The Palomar-Green catalog of ultraviolet-excess stellar objects

The Palomar-Green Catalog of Ultraviolet Excess Stellar Objects is presented, with data consisting of positions on the sky accurate to about 8 arcsec in each coordinate, photographic B-magnitudes accurate to 0.29 mag, spectral types, some cross references, and photoelectric broadband, multichannel, and Stromgren colors when available. Extensive discussion is given on magnitude calibration using a combination of photoelectric measurements and star count modeling, and on the statistical completeness of the sample based on internal and external tests. Of the 1874 objects in the catalog, 1715 comprise a statistically complete sample covering 10,714 square degrees from 266 fields taken on the Palomar 18-inch (46-cm) Schmidt telescope. Limiting magnitudes vary from field to field, distributed around B = 16.1 mag, ranging from 15.49 to 16.67. The dominant population is that of the hot, hydrogen atmosphere subdwarfs, the sdB stars, which comprise nearly 40 percent of the sample. At 16th magnitude, the hot subdwarf (sdB, sdO) number counts are increasing by about a factor of 2 per mag, the hot white dwarfs by 4 per mag, and quasars by 8 per mag. The result is a very different mix of spectral types expected at 18th mag than is found at 16th mag. The suggestion is made that the sdB stars are part of the old disk rather than a halo population.