The Celestial Reference Frame at K Band: The CRF-K-2025 Catalog

Abstract

We present an updated K-band (24 GHz) celestial reference frame (CRF) constructed from ∼3.5 million very long baseline interferometry (VLBI) observations collected during 211 observing epochs between 2002 May and 2025 December using the Very Long Baseline Array, the HARTRAO-HOBART26 baseline, the HARTRAO-YEBES40M baseline, and the Korean VLBI Network augmented with several other VLBI stations. We have successfully observed and determined precise angular coordinates for 1317 compact extragalactic radio sources, essentially quasars, covering the full sky. This updated K-band catalog is designated as CRF-K-2025. The precision of CRF-K-2025 is characterized by median scaled uncertainties of 60 and 104 μas in R.A. and decl., respectively. The increase in number of observations and sensitivity over earlier K-band campaigns has resulted in a catalog with 493 additional sources and a precision approximately 25% better than the ICRF3-K catalog, and similar to the ICRF3-SX catalog. At K band, these quasar radio sources generally show less extended emission than at lower frequencies and thus can potentially provide a more stable long term CRF than at the standard S/X (2.3/8.4 GHz) observing bands of ICRF3-SX.