Knowing the dancer from the dance: Line polarization simulations of colliding-wind binaries

Massive binary systems most likely play pivotal roles in producing energetic phenomena such as stripped-envelope supernovae, gamma-ray bursts, and compact mergers. However, the complex wind interactions in such systems are yet not well enough understood to test stellar evolution theories or establish connections between the characteristics of massive binaries and those of their potential descendants. Our group is pioneering the use of spectropolarimetric analysis of WR+O binaries to probe their complex wind collision structures and thereby diagnose the mass loss and mass transfer properties that determine their future evolution. However, because the scattering regions that produce polarization in these systems are highly asymmetric and change their orientation over the course of the orbital cycle, interpreting the observed time-dependent line polarization behavior is highly nontrivial. To aid in this interpretation, we have developed a version of the 3-D Monte Carlo radiative transfer code SLIP that specifically treats binary systems with completely asymmetric circumstellar material (CSM) configurations viewed at arbitrary inclination angles. The binary code considers multiple scattering effects, eclipses and occultations, and both stellar and non-stellar emission sources to allow for differing line and continuum polarization behavior. We present initial results from this code, which represent the first quantitative models of time-variable integrated line polarization in WR binary systems. Investigating the range of line polarization behavior produced by various configurations of emission and scattering material will not only illuminate the nature of the WR+O binaries for which we have spectropolarimetric data, but also light the path toward a larger-scale analysis of the wind and CSM structures in a variety of interacting binary systems.