Broadband Measurements of Facular Photometric Contrast Using the Solar Bolometric Imager

We present the first photometric measurements of solar faculae in broadband light . Our measurements were made during the recent flight of the Solar Bolometric Imager (SBI), a 30 cm balloon-borne telescope that imaged the Sun with a spectrally constant response between about 0.31 and 2.6 μm. Our curve of facular contrast versus limb distance agrees well with values obtained by the blackbody correction of monochromatic measurements. This decreases uncertainty in the facular irradiance contribution, which limits searches for other possible mechanisms of solar luminosity variation, besides changes of photospheric magnetism.