WIYN Open Cluster Study. XVII. Astrometry and Membership toV=21 in NGC 188

We present techniques for obtaining presision astrometry using oldphotographic plates from assorted large-aperture reflectors in combination withrecent CCD Mosaic Imager frames. At the core of this approach is atransformation of plate/CCD coordinates into a previously constructedastrometric reference frame around the open cluster NGC 188. Our primary resultis a new catalog of proper motions and positions for 7812 objects down to V=21in the 0.75 square degree area around NGC 188. The precision for well-measuredstars is 0.15 mas/yr for proper motions and 2 mas for positions on the systemof the Tycho-2 catalog. The sum of membership probabilities indicates that NGC188 contains 1050 stars down to V=21. Comprehensive lists of the candidate bluestragglers and red giants substantially enlarge the number of such stars knownin NGC 188. We have also obtained a small correction to the proper motions fromthe mean `motion' of background galaxies. (Abridged)Comment: 37 pages, 10 figures. Accepted for publication in The Astronomical Journa