The infrared colors of the Sun

Abstract

Solar infrared colors provide powerful constraints on the stellar effective temperature scale, but they must be measured with both accuracy and precision in order to do so. We fulfill this requirement by using line-depth ratios to derive in a model-independent way the infrared colors of the Sun, and we use the latter to test the zero point of the Casagrande et al. effective temperature scale, confirming its accuracy. Solar colors in the widely used Two Micron All Sky Survey (2MASS) JHKs and WISE W1-4 systems are provided: (V - J) = 1.198, (V - H) = 1.484, (V - Ks ) = 1.560, (J - H) = 0.286, (J - Ks ) = 0.362, (H - Ks ) = 0.076, (V - W1) = 1.608, (V - W2) = 1.563, (V - W3) = 1.552, and (V - W4) = 1.604. A cross-check of the effective temperatures derived implementing 2MASS or WISE magnitudes in the infrared flux method confirms that the absolute calibration of the two systems agrees within the errors, possibly suggesting a 1% offset between the two, thus validating extant near- and mid-infrared absolute calibrations. While 2MASS magnitudes are usually well suited to derive , we find that a number of bright, solar-like stars exhibit anomalous WISE colors. In most cases, this effect is spurious and can be attributed to lower-quality measurements, although for a couple of objects (3% ± 2% of the total sample) it might be real, and may hint at the presence of warm/hot debris disks.