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K.L. Jessup, J. Spencer (Lowell Observatory), G. E. Ballester, R. Yelle (LPL-Arizona University), F. Roessler (University Wisconsin), R. Howell (University Wyoming)
We present the highest spatial resolution UV spectroscopy of Io's atmosphere yet obtained. Observing Io's anti-jovian hemisphere with the 0.1" wide slit of the HST Space Telescope Imaging Spectrograph (STIS), the G230L grating and the NUV-MAMA centered on the Prometheus plume, we covered latitudes from 60 N to 60 S including the volcanos Zamama, Malik, Tupan, and Chaac, as well as SO2 frost plains. We will report the SO and SO2 column densities and SO2 gas temperatures observed in each region. Surprisingly, there is only a modest difference in SO2 column abundance between the Prometheus plume and nearby low-latitude SO2 frost plains.
Additionally, continuum emission is observed over the Prometheus plume and neighboring low latitude regions near 2800 Å. Preliminary analysis indicates that the intensity of these emissions is consistent with that reported by Geissler et al. (1999) for the emissions,assumed to be continuum emission from SO2, observed over the Prometheus plume by Galileo at 4100 Å.
Our model for SO2 gas absorption is based on the most recent SO2 absorption cross-section data. This includes the high resolution (5-7 mA FWHM) Rufus et al. (2001) data taken at 159 K which extends from 1980 to 2200 A, and the 295 K Stark et al. (1999) and Smith et al. (2001) data which has the same resolution as the former and extends from 1980 to 3200 A. The low resolution (0.5 A) 200 K Wu et al. (2000) data which extends from 1980 to 2970 A is also utilized. This model represents the most accurate model of the SO2 gas absorption cross-section possible within the limits of the available SO2 laboratory data.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.