Emission lines in scattered light map mass flows in Wolf-Rayet binaries

Companion interactions play a key role in shaping the fate of Wolf-Rayet (WR) stars in binary systems, as the mass lost from a WR star in its late evolutionary stages determines what type of explosive phenomenon may mark its death. But tracing the flow of mass between and around the stars is a difficult observational task in systems whose colliding winds obscure the stellar surfaces and produce complicated spectral signatures.

The technique of spectropolarimetry is uniquely well suited to studying complex geometrical systems because it disentangles spectral components that take different scattering paths through a complex distribution of circumstellar material. In a WR binary, the rotation of the system provides additional constraints by illuminating the winds and other mass flows from different perspectives. Analyzing the resulting variable emission line polarization variations provides constraints on the distribution, composition, density, and temperature of the gaseous structures in the system.

I will present an overview of my group’s ongoing project to carry out spectropolarimetric monitoring of 18 WR+O binaries using the RSS instrument on the Southern African Large Telescope. We use radiative transfer simulations to analyze the time- and wavelength-dependent data and reconstruct the 3-D characteristics of the mass flows in these systems. Accurately characterizing these structures is key to understanding the evolution of WR+O binaries and properly accounting for their contribution to the supernova (and possible GRB) progenitor population.