A new approach to the absolute spectrophotometric calibration of standard stars: Vega and Sirius

Absolute flux calibration of standard stars, traceable to the International System of Units (SI) standards, is essential for 21st century astrophysics. Dark energy investigations that rely on observations of Type Ia supernovae and precise photometric redshifts of weakly lensed galaxies require a minimum uncertainty of 0.5% (k=1) in the absolute color calibration. Other areas of astronomy and astrophysics, e.g. fundamental stellar astrophysics, will also benefit. In the era of large telescopes and all sky surveys, well-calibrated standard stars that do not saturate, are available over the whole sky, and extend to fainter magnitudes are needed. Our collaboration, NIST Stars, has developed a novel, fully SI-traceable laboratory calibration strategy that will enable achieving the demanding 0.5% requirement which we shall describe here. We discuss our results from a pilot study to determine the top-of-the-atmosphere absolute spectral irradiance of bright stars and the next steps.