Exploring extreme brightness variations in blue supergiant MACHO 80.7443.1718: Evidence for companion-driven enhanced mass loss

Evolution of massive stars is dominated by interactions within binary systems. Therefore, it is necessary to investigate all forms of interaction in binary systems that may affect the evolution of the components. One of such `laboratories' is the massive eccentric binary system MACHO$\,$80.7443.1718 (ExtEV). We examine whether the light variability of the ExtEV can be explained by a wind-wind collision (WWC) binary system model. We conducted an analysis of broadband multi-color photometry of ExtEV, time-series space photometry from TESS, ground-based Johnson $UBV$ photometry, and time-series spectroscopy. We fitted an analytical model of light variations to the TESS light curve of ExtEV. We rule out the possibility of the presence of a disk around the primary component. We also argue that the non-linear wave-breaking scenario is not consistent with the observations of ExtEV. We refine the orbital parameters of ExtEV and find evidence for the presence of a tertiary component. Using evolutionary models we demonstrate that the primary component's mass is between 25 and 45$\,$M$_\odot$. We successfully reproduce light curve of ExtEV with our model, showing that the dominant processes shaping its light curve are atmospheric eclipse and light scattered in the WWC cone. We also estimate the primary's mass-loss rate due to stellar wind for $4.5\cdot 10^{-5}\,$M$_\odot\,{\rm yr}^{-1}$. ExtEV is not an extreme eccentric ellipsoidal variable, but 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. 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.

Comment: Submitted to Astronomy&Astrophysics, 23 pages, 15 figures, 9 tables