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I. Platais (Yale/USRA), V. Kozhurina-Platais, P. Demarque, T.M. Girard, W.F. van Altena (Yale), A.R. Klemola (UCO/Lick Obs.), WOCS collaboration
The well-known 7-Gyr-old open cluster NGC 188 has been a subject of numerous studies. It is also a cornerstone cluster for the WIYN Open Cluster Study (WOCS) project which aims to produce a comprehensive photometric, astrometric, and spectroscopic database for selected fundamental open clusters. The astrometric aspects of WOCS benefit from deep KPNO and CTIO 4m telescope old material in combination with the NOAO CCD Mosaic Imager frames. The latter presents a certain challenge to obtain astrometric grade positions (see accompanying poster on the CCD Mosaic's geometry).
As an example of WOCS potential we present the first results of BV photometry and new proper motions of NGC 188 down to V=21 mag. We show that there are some cluster members, mostly faint ones, beyond the adopted tidal radius and that the Present Day Mass Function (PDMF) strongly differs from the traditionally accepted shape of the IMF. Hopefully, the WOCS results will trigger more work on N-body simulations from which the IMF can be reconstructed using the observed PDMF.
This study is supported in part by NSF grant AST9819777 to Yale University and NSF grant AST9530632 to UCO/Lick Observatory.