Astrometric calibration regions along the celestial equator

This paper presents accurate J2000 equatorial coordinates and magnitudes for 661 591 stars observed in 16 astrometric calibration regions located around the celestial equator. The size of each region is about 7.60 degrees x 3.2 degrees and includes large numbers of stars (18 799 to 91 058 stars) at high stellar densities (770 to 3720 stars deg(-2)) and with magnitudes 9.5<R<17.8 mag. The positions and magnitudes were determined from overlapped CCD strip scans made in 1994-1996 and are internally accurate to +/-18 mas, respectively, in right ascension and declination, and +/-0.011 mag in magnitude for the brighter stars (R<15 mag), and these errors are about 3 times larger for the faintest stars. The true errors in these positions and magnitudes are probably +/-41 and +/-50 mas in right ascension and declination and +/-0.018 mag for the magnitudes. Each star was observed 8-11 times in the observing program, and all the positions were determined directly in the extragalactic reference frame. A full description of the reduction methods is given as well as particulars about the resulting catalog of star positions and magnitudes. Because these regions are large in size, contain high densities of stars with accurate positions and magnitudes, and are accessible from both hemispheres, they are useful for many practical purposes which are discussed in Sec. 7 of this paper. (C) 1997 American Astronomical Society. [S0004-6256(97)01912-2].