Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes

TL;DR

This study confirms a systematic offset of approximately -80 micro-arcseconds in Gaia DR2 parallaxes, indicating Gaia parallaxes are slightly underestimated for certain brightness and distance ranges, with implications for astrometric measurements.

Contribution

The paper provides an independent verification of the Gaia DR2 parallax offset using eclipsing binary data, refining the understanding of Gaia's systematic errors.

Findings

Gaia DR2 parallaxes are systematically underestimated by about 80 micro-arcseconds.

The offset is consistent across distances up to 3 kpc, with slight increase beyond 1 kpc.

The systematic error is below 100 micro-arcseconds, aligning with expectations.

Abstract

We reprise the analysis of Stassun & Torres (2016), comparing the parallaxes of the eclipsing binaries reported in that paper to the parallaxes newly reported in the Gaia second data release (DR2). We find evidence for a systematic offset of $-82 \pm 33$ micro-arcseconds, in the sense of the Gaia parallaxes being too small, for brightnesses $(G \lesssim 12)$ and for distances (0.03--3 kpc) in the ranges spanned by the eclipsing binary sample. The offset does not appear to depend strongly on distance within this range, though there is marginal evidence that the offset increases (becomes slightly more negative) for distances $\gtrsim 1$ kpc, up to the 3 kpc distances probed by the test sample. The offset reported here is consistent with the expectation that global systematics in the Gaia DR2 parallaxes are below 100 micro-arcseconds.