The first USNO CCD Astrograph Catalog

N.Zacharias, S.E.Urban, M.I.Zacharias,
D.M.Hall, G.L.Wycoff, T.J.Rafferty, M.E.Germain, E.R.Holdenried, J.W.Pohlman,
F.S.Gauss, D.G.Monet, L.Winter

US Naval Observatory, Washington DC, USA

Abstract. The USNO CCD Astrograph (UCA) started an astrometric survey in February 1998 at Cerro Tololo, Chile. This first, preliminary catalog (UCAC1) includes data taken up to November 1999 with about 80% of the Southern Hemisphere covered. Observing continues and full sky coverage is expected by mid 2003 after moving the instrument to a Northern Hemisphere site in early 2001. The survey is performed in a single bandpass (579-642 nm), a 2-fold overlap pattern of fields, and with a long and a short exposure on each field. Stars in the magnitude range of 9 to 14 have positional precisions of <= 20 mas. At the limiting magnitude of about R=16 the positional precision is 70 mas. The UCAC aims at a density (stars per square degree) larger than that of the Guide Star Catalog (GSC) with a positional accuracy similar to Tycho. The UCAC program is a major step towards a high precision densification of the optical reference frame in the post-Hipparcos era, and the first stage, the UCAC1 contains over 27 million stars. Preliminary proper motions are included, which were derived from Tycho-2, Hipparcos and ground-based transit circle and photographic surveys for the bright stars (V <= 12.5) and the USNO A2.0 for the fainter stars. The accuracy of the proper motions varies widely, from 1 to over 15 mas/yr. The UCAC1 is available on CD-ROM from the U.S. Naval Observatory.

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