Radio-optical Reference Catalog, Version 1

Abstract

The fundamental celestial reference frame (CRF) is based on two catalogs of astrometric positions: the third realization of the International Celestial Reference Frame (ICRF3), and the much larger Gaia CRF, built from the third data release (DR3). The objects in common between these two catalogs are mostly distant AGNs and quasars that are both sufficiently optically bright for Gaia and radio loud for the VLBI. This limited collection of reference objects is crucially important for the mutual alignment of the two CRFs and the maintenance of all of the other frames and coordinate systems branching from the ICRF. In this paper, we show that the three components of ICRF3 (S/X, K, and X/Ka band catalogs) have significantly different sky-correlated vector fields of position offsets with respect to Gaia DR3. When iteratively expanded in the vector spherical harmonics up to degree 4 on a carefully vetted set of common sources, each of these components includes several statistically significant terms. The median sky-correlated offsets from the Gaia positions are found to be 56 μas for the S/X, 100 μas for the K, and 324 μas for the X/Ka catalogs. The weighted mean vector field is subtracted from the Gaia reference positions, while the deviations from that field are added to each of the ICRF3 components. The corrected positions from each of the four input catalogs are combined into a single weighted mean catalog, which we propose to be the current most accurate realization of an inertial radio-optical CRF.

Time-lapse Very Long Baseline Interferometry Imaging of the Close Active Binary HR 1099

“…High-precision phase-referenced VLBI observations of stars can provide an independent astrometric data set that avoids the biases inherent in quasar position measurements (Lindegren 2020; Chen et al 2023;Makarov et al 2023). Our observations of HR 1099 span a time range of 65 days, which is too short to measure parallax or proper motion precisely.…”

How Well is the International Celestial Reference System Maintained in Official IAU Implementations?

“…Unlike systematic differences between VLBI-based catalogs, there may be additional specific origins of the ICRF minus Gaia-CRF position differences. Different locations of optical and radio centroids can be caused, for example, by AGN jet physics, complicated optical structure of ICRF sources (Petrov & Kovalev 2017a, 2017bPlavin et al 2019), or by possible problems with processing of Gaia observations of extended galaxies (de Souza et al 2014;Makarov et al 2023).…”