Towards a Network of Faint DA White Dwarfs as High-Precision Spectrophotometric Standards

We present initial results from a program aimed at establishing a network of hot DA white dwarfs to serve as spectrophotometric standards for present and future wide-field surveys. These stars span the equatorial zone and are faint enough to be conveniently observed throughout the year with large-aperture telescopes. Spectra of these white dwarfs are analyzed to generate a non-local-thermodynamic-equilibrium (NLTE) model atmosphere normalized to HST colors, including adjustments for wavelength-dependent interstellar extinction. Once established, this standard star network will serve ground-based observatories in both hemispheres as well as space-based instrumentation from the UV to the near IR. We demonstrate the effectiveness of this concept and show how two different approaches to the problem using somewhat different assumptions produce equivalent results. We discuss lessons learned and the resulting corrective actions applied to our program.
Comment: (15 pages, 7 figures, 5 tables, accepted for publication in ApJ)