Photometry and Spectroscopy of Faint Candidate Spectrophotometric Standard da White Dwarfs

We present precise photometry and spectroscopy for 23 candidate spectrophotometric standard white dwarfs. The selected stars are distributed in the Northern hemisphere and around the celestial equator, and are all fainter than r ∼ 16.5 mag. This network of stars, when established as standards and together with the three Hubble Space Telescope primary CALSPEC white dwarfs, will provide a set of spectrophotometric standards to directly calibrate data products to better than 1%. In future deep photometric surveys and facilities, these new faint standard white dwarfs will have enough signal-to-noise ratio to be measured accurately while still avoiding saturation. They will also fall within the dynamic range of large telescopes and their instruments for the foreseeable future. This paper discusses the provenance of the observational data for our candidate standard stars. A comparison with models, reconciliation with reddening, and the consequent derivation of the full spectral energy density distributions for each of them is reserved for a subsequent paper.