Accreting Binary Eccentricities follow Predicted Equilibrium Values

TL;DR

This study examines circumbinary disks to find evidence of a predicted equilibrium eccentricity, revealing that actively accreting systems align with theoretical predictions, unlike the broader stellar binary population.

Contribution

It provides observational evidence supporting the existence of a predicted equilibrium eccentricity in actively accreting binary systems, linking theory with specific observed cases.

Findings

Actively accreting binaries follow the predicted eccentricity curve.

No preferred eccentricity in the overall stellar binary population.

Alignment with the disk is crucial for the observed eccentricity behavior.

Abstract

We investigate observations of circumbinary disks (CBD), to find evidence for an equilibrium eccentricity predicted by current binary accretion theory. Although stellar binary demographics in the Milky Way show no evidence for a preferred eccentricity for binary systems, we show that actively accreting systems lie on a predicted equilibrium eccentricity curve. We constrain our sample to only systems that have well defined orbital parameters (e.g,. eccentricity, mass-ratio, inclination angle). We find observations are consistent with theory for stellar binaries that are aligned with the disk and that are separated enough that tidal circularization is negligible. This suggests that eccentricity in these systems evolves after the dissipation of the CBD, given the flat eccentricity distribution of binary systems in the Milky Way.