Visual binary stars with known orbits in Gaia EDR3

TL;DR

This study validates Gaia EDR3 parallaxes for visual binary stars, identifies issues with parallax accuracy, and estimates stellar masses using combined astrometric data and mass-luminosity relations.

Contribution

It provides a comprehensive validation of Gaia EDR3 parallaxes for binary systems and introduces methods to improve astrometric data and mass estimates.

Findings

Two-thirds of binaries with 0.2-0.5 arcsec separation lack Gaia parallax solutions.

Gaia EDR3 parallax errors are underestimated by at least a factor of 3 for some sources.

Distant companions and proper motion analysis reveal unreliable Gaia parallaxes in certain cases.

Abstract

3350 objects from the Sixth catalog of orbits of visual binary stars (ORB6) are investigated to validate Gaia EDR3 parallaxes and provide mass estimates for the systems. We show that 2/3 of binaries with 0.2 - 0.5 arcsec separation are left without a parallax solution in EDR3. A special attention is paid to 521 pairs with parallax known separately for both components. We find 16 entries that are deemed to be chance alignments of unrelated stars. At once we show examples of high-confidence binary systems with significant differences in the reported parallaxes of their components. Next we conclude that the reported Gaia EDR3 parallax errors are underestimated, at least by a factor of 3 for sources with large RUWE. Parallaxes are needed to estimate stellar masses. Since nearly 30\% of ORB6 entries lack 5 or 6-parameter solution in EDR3, we attempt to enrich the astrometric data. Distant companions of ORB6 entries are revealed in EDR3 by analysis of stellar proper motions and Hipparcos parallaxes. Notably, in 28 cases intrinsic EDR3 parallaxes of the binary components appear to be less reliable than the parallax of the outer companions. Gaia DR2, TGAS and Hipparcos parallaxes are used when EDR3 data is unavailable. Synthetic mass-luminosity relation in the G band for main sequence stars is obtained to provide mass estimates along with dynamical masses calculated via Kepler's Third Law.