All-Sky Faint DA White Dwarf Spectrophotometric Standards for Astrophysical Observatories: The Complete Sample

TL;DR

This paper expands the set of highly accurate spectrophotometric standards using faint DA white dwarfs across the sky, enabling precise calibration for current and future astronomical observatories from ultraviolet to infrared wavelengths.

Contribution

It introduces 32 new faint DA white dwarf standards with verified flux accuracy, extending the existing CALSPEC system for improved calibration across multiple observatories.

Findings

Achieved flux calibration accuracy better than 0.004 mag rms from 2700 Å to 7750 Å.

Established 35 DA white dwarfs as reliable spectrophotometric standards.

Demonstrated consistency between model and observed fluxes across a broad wavelength range.

Abstract

Hot DA white dwarfs have fully radiative pure hydrogen atmospheres that are the least complicated to model. Pulsationally stable, they are fully characterized by their effective temperature Teff, and surface gravity log g, which can be deduced from their optical spectra and used in model atmospheres to predict their spectral energy distribution (SED). Based on this, three bright DAWDs have defined the spectrophotometric flux scale of the CALSPEC system of HST. In this paper we add 32 new fainter (16.5 < V < 19.5) DAWDs spread over the whole sky and within the dynamic range of large telescopes. Using ground based spectra and panchromatic photometry with HST/WFC3, a new hierarchical analysis process demonstrates consistency between model and observed fluxes above the terrestrial atmosphere to < 0.004 mag rms from 2700 {\AA} to 7750 {\AA} and to 0.008 mag rms at 1.6{\mu}m for the total set of 35 DAWDs. These DAWDs are thus established as spectrophotometric standards with unprecedented accuracy from the near ultraviolet to the near-infrared, suitable for both ground and space based observatories. They are embedded in existing surveys like SDSS, PanSTARRS and GAIA, and will be naturally included in the LSST survey by Rubin Observatory. With additional data and analysis to extend the validity of their SEDs further into the IR, these spectrophotometric standard stars could be used for JWST, as well as for the Roman and Euclid observatories.