Absolute flux calibration of stars: calibration of the reference telescope

Absolute stellar photometry is based on 1970s terrestrial measurements of the star Vega with instruments calibrated using the Planckian radiance from a Cu fixed-point blackbody. Significant advances in absolute radiometry have been made in the last 30 years that offer the potential to improve both terrestrial and space-based absolute stellar photometry. These advances include the development of detector-based radiometry utilizing spectrally tunable laser sources and improved atmospheric transmittance modelling and characterization. We describe the applications of these new technologies for ground-based spectral irradiance measurements of standard stars at wavelengths ranging from 0.35 µm to 1.7 µm.