two Star, Red Star, Blue Star: Probing the Binary Status of the Wolf-Rayet Stars WR 12 and WR 71 with Spectropolarimetry
Massive stars lose their mass through high stellar winds which create dense circumstellar structures of dust and gas around the star. The mass and angular momentum lost from the star shapes its future evolution. In the case of massive Wolf-Rayet (WR) stars, they may show periodic variability due to rotation or interaction with an O-star or compact companion. By studying how light is scattered in their stellar winds, through time-dependent polarimetry, we can begin to constrain the geometry and mass loss process of these systems. Our team obtained spectropolarimetric data from several southern hemisphere WR systems using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT). I analysed data pertaining to two of these systems, WR 12 and WR 71, whose binary status is not confirmed. I investigated the radial velocities of each WR star, as well as the time dependence of both continuum and line polarisation behaviour, including estimating interstellar polarisation (ISP) contributions, which have not been estimated before. The radial velocity calculations shed light on the current ephemerides for these two objects, suggesting that the ephemeris for WR 71 needs to be redefined. The continuum polarisation behaviour does not
follow the expected variations based on the generally-accepted BME model for either system. The integrated line polarisation values show evidence for an elongated outer wind structure
in WR 12 but not in WR 71, suggesting that the WR star in WR 12 may be a rapidly rotating potential gamma-ray burst progenitor. To better characterise the polarised emission line profiles, I developed a technique to assess the asymmetry of each profile. These results indicate large differences between emission lines of different ionic species, as well as between emission lines of same species between the two different targets. I discuss the implications of these findings in the context of the geometry and binary status of WR 12 and WR 71.