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M. H. Stevens, J. Bishop (NRL), P. D. Feldman (JHU)
Several recent studies have demonstrated the complexity of the relatively bright N2 EUV airglow spectrum both on Earth and on Titan. The emerging details reveal larger contributions to the airglow from features that were not resolvable by the Voyager 1 Ultraviolet Spectrometer (UVS) and smaller contributions from other features that were presumed to be prominent. On September 24-25, 1999, the Far Ultraviolet Spectroscopic Explorer (FUSE) observed the Earth's dayglow between 90.5 and 118.8 nm at a spectral resolution of 0.008 nm, about 400 times better than the UVS. This portion of the EUV spectrum is replete with atomic and molecular emissions excited by photoelectrons and photodissociative ionization of N2. In this work, we model all the important EUV emissions arising from excitation processes involving N2 and compare them to FUSE observations. A critical element of this analysis is the calculation of emission from the readily excited N2 Carroll-Yoshino c4'—X bands, for which the resonant (0,0) band near 95.8 nm is optically thick. Using a multiple scattering model that includes predissociation and branching to more optically thin bands, we calculate the total amount of CY(0,v") emission that is lost or redistributed. Some analyses of UVS data found that CY(0,0)/CY(0,1) ~1.3 at Titan, but the FUSE observations and our model results show that this ratio is ~0.3 on Earth. By calculating the atomic and molecular emissions near 95.8 nm and comparing them to FUSE data, we suggest that other EUV emissions near 95.8 nm are responsible for the feature previously identified as CY(0,0) at Titan.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.