TheuBVIPhotometric System. II. Standard Stars

Paper I of this series described the design of a CCD-based photometric systemthat is optimized for ground-based measurements of the size of the Balmerdiscontinuity in stellar spectra. This "uBVI" system combines the Thuan-Gunn ufilter with the standard Johnson-Kron-Cousins BVI filters, and it can be usedto discover luminous yellow supergiants in extragalactic systems andpost-asymptotic-giant-branch stars in globular clusters and galactic halos. Inthe present paper we use uBVI observations obtained on 54 nights with 0.9-mtelescopes at Kitt Peak and Cerro Tololo to construct a catalog of standardizedu magnitudes for standard stars taken from the 1992 catalog of Landolt. Wedescribe the selection of our 14 Landolt fields, and give details of thephotometric reductions, including red-leak and extinction corrections,transformation of all of the observations onto a common magnitude system, andestablishment of the photometric zero point. We present a catalog of umagnitudes of 103 stars suitable for use as standards. We show that dataobtained with other telescopes can be transformed to our standard system withbetter than 1% accuracy.Comment: 24 pages, 4 figures, 4 tables; accepted by A