THE AC-2000 - THE ASTROGRAPHIC-CATALOG ON THE SYSTEM DEFINED BY THE HIPPARCOS-CATALOG

The AC 2000 is a positional catalog of 4,621,836 stars covering the en tire sky. The average epoch of position is 1907. The data are from the images measured and published as part of the Astrographic Catalogue ( AC). The positions are on the system defined by the Hipparcos Catalogu e, having originally been reduced plate-by-plate using the Astrographi c Catalog Reference Stars. In addition to the astrometric data, magnit udes (on the Tycho B system) and cross-referencing information are inc luded. These positions are valuable for the computation of proper moti ons, and were combined with the positions from the recently released T ycho Catalogue to improve proper motions of almost 1 million stars. Th e resulting catalog is known as the ACT Reference Catalog (the name AC T is from AC 2000 and Tycho). Both the AC 2000 and ACT are now availab le on CD-ROM and can be obtained by contacting the first author above. A World Wide Web site describing various aspects of the reductions is also maintained by the Astrometry Department, US Naval Observatory.