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N. Zacharias, T. Corbin, M. Zacharias, T. Rafferty, P.K. Seidelmann, F.S. Gauss (U.S. Naval Observatory)
The U.S. Naval Observatory CCD Astrograph at the Cerro Tololo Interamerican Observatory (CTIO) has been used to derive accurate positions of stars in the 8 to 16 magnitude range in an approximately 1.5 square degree area centered on the Hubble Deep Field South (HDF-S). The positions are on the International Celestial Reference System (ICRS) with a 10 mas accuracy for the zero point. The Hipparcos Catalogue and the ACT Reference Catalog have provided the primary reference stars in a 579 - 642 nm bandpass at mean epoch 1998.6. The accuracy of individual star positions in the 8 to 14 magnitude range is about 20 mas while it is about 50 mas at 16th mag. The 0.9-meter CTIO telescope has been used to extend and densify this net of astrometric reference stars down to about 20th magnitude in the central 12 by 18 arcmin portion of the field. These results have been used to calibrate the data in this field from the CTIO 4-meter Big Throughput Camera (BTC) of the HDF-S. Thus positions of faint stars, also visible with the HST, are on the same coordinate system (ICRS) as defined by extragalactic sources at radio wavelengths. This contribution by the USNO to the HDF-S effort was made possible by the ongoing USNO Astrograph program at CTIO (UCAC-S). This project involves producing accurate positions on the ICRS over the Southern Hemisphere for stars in the 8th to 16th magnitude range. The link to the ICRS is made both through Hipparcos and directly to the optical counterparts of the extragalactic sources via 0.9-meter observations. A description of the project is given on the USNO web site at: http://www.usno.navy.mil/
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The author(s) of this abstract have provided an email address for comments about the abstract: nz@ctioj8.ctio.noao.edu