Driving asymmetric red supergiants winds with binary interactions

TL;DR

This study explores how binary interactions, especially a grazing companion, can induce asymmetric winds and dust ejection in red supergiants, providing insights into observed asymmetries and mass loss mechanisms.

Contribution

It introduces a novel 3D simulation model showing how binary grazing interactions can drive asymmetric winds and dust formation in red supergiants.

Findings

Grazing binary interactions produce asymmetric dusty ejecta.

Orbit tightening enhances mass loss over time.

Simulated outflows match observed asymmetries in RSGs.

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 localised 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 a red supergiant 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 3D smoothed particle hydrodynamics simulations of this scenario with a $20\,M_\odot$ RSG and a $2\,M_\odot$ 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 $3\times10^{-4}\,M_\odot$, which later results in wide asymmetric dusty ejecta, carrying a total mass of $0.185\,M_\odot$ 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.