THE AGK3U - AN UPDATED VERSION OF THE AGK3

We present the details of construction of an updated version of the AGK3. Unlike the builders of the Positions and Proper Motions (PPM) catalog, we have gone forward in time to gain new positions to use to improve the AGK3 proper motions. The source of these new observations is the Palomar "Quick V" survey made for the construction of the Hubble Space Telescope Guide Star Catalog. We have been able to recover individual equatorial coordinates from a Schmidt plate with a typical standard deviation about the mean of 0.33". Moreover, our means (i.e., the systematic errors) are at the 0.01" level. These realistic, external errors compare favorably with the reduction of the AGK3 astrograph material (0.21" per equatorial coordinate). We believe that we have proven that the astrometric potential of large-scale Schmidt plates can be realized via the subplate technique and then successfully integrated with the results of classical photographic astrometry. Our AGK3U positions have a mean error of 0.167" at an average epoch of 1950.62. The new proper motions have a total (i.e., two-dimensional) formal mean error of 0.82"/cy. We present absolute comparisons via the GC. As viewed through the GC, the mean error of an AGK3U star's total proper motion is approximately 1.6"/cy. The AGK3U has been deposited at the National Space Science Data Center and at the Strasbourg Data Center. A second aspect of this work is the extensive "quality assurance" and double-checking we have performed at each stage. The accuracy of the positions from the Schmidt plates, the real soundness of the proper motions, and the assignment of weights for the AGK2, AGK3, and GSC material have all been thoroughly investigated with independent, objective standards.