Resolving the heart of the Wolf-Rayet binary Apep with ALMA

The Wolf-Rayet (WR) phase is a critical stage in the evolution of massive stars. During this phase, stars experience a significant loss of mass in the form of fast winds that are enriched with heavy elements. There are only a few WR binaries in the Galaxy, with being a truly exceptional system that exhibits a bright colliding-wind region at radio wavelengths and an impressive dust plume in the infrared. Although the angular separation between the two components of the binary (WN and WC) has been indirectly inferred to be about 47 mas, it has yet to be confirmed through direct measurements. Apep We aim to image the system at millimetre wavelengths to determine the position of the WR stars and their mass-loss rates. Apep We observed with ALMA in Bands 6 and 7 in a large baseline configuration and we achieved an angular resolution of ≈20 mas. We used a canonical spherical wind model to convert the measured flux densities into wind mass-loss rates. Apep Towards , we detect point-like emission coming from the WN star and elongated emission most likely from the colliding-wind region; the WC star is not detected. We also detect the O star that has been associated with the system at an angular distance of 0.7$''$. Our analysis favours mass-loss rates for the WN and WC components of dot Apep M _ ∼ 2 _ WN -5 and dot M WC -5 respectively. The mass-loss rates of these WR stars are significantly lower than previously reported, and we examine several factors that may account for this discrepancy. The diffuse emission from the colliding-wind region cannot be accounted for by the synchrotron flux, and thus additional free--free or dust emission is present.