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The Korean VLBI Network (KVN) is a new mm-VLBI dedicated array withcapability for simultaneous observations at multiple frequencies, up to 129GHz. The innovative multi-channel receivers present significant benefits forastrometric measurements in the frequency domain. The aim of this work is toverify the astrometric performance of the KVN using a comparative study withthe VLBA, a well established instrument. For that purpose, we carried outnearly contemporaneous observations with the KVN and the VLBA, at 14/7 mm, inApril 2013. The KVN observations consisted of simultaneous dual frequencyobservations, while the VLBA used fast frequency switching observations. Weused the Source Frequency Phase Referencing technique for the observational andanalysis strategy. We find that having simultaneous observations results in asuperior performance for compensation of all atmospheric terms in theobservables, in addition to offering other significant benefits for astrometricanalysis. We have compared the KVN astrometry measurements to those from theVLBA. We find that the structure blending effects introduce dominant systematicastrometric shifts and these need to be taken into account. We have testedmultiple analytical routes to characterize the impact of the low resolutioneffects for extended sources in the astrometric measurements. The results fromthe analysis of KVN and full VLBA datasets agree within 2-$\sigma$ of thethermal error estimate. We interpret the discrepancy as arising from thedifferent resolutions. We find that the KVN provides astrometric results withexcellent agreement, within 1-$\sigma$, when compared to a VLBA configurationwhich has a similar resolution. Therefore this comparative study verifies theastrometric performance of KVN using SFPR at 14/7 mm, and validates the KVN asan astrometric instrument.

Verification of the Astrometric Performance of the Korean VLBI Network, using comparative SFPR studies with the VLBA at 14/7 mm