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Session 16 - Astrometry.
Display session, Wednesday, January 07
Exhibit Hall,

[16.09] Astrometric Calibration Regions with Accurate Star Positions and Magnitudes

R. C. Stone (USNO, Flagstaff Station)

From repeated overlapped CCD scans, positions and magnitudes for 661,591 stars have been established in 16 regions (each approximately 7.6^\circ \times 3.2^\circ) along the celestial equator. There is a wide range in stellar magnitude (9.5 < R < 17.8) and in stellar densities (varying from 770 to 3700 stars deg^2) in these regions. Moreover, the results were determined with precisions of \pm18 mas, respectively in right ascension and declination, and \pm0.011 mag for the stellar magnitudes. The true errors are estimated to be \pm50 mas for the positions and \pm0.018 mag for the magnitudes. These data are currently available and are being improved by increasing the number of observations made of each star and by re-reducing the data using differential reductions and the Tycho reference star catalog. The expected final accuracy of the star positions is \pm10 mas in both coordinates.

These regions are conveniently accessible from both hemispheres and are useful for calibrating the fields of astrographic telescopes and CCD devices (either individually or in mosaiced arrays) in terms of scales, orientations, distortions, positional accuracies, and photometric sensitivities. In particular, these data will be used to established the astrometric properties of the large Sloan Digital Sky Survey (SDSS) CCD survey camera. This paper describes the currently available data, in terms of observations and reductions, and the refined positions and magnitudes which will be available in about a year.

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