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J. T. Clarke (Univ. of Michigan), J. Ajello (JPL), G. E. Ballester (Univ. of Michigan), L. Ben-Jaffel (IAP - Paris), J. E. P. Connerney (NASA - GSFC), J. -C. G\'erard (Univ. of Liege), G. R. Gladstone (SwRI), W. R. Pryor (Univ. of Colorado), K. Tobiska, J. T. Trauger (JPL), J. H. Waite (SwRI)
HST observations of the UV emissions from Jupiter's aurora have been obtained with the new Space Telescope Imaging Spectrograph (STIS) since July 1997. UV images of the aurora are now possible with an order of magnitude higher sensitivity than possible with earlier cameras, and improved angular resolution from shorter exposures. Images have been obtained at 4 epochs since Sept. 1997, and reveal several new features of the auroral emission pattern. These include i) faint auroral emissions extending roughly 60 deg. in the wake or plasma flow direction beyond Io's magnetic footprint, ii) systematic motions of the main auroral oval both toward the pole and toward the equator at different local times and longitudes, and iii) clear identification of an auroral emission feature with Ganymede's magnetic footprint, from the relative motion of the feature remaining underneath Ganymede in a time series of images. Preliminary interpretations of these features will be presented. Spectra have also been obtained of auroral emission features including the northern and southern main ovals, the diffuse emission poleward of the main oval, and the northern and southern Io footprints. These spectra will be presented with estimates of the overlying hydrocarbon columns, the energy of the exciting electrons, the rotational temperature of the emitting hydrogen, and the overlying column of atomic hydrogen. This work was supported by NASA under grants GO-6743.01-95A and GO-7308.01-96A to the University of Michigan.