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Session 13 - Surveys, SETI and Pollution.
Display session, Monday, June 08
High-Resolution Study of New Terrestrial Nightglow Features – Beyond OH
T. G. Slanger, P. C. Cosby, and D. L. Huestis, Aeronomy Group, Molecular Physics Laboratory, SRI International, Menlo Park, CA 94025 and D. E. Osterbrock and J. P. Fulbright, University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064
Sky spectra taken with the HIRES echelle spectrometer on the Keck I telescope on Mauna Kea have led to the discovery of an impressive array of new spectral nightglow features, belonging to the O_2(b^1\Sigma_g^+ - X^3/Sigma_g^-) Atmospheric Band system. The previous record for rotationally-resolved spectroscopy in this system has long been held by Babcock and Herzberg (1948), who detected the b^1\Sigma_g^+ state up to v = 3 in solar absorption spectra. Recently, Osterbrock et al. (1996) have published 0.2-Åresolution sky spectra showing levels up to v = 4, and these same data have been further analyzed to reveal that levels up to v = 10 could be seen. With a more recent data set in which signals have been accumulated for up to 120 hours, we are now able to measure levels up to v = 15, which encompasses 3/4 of the b^1\Sigma_g^+ state potential. The discovery of these new spectral features in the O_2 terrestrial nightglow has an impact on our understanding of other planets. The b^1\Sigma_g^+ state, along with the lower-lying a^1\Delta_g state, produces emission which should be discernible in the CO_2 atmospheres of Mars and Venus, as a result of the oxygen-atom recombination which is recognized to be as important a process in those environments as in the terrestrial atmosphere. The a^1\Delta_g state emission, from the v = 0 level, is a well-known though puzzling feature of the Venus atmosphere, both on the day and night sides. From the HIRES observations, and our laboratory program to determine the temperature-dependent effects of atmospheric quenching of vibrationally-excited levels by O_2, N_2, and CO_2, we ultimately expect to be able to predict the intensities to be found on Mars and Venus in these O_2 emission systems.
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