SIMBAD references

Context. We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of very long baseline interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources.
Aims. We produce a multifrequency catalog of radio source positions with full variance-covariance information across all radio source positions of all input catalogs.
Methods. We combined three catalogs, one observed at 8GHz (X band), one at 24GHz (K band) and one at 32GHz (Ka band). Rather than only using the radio source positions, we developed a new, rigorous combination approach by carrying over the full covariance information through the process of adding normal equation systems. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined catalog.
Results. The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8GHz, 824 sources also observed at 24GHz, and 674 at 32GHz. The frame is aligned with ICRF3 within ±µas and shows an average positional uncertainty of 0.1mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.