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Title: The Celestial Reference Frame at 24 and 43 GHz. I. Astrometry Authors: Lanyi, G. E.; Boboltz, D. A.; Charlot, P.; Fey, A. L.; Fomalont, E. B.; Geldzahler, B. J.; Gordon, D.; Jacobs, C. S.; Ma, C.; Naudet, C. J.; Romney, J. D.; Sovers, O. J.; Zhang, L. D. Affiliation: AA(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AB(U.S. Naval Observatory, 3450 Massachusetts Ave., NW, Washington, DC 20392-5420, USA ), AC(Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, BP 89, 33271 Floirac Cedex, France ; CNRS, Laboratoire d'Astrophysique de Bordeaux-UMR 5804, BP 89, 33271 Floirac Cedex, France ), AD(U.S. Naval Observatory, 3450 Massachusetts Ave., NW, Washington, DC 20392-5420, USA ), AE(National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA ), AF(National Aeronautics and Space Administration, 300 E. St., SW, Washington, DC 20546, USA ), AG(NVI Inc./NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA ), AH(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AI(NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA ), AJ(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AK(National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801, USA), AL(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AM(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ) Publication: The Astronomical Journal, Volume 139, Issue 5, pp. 1695-1712 (2010). (AJ Homepage) Publication Date: 05/2010 Origin: IOP AJ Keywords: astrometry, catalogs, quasars: general, radio continuum: galaxies, reference systems, techniques: interferometric DOI: 10.1088/0004-6256/139/5/1695 Bibliographic Code: 2010AJ....139.1695L Abstract We present astrometric results for compact extragalactic objects observed with the Very Long Baseline Array at radio frequencies of 24 and 43 GHz. 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 24 GHz and for 131 sources at 43 GHz. The median formal uncertainties of right ascension and declination at 24 GHz are 0.08 and 0.15 mas, respectively. Median formal uncertainties at 43 GHz are 0.20 and 0.35 mas, respectively. Weighted root-mean-square differences between the 24 and 43 GHz positions and astrometric positions based on simultaneous 2.3 and 8.4 GHz 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 24 GHz approaching that of the ICRF but unaccounted systematic errors limit the overall accuracy of the catalogs. Title: The Celestial Reference Frame at 24 and 43 GHz. II. Imaging Authors: Charlot, P.; Boboltz, D. A.; Fey, A. L.; Fomalont, E. B.; Geldzahler, B. J.; Gordon, D.; Jacobs, C. S.; Lanyi, G. E.; Ma, C.; Naudet, C. J.; Romney, J. D.; Sovers, O. J.; Zhang, L. D. Affiliation: AA(Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, BP 89, 33271 Floirac Cedex, France ; CNRS, Laboratoire d'Astrophysique de Bordeaux-UMR 5804, BP 89, 33271 Floirac Cedex, France ), AB(U.S. Naval Observatory, 3450 Massachusetts Ave., NW, Washington, DC 20392-5420, USA ), AC(U.S. Naval Observatory, 3450 Massachusetts Ave., NW, Washington, DC 20392-5420, USA ), AD(National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA ), AE(National Aeronautics and Space Administration, 300 E. St., SW, Washington, DC 20546, USA ), AF(NVI Inc./NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA ), AG(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AH(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AI(NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA ), AJ(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ), AK(National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801, USA ), AL(Remote Sensing Analysis Systems, 2092 Sinaloa Ave., Altadena, CA 91001, USA), AM(Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, USA ) Publication: The Astronomical Journal, Volume 139, Issue 5, pp. 1713-1770 (2010). (AJ Homepage) Publication Date: 05/2010 Origin: IOP AJ Keywords: astrometry, quasars: general, radio continuum: galaxies, surveys DOI: 10.1088/0004-6256/139/5/1713 Bibliographic Code: 2010AJ....139.1713C Abstract We have measured the submilliarcsecond structure of 274 extragalactic sources at 24 and 43 GHz in order to assess their astrometric suitability for use in a high-frequency celestial reference frame (CRF). Ten sessions of observations with the Very Long Baseline Array have been conducted over the course of ~5 years, with a total of 1339 images produced for the 274 sources. There are several quantities that can be used to characterize the impact of intrinsic source structure on astrometric observations including the source flux density, the flux density variability, the source structure index, the source compactness, and the compactness variability. A detailed analysis of these imaging quantities shows that (1) our selection of compact sources from 8.4 GHz catalogs yielded sources with flux densities, averaged over the sessions in which each source was observed, of about 1 Jy at both 24 and 43 GHz, (2) on average the source flux densities at 24 GHz varied by 20%-25% relative to their mean values, with variations in the session-to-session flux density scale being less than 10%, (3) sources were found to be more compact with less intrinsic structure at higher frequencies, and (4) variations of the core radio emission relative to the total flux density of the source are less than 8% on average at 24 GHz. We conclude that the reduction in the effects due to source structure gained by observing at higher frequencies will result in an improved CRF and a pool of high-quality fiducial reference points for use in spacecraft navigation over the next decade.