1999AJ....117.2552W

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.