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J. R. Spencer, K. L. Jessup (Lowell Obs.), E. Lellouch (Obs. Paris, Meudon), M. Richter, T. Greathouse (Univ. Texas, Austin), M. Lopez-Valverde (Inst. Astrofis. Anadalucia), J-M. Flaud (Univ. Paris-Sud)
We report the first ground-based IR observations of Io's atmosphere. We observed 15 lines of the \nu2 band of gaseous SO2 in the 18.9 \mum (529 cm-1) region, at a resolution of 50,000, with the TEXES mid-infrared spectrograph on the IRTF in November 2001. The lines appeared in absorption, probably due to non-LTE effects that produce absorption even for atmospheric kinetic temperatures comparable to surface temperatures. Line strength varied strongly with orbital longitude, being greatest on the anti-Jupiter hemisphere. We also attempted a detection of the SO2 \nu3 band at 7.4 \mum, seen by Voyager over Loki in 1979. A 15-minute integration showed no absorption at sensitivity levels that should easily have detected the absorption strength seen by Voyager at Loki, indicating that this spectral region also holds promise for ground-based studies. Modeling is under way and initial results will be presented.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.