WCSTools Publications presented at the Thirteenth Annual Conference on Astronomical Data Analysis Software and Systems (ADASS 98) in Strasbourg, France in October 2003, to be published in Astronomical Data Analysis Software and Systems XIII, A.S.P. Conference Series, 2004

A Comparison of Large All-Sky Catalogs

by Douglas J. Mink, Warren R. Brown, and Michael J. Kurtz
Harvard-Smithsonian Center for Astrophysics

To compare observations of objects made at various wavelengths, such as are to be found in the Virtual Observatory, good positions are needed. New instruments for ground-based observing, such as multi-fiber spectrographs, also need very accurate positions for objects fainter than those already catalogued. Recent large catalogs, such as the US Naval Observatory's 526,280,881 source A2.0 and 1,036,366,767 source B1.0 Catalogs, the 998,402,801 source Guide Star Catalog II, the 470,992,970 source 2 Micron All Sky Survey Point Source Catalog, and the 48,366,996 soruce USNO CCD Astrometric Catalog have revolutionized our ability to do astrometry with CCD images. The recently published FITS World Coordinate System standard has provided a standard way of parameterizing that astrometry, and the WCSTools and SExtractor software packages allow the automation of the "plate-fitting" process. As part of a survey to be conducted with one of these new spectrographs, we have amassed 1728 15 by 30 arcminute CCD images of a portion of the northern sky. After matching 200 to 400 point sources per image to the various catalogs and fitting world coordinate systems to them using the IMWCS program, we find mean residuals between observed and catalog star positions of between 0.09 and 0.25 arcseconds for the latest catalogs.

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