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M.H. Stevens (Naval Research Laboratory)
The N2 Carroll-Yoshino (CY) c4\prime1\Sigmau+-X1\Sigmag+ (0,0) and (0,1) Rydberg bands between 95 and 99 nm were observed to be the most prominent N2 emission features in Voyager 1 Ultraviolet Spectrometer (UVS) airglow spectra of Titan. In order to study both the observed bright limb peak and the observed variation of CY(0,v") over the sunlit disk, a radiative transfer model is employed which considers both photoelectron excitation and magnetospheric particle precipitation. The resonant (0,0) band is known to be optically thick so multiple scattering and all known loss processes to the CY(0,v") system are included. Results show that only 23-33% of c4\prime (0) source excitation appears in (0,0)+(0,1), primarily due to the effects of predissociation compounded over multiple scatterings. Such loss rules out photoelectrons as the only source and requires a flux of 1 keV magnetospheric electrons that is between 0.02-0.04 erg/cm2s to fit the disk observations. The relative variation of (0,0)+(0,1) over the sunlit disk can be explained by the variation of solar zenith angle (SZA) specific to each observation. Lower SZAs place photoelectron excitation at lower altitudes where (0,1) optical depths are greater, yielding less emission. The magnitude of the UVS bright limb peak can be accounted for with the same input fluxes, after taking into account the lower incidence angle of precipitating electrons.