LOW-RESOLUTION SPECTRA OF THE IO PLASMA TORUS 2 DAYS AFTER THE ULYSSES ENCOUNTER

Low-resolution spectra of the lo plasma torus have been obtained on 10 and 11 February 1992 (2 days after the Ulysses encounter) using the 2 m telescope of the Bulgarian National Observatory. The spectra show t he forbidden line emissions of S+ (lambdalambda 6716, 6731 angstrom) a nd S2+ (lambda 6312 angstrom). Measured intensities are compared with a Voyager-type model. The intensity distribution of [SII] is found to deviate from the model predictions which indicates a change in the tor us at the Ulysses encounter when compared with the Voyager epoch. A co rotating structure was observed, both in [SII] and [SIII], at lambda(I II) = 170-degrees, showing that the torus was not azimuthally symmetri c. The lambda 6716/lambda 6731 and lambda 6731/lambda 6312 line ratios indicate a higher electron density at the time of the Ulysses observa tions. Additionally, the shift of the torus caused by the dawn-dusk el ectric field could be observed. Peak intensities in [SII] were found i t 5.66 +/- 0.02 R(J) on the West ansa and 5.91 +/- 0.04 R(J) on the Ea st.