Observations of Solar Limb Darkening Between 0.5 and 10.2μ

Abstract

Measurements of solar limb darkening are tabulated for thirteen wave lengths between 0.5 and 10.2 . Observations in the wave-length region 0.5-2.2 were carried out with the McGregor Tower telescope and spectrometer for the interval cos 0 = 1.0 to cos 0 = 0.16. Measurements at three longer wave lengths were made with a Perkin-Elmer spectrometer attached to the 24inch reflector and covered the interval cos 0 = 1.0 to cos 0 = 0.2. At certain wave lengths the near infrared measurements agree with those of Abbot's to within 0.1 per cent; at other wave lengths the systematic differences are as large as 1 per cent. It is found that the degree of limb darkening decreases in the infrared from 3.5 to 10.2 . This result is qualitatively consistent with a systematic increase of the solar continuous opacity toward longer wave lengths in the infrared, as predicted by theoretical calculations of the absorption coefficient of the negative hydrogen ion.