Low Noise Solar and Laboratory Spectroscopy-II: The Region Around 6708 A in the Photospheric Spectrum and the Solar Lithium Abundance

The Oxford low noise spectrometer has been used to record the Fraunhofer spectrum in the region of the lithium resonance lines with a resolving power of 500 000 and an r.m.s. noise level of less than 0.02 per cent of the continuous intensity. As there is no direct evidence of the presence of the lithium lines the spectra can only be used to set an upper limit to the abundance. Computations of possible wavelength shifts in the lines indicate that they should not be shifted from their laboratory wavelengths by more than the errors of the wavelength scale in the spectra. Using this result it is possible to set an upper limit of 0*61 mA to the lithium absorption which corresponds to an abundance $$\text {log} (N_\text {Li}/N_\text H)\leqslant 0.38$$ on the scale of log ( N_H ) = 12.00. This value, although considerably smaller than previously published estimates, is consistent with the observed enhancement of the lines in spot spectra.