Faint near-ultraviolet/far-ultraviolet standards from swift/uvot, galex, and SDSS photometry

At present, the precision of deep ultraviolet photometry is somewhat limited by the dearth of faint ultraviolet standard stars. In an effort to improve this situation, we present a uniform catalog of 11 newfaint (u ∼ 17) ultraviolet standard stars. High-precision photometry of these stars has been taken from the Sloan Digital Sky Survey and Galaxy Evolution Explorer archives and combined with new data from the Swift Ultraviolet Optical Telescope to provide precise photometric measures extending from the near-infrared to the far-ultraviolet. These stars were chosen because they are known to be hot (20,000 < T_eff < 50,000 K)DAwhite dwarfs with published Sloan spectra that should be photometrically stable. This careful selection allows us to compare the combined photometry and Sloan spectroscopy tomodels of pure hydrogen atmospheres to both constrain the underlying properties of the white dwarfs and test the ability of white dwarf models to predict the photometric measures. We find that the photometry provides good constraints onwhite dwarf temperatures,whichdemonstrates the ability of Swift/UVOT to investigate the properties of hot luminous stars. We further find that the models reproduce the photometric measures in all 11 passbands to within their systematic uncertainties.Within the limits of ourphotometry,we find the standard stars to be photometrically stable. This success indicates that themodels can be used to calibrate additional filters to our standard system, permitting easier comparison of photometry from heterogeneous sources.The largest source of uncertainty in themodel fitting is the uncertainty in the foreground reddening curve, a problem thatis especially acute in the UV.