Gaia EDR3 Parallax Zero-point Offset based on W Ursae Majoris-type Eclipsing Binaries

TL;DR

This study independently measures Gaia EDR3 parallax zero-point offsets using W UMa-type eclipsing binaries, confirming the effectiveness of Gaia's correction and mapping spatial variations with high precision.

Contribution

It introduces a new method using W UMa-type binaries to accurately determine Gaia parallax zero-point offsets and assesses their spatial distribution across the sky.

Findings

Global parallax offset before correction: -28.6 to -25.4 μas.

Post-correction offset: approximately 4.2 to 4.6 μas.

Bias is less than 10 μas over 40% of the sky.

Abstract

We independently determine the zero-point offset of the Gaia early Data Release-3 (EDR3) parallaxes based on $\sim 110,000$ W Ursae Majoris (EW)-type eclipsing binary systems. EWs cover almost the entire sky and are characterized by a relatively complete coverage in magnitude and color. They are an excellent proxy for Galactic main-sequence stars. We derive a $W1$-band Period-Luminosity relation with a distance accuracy of $7.4\%$, which we use to anchor the Gaia parallax zero-point. The final, global parallax offsets are $-28.6\pm0.6$ $\mu$as and $-25.4\pm4.0$ $\mu$as (before correction) and $4.2\pm0.5$ $\mu$as and $4.6\pm3.7$ $\mu$as (after correction) for the five- and six-parameter solutions, respectively. The total systematic uncertainty is $1.8$ $\mu$as. The spatial distribution of the parallax offsets shows that the bias in the corrected Gaia EDR3 parallaxes is less than 10 $\mu$as across $40\%$ of the sky. Only $15\%$ of the sky is characterized by a parallax offset greater than 30 $\mu$as. Thus, we have provided independent evidence that the parallax zero-point correction provided by the Gaia team significantly reduces the prevailing bias. Combined with literature data, we find that the overall Gaia EDR3 parallax offsets for Galactic stars are $[-20, -30]$ $\mu$as and 4-10 $\mu$as, respectively, before and after correction. For specific regions, an additional deviation of about 10 $\mu$as is found.