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D.L. Jones (JPL, Caltech), A.E. Wehrle (ISC, JPL, Caltech), S.C. Unwin, D.L. Meier (JPL, Caltech), B.G. Piner (Whittier College)
The best (most nearly inertial) global reference frame is currently the International Celestial Reference Frame (ICRF) defined by VLBI observations of compact extragalactic radio sources. The positional accuracy of ICRF sources is typically about 0.3 milli-arcseconds. During the next decade the Space Interferometry Mission (SIM) will provide global positions of optical quasars with an expected precision of about 10 micro-arcseconds. There are a number of object in common between the ICRF and SIM source lists, allowing the radio and optical reference frame to be directly connected to high precision. Two important questions are the precision expected for this reference frame tie, and its stability over time. This paper considers the effects of moving the ICRF to higher observing frequencies, the use of narrow-angle differential VLBI in addition to wide-angle VLBI position measurements, and the likely frequency of observations in both the radio and optical, to estimate the expected precision and stability of the radio-optical frame tie in the post-SIM era. Even with the improvements expected in astrometric VLBI measurements, the radio-optical frame tie for the SIM astrometric grid is likely to be limited by errors in the radio positions of ICRF sources.
Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.