Line polarization modeling of WR binary systems

More than half of all massive stars form and evolve in binary systems, so understanding massive binary systems is essential to our understanding of their evolution and fates. Some massive stars evolve to the Wolf-Rayet stage, classically characterized by strong emission lines that indicate high-velocity ionized winds. Stars that reach this stage are linked to supernovae that may produce gamma-ray bursts, poorly understood high-energy events. In a massive binary system, these winds collide with the companion’s winds, producing wind geometry that enable us to learn more about the winds of both stars in the system. Polarization observations are the best method for detecting asymmetric scattering regions in unresolved systems, and spectropolarimetry is especially useful for WR stars given their stratified winds. However, interpreting the observations is difficult without modeling.

I have developed a Monte Carlo radiative transfer code that simulates the polarized light from massive stars in binary systems. I validated the model by investigating the mass-loss rate and wind structure of V444 Cyg, a well-studied WR + O binary system, and recovered results in agreement with previous studies. Uniquely, I used the code to simulate the polarization produced by line emission in the system. The model predicts significantly different polarization behavior with orbital phase for line polarization as compared to continuum polarization. I present preliminary comparisons of the model with V444 Cyg and other WR binary systems with spectropolarimetric data.