HD 45166: The first magnetic Wolf-Rayet star

The mysterious "quasi Wolf-Rayet (qWR)" binary HD 45166 has been the subject of dozens of studies for over a century. It was proposed to consist of a 4Msun helium star with a Wolf-Rayet spectrum orbiting a B7 V star on a 1.6d period, making it the only intermediate-mass helium star known in the Galaxy. The properties of this binary are fully at odds with our understanding of wind-launching physics and binary evolution. However, spectropolarimetry obtained with the ESPaDOnS instrument in February 2022 reveal that the  qWR component exhibits the strongest magnetic field ever detected in the massive-star regime, amounting to 43kG. The detection makes this object the first known magnetic Wolf-Rayet star and a prime progenitor of a magnetar. A long-term monitoring campaign further implies that the true orbital period is of the order of tens of years, and not 1.6d. In my talk, I will present our spectroscopic and spectropolarimetric campaign, which reshuffles our understanding of this system. I will highlighting the implications of this object on our understanding of binary evolution and mergers, and conclude with a few ideas regarding the formation of such a unique object and other related objects in our Galaxy.