EWOCS-V: Is Wd1-72 a recent post-interaction WR+O binary?

The evolutionary origin of Wolf-Rayet (WR) stars at solar metallicity is unclear. Single-star evolution from massive O stars, possibly via a luminous blue variable phase, is challenged by binary period distributions of different WR subtypes. Wd1-72 is a WN7b+O binary embedded in the collective wind of the Galactic young massive cluster Westerlund 1 (Wd 1). It is surrounded by highly structured nebulosity, with cometary tails pointing away from Wd 1 and quasi-spherical droplets towards it. In this Letter, we demonstrate that this morphology can be qualitatively reproduced by a hydrodynamic simulation of non-conservative Roche-lobe overflow (RLOF) mass loss into a cluster wind. Our model is based on a detailed binary evolution track consistent with key known properties of Wd1-72. Our work suggests Wd1-72 could be only ∼10 ̨yr post-RLOF, and the hydrogen-free nature of Wd1-72 favours this being a second or subsequent RLOF episode. Follow-up observations could make Wd1-72 a valuable benchmark for probing mass loss and mass transfer in forming gravitational-wave binary-progenitor systems.