MACHO 80.7443.1718 UBV light curves

To derive the parameters of the primary component of the system, we fitted spectral energy distribution (SED) and calculated evolutionary models of massive stars that included mass loss. Using radial-velocity data, we determined the spectroscopic parameters of the system. We also fitted an analytical model of light variations to the TESS light curve of ExtEV.

The ExtEV system exhibits an infrared excess, indicating an increased mass- loss rate. The system does not match the characteristics of B[e] stars, however. We rule out the possibility of the presence of a Keplerian disk around the primary component.

We also argue that the scenario with periodic Roche-lobe overflow at periastron may not be consistent with the observations of ExtEV. Analysis of SED suggests that the primary component has a radius of about 30R_{sun}_ and a luminosity of ~6.6x10^5^L_{sun}_. With the analysis of the radial- velocity data, we refine the orbital parameters of ExtEV and find evidence for the presence of a tertiary component in the system.

Using evolutionary models we demonstrate that the primary component's mass is between 25 and 45M_{sun}_. We successfully reproduce the light curve of ExtEV with our analytical model, showing that the dominant processes shaping its light curve can be attributed to atmospheric eclipse and light scattered in the WWC cone. We also estimate the primary's mass-loss rate due to stellar wind for 4.5x10^-5^M_{sun}_/yr.

ExtEV is most likely not an extreme eccentric ellipsoidal variable, but rather an exceptional WWC binary system. The mass loss rate we derived exceeds theoretical predictions by up to two orders of magnitude. This implies that the wind in the system is likely enhanced by tidal interactions, rotation, and possibly also tidally excited oscillations.

Therefore, ExtEV represents a rare evolutionary phase of a binary system that may help to understand the role of a companion-driven enhanced mass loss in the evolution of massive binary systems.