An Empirical Determination of the Continuum Source Function in the Solar Photosphere

Limb-darkening observations of the solar photospheric continuum are reanalyzed. A persistent dis- crepancy between theoretical and empirical absorption coefficients is exhibited. It is shown that the dis- crepancy cannot reasonably be attributed to observational errors, errors in the theoretical or experimental cross-sections, or to an anomalous population of the negative hydrogen ion. However, the disparity is removed if a Kothari source function, rather than a Planck source function, applies in the solar photo- sphere. The magnitude and variation of the Kothari parameter are estimated