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E. Lellouch (Observatoire de Paris, France), G. Paubert (IRAM Granada, Spain), D.F. Strobel (JHU, Baltimore), M. Belton (NOAO, Tucson)
New millimeter-wave observations of Io were obtained on October 9-11 and November 25-27, 1999, using the 30-m IRAM radiotelescope at Pico Veleta, Spain, as part as the Earth-based campaign in support of the Galileo Io observations. Observations, similar in technique to our previous observations in 1990--1995 (e.g. Lellouch et al. Icarus, 98, 271, 1992), were mostly targeted at SO2 lines. SO was also reobserved, and attempts to detect other species (H2S, OCS, NaOH, S2O, CS, ClO) were unsuccessful.
Compared to our previous observations, the SO2 lines appeared somewhat stronger. Combined with very good sky conditions and improved instrumental performances, this allowed us to easily detect several SO2 weak lines (e.g. at 146.605 and 104.239 GHz) that we had desperately looked for in the past. In addition, the high signal-to-noise obtained on the SO2 strong lines (e.g. 221.965 GHz) allows us to monitor line characteristics as a function of orbital position, with a typical time resolution of about 1 hour.
Observational results will be presented, and the data will be interpreted in the context of static and volcanic atmospheres and in the light of recent HST and Galileo observations.