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I. Platais (Johns Hopkins University), V. Kozhurina-Platais (Space Telescope Science Institute), R.D. Mathieu (University of Wisconsin - Madison), P. Demarque, T.M. Girard, W.F. van Altena (Yale University)
The old open cluster NGC 188 is a cornerstone cluster for the WIYN Open Cluster Study (WOCS). In 2000 we presented first results of deep BV photometry and proper motions of NGC 188. In the meantime, the astrometric properties of the NOAO CCD Mosaic Imager have become better understood. Also, to the existing measurements of KPNO 4-m telescope plates we have added Mt. Wilson 60-in and Palomar 5-m telescope plates taken in the nineteen fifties. As a result, the precision of proper motions has improved by a factor of three, reaching 0.15 mas/yr for the best measured stars. These high-quality proper motions allow us to separate field stars from the cluster members with confidence. Some 1,100 bona fide cluster members are found over the one-degree area down to V=21. We discuss essential properties of NGC 188 in light of the new astrometry, photometry and radial velocities.
This study is supported by NSF grant AST-0196075 to The Johns Hopkins University and NSF grant AST-9731302 to the University of Wisconsin - Madison
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.