The K-band (24 GHz) Celestial Reference Frame

Abstract: The K-band (24 GHz) Celestial Reference Frame became one of three components of the ICRF-3 in 2018 (Charlot et al, 2020). As of January 2024, the K-band data set has increased to 1315 sources, 161 sessions (55 sessions since 2019 are dual polarization), and 2.57 million observations (4.8X increase)---as well as adding north-south geometry from Spain to South Africa and Korea to Australia. This solution from 2024 January 19th has median formal precisions of 52 μas in α cosδ and 91 μas in δ. The largest spherical harmonic distortions seen in the K-band CRF vs. ICRF3-SX are a Y-rotation term of -46+- 6 μas and quadrupole 2,0 magnetic term of -26 +- 4 μas and quadrupole 2,0 electric term of -35 +- 7 μas. The K-band frame is dominated by the northern geometry of the VLBA. Recently begun observing programs from Yebes, Spain to Hartebeesthoek, South Africa and from the Korean VLBI Network to Mopra, Australia are expected to improve declination precision as well as reduce the above systematic distortions. The prospects for future improvements are bright with the aforementioned north-south baselines as well as plans for increasing VLBA data rates to 8 Gbps, and potentially adding dual band X/K (8/ 24 GHz) to the VLBA with the JPL designed broadband receiver (Kooi et al, 2023) in order to improve ionosphere calibrations.