31st Annual Meeting of the DPS, October 1999
Session 58. Io Posters
Poster Group II, Thursday-Friday, October 14, 1999, , Kursaal Center

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[58.06] Eclipse Egress Growth of the Na I Column Density in the Vicinity of Io

C.M. Anderson (Department of Astronomy, University of Wisconsin - Madison), J. Corliss, F. Scherb (U. of Wisconsin - Madison), A.E. Potter (Lunar and Planetary Institute)

We report moderate and high resolution, integral field spectroscopic observations of the neutral Sodium D­lines in the vicinity of Io immediately after Io's egress from the shadow of Jupiter. On 1998 November 8, the McMath Solar Telescope echelle spectrograph with a Bowen image slicer was used to obtain a sequence of 14, five minute exposures after egress. The spectra from each of the ten facets of the image slicer can be subdivided into as many as ten separate spectra yielding a 10 X 10 array of integral field spectra covering a 10 arc second square patch of sky around Io. This instrument delivers a resolution R= 140,000. On 1999 February 1, the WIYN Telescope Multi­Object Spectrograph fed by the "Densepak" fiber optic array obtained a complimentary set of spectra covering a larger area, 30 x 40 arc seconds. These spectra have resolution R = 15,000. Twenty two, 60 second exposures were obtained over a period of 31 minutes post egress. The emission from near Io appears on the steep core of the Solar Fraunhofer line. Io's velocity with respect to the Sun changes significantly over the course of the observations so careful account must be taken of the flux available for fluorescence. When this compensation is done, both data sets show the column density of Sodium increasing with time. The McMath data show that the column density begins to approach a steady state value after about 1.5 hours while the WIYN data shows that the time variable component of the emission is confined to the inner 10 to 15 arc seconds of the Sodium cloud.

This research was supported by NASA grant NAG5­6787

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