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N. Zacharias, S.E. Urban, T.J. Rafferty (USNO), L. Winter (Hamburg Observatory)
Between 1928 and 1931 the sky north of declination -5 degrees was photographed on 1940 glass plates (each covering over 5 by 5 degrees) with two dedicated astrographs (scale 100''/mm) located in Bonn and Hamburg, Germany. The resulting catalog, called ``Zweiter Katalog der Astronomischen Gesellschaft'', AGK2, contains about 186,000 stars. However, \approx 10 times more stars are measurable on the plates.
In 2001 Hamburg Observatory loaned all AGK2 plates to the U.S. Naval Observatory (USNO) for remeasurement. The USNO StarScan machine in Washington DC started to measure those plates in early 2002; measuring should finish mid 2003. All images on all plates are digitized with a CCD camera behind a telecentric lens. The repeatability of the StarScan machine is \approx 0.2 micron and measurements are believed to be accurate to 0.5 micron. Images down to \approx B=12 are measured from these fine-grain emulsions.
Hipparcos stars are used for reference and preliminary positions have been obtained for over 950,000 stars from a sub-set of the plates (+20\circ to +55\circ declination). For well-exposed images, positional errors on the order of 70 mas per star coordinate are obtained. These data were used as part of the proper motion program of the second USNO CCD Astrograph Catalog release (UCAC2). Based on the AGK2 and UCAC2 positions, proper motions of 1 mas/yr are obtained, which is a factor of \approx 2 better than previously best known (from AC2000-Tycho2) for stars in this magnitude range. The final AGK2 data will have significant implications for galactic kinematics and other areas of research.
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The author(s) of this abstract have provided an email address for comments about the abstract: nz@usno.navy.mil
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.