Homogeneous Photometry for Star Clusters and Resolved Galaxies. II. Photometric Standard Stars

摘要

Stars appearing in CCD images obtained over 224 nights during the course of69 observing runs have been calibrated to the Johnson/Kron-Cousins BVRIphotometric system defined by the equatorial standards of Landolt (1992, AJ,104, 340). More than 15,000 stars suitable for use as photometric standardshave been identified, where "suitable" means that the star has been observedfive or more times during photometric conditions and has a standard error ofthe mean magnitude less than 0.02 mag in at least two of the four bandpasses,and shows no significant evidence of intrinsic variability. Many of these starsare in the same fields as Landolt's equatorial standards or Graham's (1982,PASP, 94, 244) southern E-region standards, but are considerably fainter. Thisenhances the value of those fields for the calibration of photometry obtainedwith large telescopes. Other standards have been defined in fields containingpopular objects of astrophysical interest, such as star clusters and famousgalaxies, extending Landolt-system calibrators to declinations far from theequator and to stars of sub-Solar chemical abundances. I intend to continue toimprove and enlarge this set of photometric standard stars as more observingruns are reduced. The full current database of photometric indices is beingmade freely available via a site on the World-Wide Web, or by direct request tothe author. Although the contents of the database will evolve in detail, at anygiven time it should represent the largest sample of precise BVRI broad-bandphotometric standards available anywhere.