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C. Emerich (IAS-Orsay & IAP-Paris), L. Ben Jaffel (IAP-Paris), J.T. Clarke, Y. Kim (Michigan University), G.E. Ballester (LPL-Arizona University), R. Prangé (IAS-Orsay), J. Sommeria (ENS-Lyon)
H Ly-\alpha observations of the Jovian disc were made near the 1999 opposition by the STIS instrument during Cycle-8 of HST. Despite the failure of the HST Target Acquisition System just during the course of our measurements program, a new method of analyzing the H Ly-\alpha emission profiles was tried to study the corresponding emission processes.
The large slit entrance of 52 \arcsec \times 0.5 \arcsec that was used for the observations, permitted to make simultaneous measurements of the Jupiter and sky background spectra, providing an accurate correction of this background. On the other hand, combining the long aperture with the capabilities of the STIS spectro-imager, a detailed spectral analysis of the Jovian Ly-\alpha emission was performed. The flux variation from the limb to the interior of the planet is analyzed in 20 spectral ranges (~2 pm wide) and compared with radiative transfer model calculations.
This method seems promising to better understand the physical processes as well as the kind of redistribution function at work in Jupiter's upper atmosphere. Preliminary results comparing the bulge and the anti-bulge regions are presented and discussed.