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A.I.F. Stewart, L.W. Esposito, W.R. Pryor (LASP, Univ. of Colorado at Boulder), J.L. Fox (Physics Dept, Wright State Univ., Dayton, Ohio), UVIS Team
Cassini UVIS measurements of Venus's dayside airglow included the CO Fourth Positive bands, as well as atomic and ionic emissions from H, O, C, N, He, O+, C+, and C++. We have constructed models of the Fourth Positive emissions using the VTS3 model of the neutral thermosphere, and incorporating dissociative excitation (of CO2), direct excitation (of CO), dissociative recombination (of CO2+), and fluorescence by solar FUV as production mechanisms. Each mechanism produces its own characteristic distribution of vibrational levels in the upper state, and in addition the dissociative mechanisms produce excited CO with higher rotational temperatures than the mechanisms acting directly on CO. Solar Lyman-alpha, which pumps the v' = 14 level, penetrates much deeper into the thermosphere than do the other excitation sources and so members of this sequence are sensitive to CO densities at these lower altitudes. We will present the preliminary results of our investigation into the relative importance of the various excitation mechanisms, and into the distribution of CO in the morning equatorial thermosphere. This work was supported by NASA's Cassini project at JPL.