The Solar Disk Spectrum Near 6708 Å

The spectrum of the solar disk in the region of the lithium resonance lines (6708 A) has been measured with a resolution of 3 X 10 and high photometric precision (about 0.014 per cent of the continuum), using the solar image formed by the McMath solar telescope at Kitt Peak National Observatory and the spectrometer, a pressure-scanned instrument whose dispersive elements consist of an interference filter and three Fabry-Perot interferometers The profile of the very weak lines observed (having central depths of about 1 per cent of the continuum) is difficult to explain on the basis of lithium absorption. A computer program has been used to decompose the observed absorption into a sum of Gaussians, with the result that the observed spectrum in the region of the lithium lines can be fitted very easily by two non-lithium lines, but only with great difficulty with the lithium profile. The conclusion is that there is no evidence for the existence of lithium in the solar atmosphere from the Fraunhofer spectrum of the disk.