Spectrophotometric standards from the far-ultraviolet to the near-infrared: STIS and NICMOS fluxes

With photometric repeatability in the 0.2%-0.4% range and wavelength coverage from 1150 to 10,200 Angstrom, the Space Telescope Imaging Spectrograph (STIS) low-dispersion spectrophotometry provides excellent absolute flux standards. STIS observations of 19 stars are used to update the database of Hubble Space Telescope standard stars with absolute fluxes that are based on the white dwarf pure hydrogen scale. Uncertainties in the STIS absolute flux calibration range from 4% in the far-UV to 2% at longer wavelengths. The relative and absolute fluxes of our composite standards in the IR are verified by the Near Infrared Camera and Multi-Object Spectrograph (NICMOS) observations and by ground-based IR photometry.