Systematics and accuracy of VLBI astrometry: A comparison with Gaia Data Release 2
Global systematics of ICRF3 against Gaia DR2 (Liu et al. 2020, A&A 634, A28)Abstract
We investigate the overall properties of the ICRF3 using Gaia DR2 as an external reference. Comparing VLBI positions at S/X, K, and X/Ka with optical counterparts (G < 18.7), we analyze formal errors, declination dependence, and global systematics via vector spherical harmonics. The ICRF3 S/X-frame shows improved accuracy and near–zonal-error-free behavior, consistent with Gaia-CRF2. K and X/Ka frames achieve high formal precision but exhibit zonal systematics, including a significant glide along the Z-axis (>200 μas) in X/Ka, likely due to sparse observations and southern geometry.
We compare the ICRF catalogs (ICRF1/2/3) with Gaia DR2 using vector spherical harmonics (VSH) to characterize
global differences (rotation, glide, quadrupoles).
The ICRF3 S/X catalog agrees with Gaia DR2 at the ~30 μas level globally and is nearly free of declination-dependent
(zonal) errors, reflecting improvements from southern re-observations, VCS-II updates, and modeling of Galactic aberration.
The K and X/Ka frames reach better formal precision but show noticeable zonal terms; X/Ka exhibits a
200 μas glide along Z and >100 μas quadrupole components, attributed to sparse sources and weak southern geometry. These results emphasize the need for denser southern coverage at high frequencies to reduce zonal systematics.
Citation:
Liu, N., Lambert, S. B., Zhu, Z., & Liu, J.-C. (2020). Systematics and accuracy of VLBI astrometry: A comparison with Gaia Data Release 2.
Astronomy & Astrophysics, 634, A28.
https://doi.org/10.1051/0004-6361/201936996
Niu Liu
Assistant Professor
My research focuses on astronomical reference systems, VLBI astrometry, space astrometry, and pulsar astrometry.
Zi Zhu
Professor
My research focuses on astrometric methods, astronomical reference systems, and Galactic astronomy.
Jia-Cheng Liu
Professor
My research interests include theoretical mechanics, space astrometry, and astronomical reference systems.