Two-epoch orbit estimation for wide binaries resolved in Hipparcos and Gaia

TL;DR

This paper presents a method to estimate orbital parameters of wide binary stars using data from Hipparcos and Gaia, demonstrating potential for improved orbital solutions with future astrometry missions.

Contribution

The paper introduces a novel two-epoch orbit estimation technique leveraging data from Hipparcos and Gaia, enhancing analysis of wide binaries with 25-year epoch separation.

Findings

Useful orbital estimates possible for binaries with periods up to ~500 years.

Method's accuracy limited by Hipparcos data quality and multiple system perturbations.

Future missions like Gaia-NIR and Theia can significantly improve results.

Abstract

The Hipparcos catalog and its Double and Multiple System Annex (DMSA) lists 4099 components with individual proper motions and coordinates on the epoch 1991.25. Many of these long-period binary stars are also present in the Gaia Data Release 2 (DR2). Using the available relative positions and proper motions separated by 25.25 years, the equations of relative orbital motion can be solved for the two epoch eccentric anomalies, orbital period, and eccentricity. The method employs elimination of the linear Thiele-Innes unknowns and nonlinear optimization of the remaining condition equations. The quality of these solutions is compromised by the insufficient condition and modest precision of the Hipparcos astrometric data, as revealed by Monte-Carlo simulations with artificially perturbed data points. The presence of multiple systems and optical pairs can also perturb the results. Limited experiments with artificial data indicate that useful estimates can be obtained with a 25-year epoch difference for wide binaries with orbital periods up to $\sim 500$ years. The prospects of this method dramatically improve with the proposed next-generation space astrometry missions such as Gaia-NIR and Theia, especially when additional conditions are included from astrometric or spectroscopic measurements. A ancillary catalog of cross-identification and astrometric information for 1295 double star pairs cross-matched in Gaia DR2 and Hipparcos is published.