Infrared spectra of two celestial objects frequently used as flux standards are calibrated against an absolute laboratory flux standard at a spectral resolving power of 100 to 200. The spectrum of the K1.5 III star α Boo is measured from 3 to 30 μm, and that of the C-type asteroid 1 Ceres from 5 to 30 μm. While these "standard" spectra do not have the apparent precision of those based on calculated models, they do not require the assumptions involved in theoretical models of stars and asteroids. Specifically, they provide a model-independent means of calibrating celestial flux in the spectral range from 12 to 30 μm, where accurate absolute photometry is not available. The agreement found between the spectral shapes of α Boo and Ceres based on laboratory standards and those based on observed ratios to α CMa (Sirius) and α Lyr (Vega), flux-calibrated by theoretical modeling of these hot stars, strengthens our confidence in the applicability of the stellar models as primary irradiance standards.
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