Lick Northern Proper Motion program. III. Lick NPM2 catalog

The Lick Northern Proper Motion (NPM) program, a two-epoch (1947-1988) photographic survey of the northern two-thirds of the sky (delta greater than or similar to -23degrees), has measured absolute proper motions, on an inertial system defined by distant galaxies, for 378,360 stars in the magnitude range 8 less than or similar to B less than or similar to 18. The 1993 NPM1 Catalog contains 148,940 stars in 899 fields outside the Milky Way's zone of avoidance. The 2003 NPM2 Catalog contains 232,062 stars in the remaining 347 NPM fields near the plane of the Milky Way. This paper describes the NPM2 star selection, plate measurements, astrometric and photometric data reductions, and catalog compilation. The NPM2 Catalog contains 122,806 faint (B greater than or equal to 14) anonymous stars for astrometry and Galactic studies, 91,648 bright (B < 14) positional reference stars, and 34,868 "special stars" chosen for astrophysical interest. The NPM2 proper motions are on the ICRS system, via Tycho-2 stars, to an accuracy of 0.6 mas yr(-1) in each field. The rms proper-motion precision is 6 mas yr(-1). Positional errors average 80 mas at the mean plate epoch 1968, and 200 mas at the NPM2 catalog epoch 2000. NPM2 photographic photometry errors average 0.18 mag in B and 0.20 mag in B-V. The NPM2 Catalog and the updated (to J2000.0) NPM1 Catalog are available at the CDS Strasbourg data center and on the NPM Web site. The NPM2 Catalog completes the Lick Northern Proper Motion program after a half-century of work by three generations of Lick Observatory astronomers. The NPM Catalogs will serve as a database for research in Galactic structure, stellar kinematics, and astrometry.