The celestial reference frame at 24 and 43GHz. I. astrometry

Abstract

We present astrometric results for compact extragalactic objects observed with the Very Long Baseline Array at radio frequencies of 24 and 43GHz. Data were obtained from ten 24 hr observing sessions made over a five-year period. These observations were motivated by the need to extend the International Celestial Reference Frame (ICRF) to higher radio frequencies to enable improved deep space navigation after 2016 and to improve state-of-the-art astrometry. Source coordinates for 268 sources were estimated at 24GHz and for 131 sources at 43GHz. The median formal uncertainties of right ascension and declination at 24GHz are 0.08 and 0.15 mas, respectively. Median formal uncertainties at 43GHz are 0.20 and 0.35 mas, respectively. Weighted root-mean-square differences between the 24 and 43GHz positions and astrometric positions based on simultaneous 2.3 and 8.4GHz Very Long Baseline Interferometry observations, such as the ICRF, are less than about 0.3 mas in both coordinates. With observations over five years we have achieved a precision at 24GHz approaching that of the ICRF but unaccounted systematic errors limit the overall accuracy of the catalogs. © 2010. The American Astronomical Society.