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G.E. Ballester, F. Herbert, A.L. Broadfoot, B.R. Sandel (LPL, U. Arizona)
We present results from UV observations of the Io plasma torus performed by UVSTAR (Ultraviolet Spectrograph Telescope for Astronomical Research) on the STS-95 shuttle flight. UVSTAR consists of two 12 inch telescopes, each with a long-slit spectrograph at the prime focus and a detector consisting of a microchannel plate feeding into a CCD. The spectrographs cover the EUV 500--950{\thinspace Å} and FUV 800--1300{\thinspace Å} spectral regions. Over the period of 1-6 November 1998, five ~15-minute observations were made simultaneously in both channels, and 5 additional observations were made in the FUV. Spectrally-resolved images of the torus were obtained showing several emission features from singly- and doubly-ionized sulfur and oxygen collisionally excited by the torus electrons. Cross-calibration is achieved by comparison of the SII{\,\lambda908} multiplet which is present in both the EUV and FUV spectra.
Emissions from the east and west ansae are separated within a given exposure, yielding data at a total of 10 longitudinal regions. A one-dimensional emission spectrum is deconvolved from each dataset, using the SIII{\,\lambda685} feature as an approximation of a monochromatic torus image. Information on the torus electron temperature, total plasma density, and relative ion abundances will be derived for each ansa by model fitting, as a function of System III longitude, Io phase and time.
Support for this work has been provided by NASA grants NAG5-4158, NAG5-6362 and NAG5-8051 to the University of Arizona.
The author(s) of this abstract have provided an email address for comments about the abstract: gilda@vega.lpl.arizona.edu