The eccentricity distribution of wide binaries

Abstract

ABSTRACT Future Gaia and Legacy Survey of Space and Time data releases, together with wide area spectroscopic surveys, will deliver large samples of resolved binary stars with phase space coordinates, albeit with low-cadence. Given an eccentricity law f(ϵ), we derive properties of (i) the velocity distribution $v/\sqrt{G M/r}$ normalized by the value for a circular orbit at the measured separation r; (ii) the astrometric acceleration distributions a/(GM/r2) again normalized to the circular orbit value. Our formulation yields analytic predictions for the full statistical distribution for some commonly used eccentricity laws, if the time-scale of data sampling is comparable to or exceeds the binary period. In particular, the velocity distribution for the linear eccentricity law is surprisingly simple. With Bayesian analysis, we suggest a method to infer the eccentricity distribution based on the measured velocity distribution.