Validation of the Gaia Early Data Release 3 Parallax Zero-point Model with Asteroseismology

Gaia Early Data Release 3 (EDR3) provides trigonometric parallaxes for 1.5 billion stars, with reduced systematics compared to Gaia Data Release 2 and reported precisions better by up to a factor of 2. New to EDR3 is a tentative model for correcting the parallaxes of magnitude-, position-, and color-dependent systematics for five- and six-parameter astrometric solutions, Z(5) and Z(6). Using a sample of over 2000 first-ascent red giant branch stars with asteroseismic parallaxes, I perform an independent check of the Z(5) model in a Gaia magnitude range of 9 less than or similar to G less than or similar to 13 and color range of 1.4 mu m(-1) less than or similar to nu(eff) less than or similar to 1.5 mu m(-1). This analysis therefore bridges the Gaia team's consistency check of Z(5) for G > 13 and indications from independent analysis using Cepheids of a 15 mu as overcorrection for G < 11. I find overcorrection sets in at G less than or similar to 10.8, such that Z(5)-corrected EDR3 parallaxes are larger than asteroseismic parallaxes by 15 3 mu as. For G greater than or similar to 10.8, EDR3 and asteroseismic parallaxes in the Kepler field agree up to a constant consistent with expected spatial variations in EDR3 parallaxes after a linear, color-dependent adjustment. I also infer an average underestimation of EDR3 parallax uncertainties in the sample of 22% 6%, consistent with the Gaia team's estimates at similar magnitudes and independent analysis using wide binaries. Finally, I extend the Gaia team's parallax spatial covariance model to brighter magnitudes (G < 13) and smaller scales (down to 01), where systematic EDR3 parallax uncertainties are at least 3-4 mu as.

Automated summary

This analysis examines the parallax data in Gaia Early Data Release 3 (EDR3), finding issues with overcorrection at certain brightness levels, and inferring an average underestimation of EDR3 parallax uncertainties at 22% to 6%.