The Electron Temperature in the Io Plasma Torus Ribbon derived from the Line Ratio between [SIII] emissions

M. Küppers (LASP, Boulder), K. Jockers (MPAe, Katl.-Lindau, Germany)

In the last week of May 1995 the Io plasma torus was imaged in different emissions of [SII], [SIII], and [OIII] using the two-channel focal reducer of the Max-Planck-Institut für Aeronomie attached to 2.2m telescope ot the European Southern Observatory. The presentation concentrates on observations of the [SIII] lines at 6312Å and 9531Å. Our measurement of the intensity ratio between that two lines in the Io torus ribbon corresponds to an electron temperature of 11 tex2html_wrap_inline17 eV, which is substantially higher than values derived from in situ observations by Voyager. We compare that result with Galileo measurements and discuss implications for the interpretation of other data sets and Io torus models.