Binary-induced spiral arms inside the disc cavity of AB Aurigae

TL;DR

This study shows that a binary star within the dust cavity of AB Aurigae can generate the observed spiral arms, with specific orbital parameters matching the gas emission data and predicting observable companion motion.

Contribution

We demonstrate that a binary star inside the disc cavity can produce the observed spiral structures, providing constraints on its properties and future observational signatures.

Findings

Binary companion with specific orbital parameters reproduces observed spirals.

Predicted location and motion of the companion can be tested observationally.

Spiral structure varies over time due to binary inclination.

Abstract

In this work we demonstrate that the inner spiral structure observed in AB Aurigae can be created by a binary star orbiting inside the dust cavity. We find that a companion with a mass-ratio of 0.25, semi-major axis of 40 au, eccentricity of 0.5, and inclination of 90{\deg} produces gaseous spirals closely matching the ones observed in $^{12}$CO (2-1) line emission. Based on dust dynamics in circumbinary discs (Poblete, Cuello, and Cuadra 2019), we constrain the inclination of the binary with respect to the circumbinary disc to range between 60{\deg} and 90{\deg}. We predict that the stellar companion is located roughly 0.18 arcsec from the central star towards the east-southeast, above the plane of the disc. Should this companion be detected in the near future, our model indicates that it should be moving away from the primary star at a rate of 6 mas/yr on the plane of the sky. Since our companion is inclined, we also predict that the spiral structure will appear to change with time, and not simply co-rotate with the companion.