Abstract
The first results from a new observing programme studying the Io plasma torus and neutral clouds are presented. Images of both Io's sodium cloud and its SII torus were obtained on 11 and 12 Dec 1989 using a focal reducer CCD camera and a tunable Fabry-Perot filter. Masks were used allowing the study of both ansae of the torus simultaneously. The peak brightness in [SII] at 6716Å was 390(±50) Rayleigh at an L-shell of 5.4 (±0.1) R J. The torus was inclined by 7.8(±0.6)° to the Jovian equatorial plane. The line ratio of the forbidden red doublet lines (6716Å/6731Å) was 0.95(±0.15). These results show that the torus conditions in Dec 1989 were significantly different from those at Voyager fly-by but may be similar to conditions observed in Mar 1981 from the ground.
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