Driving asymmetric red supergiant winds with binary interactions

Abstract

ABSTRACT Massive stars in the red supergiant (RSG) phase are known to undergo strong mass-loss through winds and observations indicate that a substantial part of this mass-loss could be driven by localized and episodic outflows. Various mechanisms have been considered to explain this type of mass-loss in RSGs, but these models often focus on single-star evolution. However, massive stars commonly evolve in binary systems, potentially interacting with their companions. Motivated by observations of the highly asymmetric circumstellar ejecta around the RSG VY CMa, we investigate a scenario where a companion on an eccentric orbit grazes the surface of an RSG at periastron. The companion ejects part of the outer RSG envelope, which radiatively cools, reaching the proper conditions for dust condensation and eventually giving rise to dust-driven winds. Using simple treatments for radiative cooling and dust-driven winds, we perform three-dimensional smoothed particle hydrodynamic simulations of this scenario with a $20\, {\rm M}_\odot$ RSG and a $2\, {\rm M}_\odot$ companion. We follow the evolution of the binary throughout a total of 14 orbits and observe that the orbit tightens after each interaction, in turn enhancing the mass-loss of subsequent interactions. We show that one such grazing interaction yields outflows of $3\times 10^{-4}\, {\rm M}_\odot$, which later results in wide asymmetric dusty ejecta, carrying a total mass of $0.185\, {\rm M}_\odot$ by the end of simulations. We discuss the implications for the evolution of the binary, potential observational signatures, as well as future improvements of the model required to provide sensible predictions for the evolution of massive binaries.