Quasars to B greater than 22.5 in selected area 57 - A catalog of multicolor photometry, variability, and astrometry

The authors present a catalog of 77 quasar candidates at the north galactic pole (Selected Area 57) to a blue magnitude limit of 22.5 over an area of 0.3 square degree. The catalog is based on data from 15 deep 4-m plates and includes photographic UBVI photometry, an index of variability, and proper motions for all but two of the objects. Spectroscopy of over half the sample yields 27 redshifts for galaxies and quasars. Candidates are selected photometrically. The lack of large numbers of nonultraviolet-excess candidates at faint magnitudes suggests that very faint quasars with redshifts greater than 2.5 are rare. The counts similarly limit the existence of a large population of primeval galaxies that otherwise resemble quasars in color and image size. The authors demonstrate that variability and proper-motion data are potentially powerful and complementary techniques to separate true quasars from peculiar subdwarfs and white dwarfs.