Nightglow studies with the world's largest optical telescope

Abstract

Abstract By making use of 0.02-nm-resolution sky spectra from the HIRES echelle spectrograph at the W.M. Keck(I) observatory on Mauna Kea, HI, obtained during normal astronomical observations, we have shown that 650–870 nm emission from the vibrationally-excited levels of the O2(b1Σ+g) state is a significant component of the terrestrial nightglow, with a total average intensity from levels v = 1–15 of approximately 150 R. The b1Σ+g state vibrational distribution is bimodal, with peaks at v = 3, 4 and v = 12, and a deep minimum at v = 8 containing only ∼5% of the v = 3 population. The b-X 0-0 band (the Franhofer A-band) is discernible via isotopic emission, with an intensity comparable to that of the strongest of the new b-X bands. There are indications that the vibrationally-excited b1Σ+g state emissions correlate temporally with the OH Meinel band emission, and satellite measurements appear to show that the relatively strong emission from the O2(b-X) 4-3 band originates at an alitutde near 87 km, i.e. in the OH region. In an 8-minute observation on 20 Nov 1999, the Keck telescope was pointed at Venus, and the first high-resolution nightglow spectrum was recorded in the visible spectral region. The oxygen green line was revealed, with an intensity near 150 R, approximately the same as in the terrestrial atmosphere. The only previous observation, from the Venera 9/10 orbiters, did not detect this emission.