Eccentricity distribution of wide binaries

TL;DR

This study analyzes the eccentricity distribution of wide binaries within 67 parsecs, revealing an average eccentricity of 0.59, with differences observed in systems containing subsystems and a possible increase in eccentricity with orbital period.

Contribution

Introduces a new statistical method to determine eccentricity distributions of wide binaries from limited orbital data, accounting for observational biases and subsystem effects.

Findings

Average eccentricity of wide binaries is 0.59±0.02.

Systems with inner subsystems have lower average eccentricity (~0.52).

Eccentricity tends to increase with orbital period.

Abstract

A sample of 477 solar-type binaries within 67pc with projected separations larger than 50AU is studied by a new statistical method. Speed and direction of the relative motion are determined from the short observed arcs or known orbits, and their joint distribution is compared to the numerical simulations. By inverting the observed distribution with the help of simulations, we find that average eccentricity of wide binaries is 0.59+-0.02 and the eccentricity distribution can be modeled as f(e) ~= 1.2 e + 0.4. However, wide binaries containing inner subsystems, i.e. triple or higher-order multiples, have significantly smaller eccentricities with the average e = 0.52+-0.05 and the peak at e ~ 0.5. We find that the catalog of visual orbits is strongly biased against large eccentricities. A marginal evidence of eccentricity increasing with separation (or period) is found for this sample. Comparison with spectroscopic binaries proves the reality of the controversial period-eccentricity relation. The average eccentricity does increase with binary period, being 0.39 for periods from 10^2 to 10^3 days and 0.59 for the binaries studied here (10^5 to 10^6 days).