Parallax zeropoint and uncertainty model for Gaia DR3 astrometric binary solutions

Establish the parallax zeropoint and develop a validated uncertainty model for the Gaia DR3 12-parameter astrometric binary solutions (Orbital and AstroSpectroSB1), beyond purely statistical errors, to ensure robust inferences when combining astrometry with radial-velocity data.

Background

When comparing their joint Gaia+RV fits to Gaia-only constraints, the authors note generally good agreement but caution that the uncertainties used are purely statistical. Accurate parallax zeropoints and error models specific to the non-single-star solutions are essential for precise mass and orbit inference.

This calibration is particularly important because small systematic errors in parallax or its uncertainty can significantly affect companion-mass inferences for compact-object candidates near the Chandrasekhar mass.