Link between the Optical and Radio Frames from Gaia DR3 Data and VLBI Measurements

TL;DR

This study compares Gaia DR3 optical positions with VLBI radio measurements for 126 radio stars, finding negligible rotation between frames and a small systematic parallax offset, confirming the alignment of optical and radio celestial reference frames.

Contribution

It provides the first detailed analysis of the Gaia DR3 and VLBI frame link using a sizable sample of radio stars, refining the systematic offset and scale factor between the frames.

Findings

No significant rotation detected between Gaia and VLBI frames.

Systematic parallax offset of -0.022 mas identified.

Parallax scale factor close to unity at 1.001.

Abstract

Based on published data, we have assembled a sample of 126 radio stars with the trigonometric parallaxes and proper motions measured by VLBI and available in the Gaia DR3 catalogue (in fact, Gaia EDR3). Our analysis of the Gaia--VLBI proper motion differences for 84 radio stars based on the model of solid-body mutual rotation has revealed no rotation components differing significantly from zero, $(\omega_x,\omega_y,\omega_z)=(0.06,0.08,-0.10)\pm(0.06,0.07,0.08)$ mas yr$^{-1}.$ Based on the trigonometric parallax differences for 90 stars, we have obtained a new estimate of the systematic offset between the optical and radio frames, $\Delta\pi=-0.022\pm0.017$~mas, and showed that the parallax scale factor is close to unity, $b=1.001\pm0.002$.