The infrared colors of the Sun

Abstract: Solar infrared colors provide powerful constraints on the stellar effective temperature scale, but to this purpose they must be measured with both accuracy and precision. We achieve this requirement by using line-depth ratios to derive in a model independent way the infrared colors of the Sun, and use the latter to test the zero-point of the Casagrande et al. (2010) effective temperature scale, confirming its accuracy. Solar colors in the widely used 2MASS -J H K- and WISE -W1 W2 W3 W4- systems are provided. 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 agree 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 effective temperatures, we find that a number of bright, solar-like stars exhibit anomalous WISE colors. In most cases this effect is spurious and traceable to lower quality measurements, although for a couple of objects (3 +/- 2 % of the total sample) it might be real and hints towards the presence of warm/hot debris disks.