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arXiv · 2601.21788

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

C. J. K. Larkin·J. Mackey·H. Jin·A. A. C. Sander·B. Reville·K. Anastasopoulou·M. Andersen·A. Bayo·J. J. Drake·E. K. Grebel·M. G. Guarcello·T. J. Haworth·V. M. Kalari·R. R. Lefever·F. Najarro·B. W. Ritchie·E. Sabbi
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Abstract

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 kyr 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.

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C. J. K. Larkin, J. Mackey, H. Jin, A. A. C. Sander, B. Reville, K. Anastasopoulou, M. Andersen, A. Bayo, J. J. Drake, E. K. Grebel, M. G. Guarcello, T. J. Haworth, V. M. Kalari, R. R. Lefever, F. Najarro, B. W. Ritchie, E. Sabbi. 2026-01-29. EWOCS-V: Is Wd1-72 a recent post-interaction WR+O binary?. https://doi.org/10.1051/0004-6361%2F202659205

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