K-band (24 GHz) Celestial Reference Frame
Christopher S. Jacobs  1  
1 : et Propulsion Laboratory - California Institute of Technology

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 August 2023, the K-band data set has
increased to 1187 sources, 153 sessions (48 sessions since 2019 are dual polarization),
and 2.32 million observations (4.8X increase)---as well as adding north-south geometry
from Spain to South Africa and Korea to Australia. This solution from 2023 August 24th
has median formal precisions of 50 μas in α cosδ and 84 μas in δ. The largest spherical
harmonic distortions seen in the K-band CRF vs. ICRF3-SX are a Z-dipole term of 58 +- 6 μas
and a quadrupole 2,0 magnetic term of -48 +- 5 μas and quadrupole 2,0 electric
term of -64 +- 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.

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