Program: GN-2021A-Q-406

We propose a comprehensive spectroscopic investigation of the long-period binaries WR125 and WR137. WR125 is a dust-producing WC binary, with a recently measured period of 28.1 years. It does not have any measured orbital elements at this time, and recent infrared photometry suggests that the system is near periastron. We expect that the eccentricity is about 0.8-0.9, making this an ideal time to study the system. We propose GMOS spectroscopy for kinematics, as well as GNIRS spectroscopy for understanding the colliding winds in the system. The better-studied WC binary WR137 is nearingg periastron, so we propose monitoring of it with GNIRS so that we can compare the colliding wind geometry of the systems with drastically different eccentricities. These measurements will facilitate modeling of the colliding winds in the systems, allowing us to probe the conditions under which dust can form in WC binaries, which could have formed the first dust in the Universe.