Investigations of potassium, lithium, and sodium emission in the nightglow and OH cross calibration

Abstract

Sky spectra from the high‐resolution echelle spectrometer (HIRES) on the Keck I telescope have been analyzed to obtain information on the potassium, lithium, and sodium resonance line emission in the nightglow. Relative intensity calibration is carried out against OH band intensities, and absolute values are obtained by utilizing new averaged intensities of the OH 9–4 band. The D1 line of potassium, at 7699 Å, is shown to be present, as previously speculated by Swider [1987]. Its average intensity is 1.0 R, twice as large as predicted. Any lithium line emission at the resonance wavelengths near 6708 Å is obscured by the PP(3) line of the 12‐9 emission band of the O2 (b1Σg+−X3Σg−) Atmospheric Band system. However, as that line has an intensity of ∼60 mR, our estimated upper limit on the Li line intensities is ∼15 mR. The intensity that we extract for the Na(D1) line, averaged over 4 years, is 20 R. Although there is no solar scattering contribution to the Na and K data, the Na D2/D1 line intensity ratio is substantially smaller than reported earlier for nightglow conditions. Observing that the Na/K D1 line intensity ratio is an order of magnitude smaller than the typical [Na]/[K] concentration ratio leads to the conclusion that the maximum efficiency for production of mesospheric Na(2P) is 0.1.