Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared

TL;DR

This paper reviews techniques for absolute flux calibration across ultraviolet to mid-infrared wavelengths, emphasizing the importance of accurate spectral energy distributions for astrophysical measurements and discussing current standards and their precision.

Contribution

It provides a comprehensive review of flux calibration methods, compares stellar SEDs to standards, and discusses recent improvements in calibration accuracy from laboratory and astronomical data.

Findings

Fluxes from visible to near-IR are accurate to about 1%.

Comparison with lab standards shows potential for improved precision.

The CALSPEC standard is based on white dwarf model atmospheres.

Abstract

The measurement of precise absolute fluxes for stellar sources has been pursued with increased vigor since the discovery of the dark energy and the realization that its detailed understanding requires accurate spectral energy distributions (SEDs) of redshifted Ia supernovae in the rest frame. The flux distributions of spectrophotometric standard stars were initially derived from the comparison of stars to laboratory sources of known flux but are now mostly based on calculated model atmospheres. For example, pure hydrogen white dwarf (WD) models provide the basis for the HST CALSPEC archive of flux standards. The basic equations for quantitative spectrophotometry and photometry are explained in detail. Several historical lab based flux calibrations are reviewed; and the SEDs of stars in the major on-line astronomical databases are compared to the CALSPEC reference standard spectrophotometry. There is good evidence that relative fluxes from the visible to the near-IR wavelength of ~2.5 micron are currently accurate to 1% for the primary reference standards; and new comparisons with lab flux standards show promise for improving that precision.