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Paper: Radio-Optical Reference Frame Link: First Results using Dedicated Astrograph Reference Stars
Volume: 338, Astrometry in the Age of the Next Generation of Large Telescopes
Page: 184
Authors: Zacharias, M.I.; Zacharias, N.
Abstract: The radio-optical reference frame link program at USNO (Zacharias & Zacharias 2005) is part of the UCAC (USNO CCD Astrograph Catalog) project. Between 1998 and 2004 deep CCD images around optical counterparts were observed during over 20 runs at Cerro Tololo and Kitt Peak. Contemporaneously with the deep frames, dedicated wide-field CCD images were taken with the astrograph on the same fields. Data from these special observations did not enter the UCAC2 public catalog. For the first time some of these dedicated astrograph observations are reduced to provide a reference star catalog for the June 2001 KPNO 2.1m deep frames. Results from the first 2 nights of that run are presented. The astrograph frames are reduced with Tycho-2 stars to give positions on the Hipparcos system for reference stars to about R=16.5. From 9 to over 150 such reference stars are available for each of the 10 arcmin wide deep fields. The mean standard error of the deep frame reductions is about 25 mas. Positions for 15 optical counterparts are provided. Optical minus radio position differences are on the 10 to 20 mas level for the mean of about 6 deep frames per field.
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