Spectrophotometric Standards From the Far-UV to the Near-IR on the White Dwarf Flux Scale

The second generation instruments to be installed in 1997 on the Hubble Space Telescope (HST) require spectrophotometric standard stars for flux calibrations to 1.1 μm for the imaging spectrograph (STIS) and to 2.5 μm for the infrared camera (NICMOS). Calculated model atmosphere flux distributions from 0.1 to 3 μm for four pure hydrogen white dwarfs provide the fundamental basis for a new set of spectrophotometric standard stars. Precise visual photometry sets the absolute level of the model fluxes, while FOS spectrophotometry validates the relative V magnitudes to ∼1% and the relative fluxes at other wavelengths to ∼2%. Extensive FOS observations of four more stars from 1140 to 8500 Å expand the set of primary standards to eight stars. These eight flux distributions are compared with IUE fluxes in the UV and with Oke spectrophotometry in the visual to define corrections as a function of wavelength. These corrections plus a wavelength independent correction to the Oke fluxes are accurate to ∼3% and provide 18 additional standards on the WD scale from 1150 to 9200 Å. One more standard a Lyr consists of lUE data plus the ground-based spectrum of Hayes.