IBIS

J/ApJ/607/L33       First IBIS Catalog: 20-100keV                  (Bird+, 2004) 
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.