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

TL;DR

This study investigates the extreme brightness variations of the blue supergiant MACHO 80.7443.1718, revealing it as a wind-wind collision binary with enhanced mass loss likely driven by tidal interactions and rotation.

Contribution

It provides the first detailed analysis of MACHO 80.7443.1718 as a wind-wind collision binary, refining its orbital parameters and demonstrating the role of companion-driven processes in mass loss.

Findings

Confirmed MACHO 80.7443.1718 as a WWC binary system.

Estimated primary's mass-loss rate at 4.5×10⁻⁵ M☉/yr, exceeding theoretical predictions.

Identified evidence for a tertiary component and refined orbital parameters.

Abstract

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 may not be 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$_\odot\,{\rm yr}^{-1}$. We conclude that 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 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.