P21A-3904:
Ground-Based Observations of the Io Plasma Torus in Support of the EXCEED Mission
Tuesday, 16 December 2014
Andrew J Steffl, Southwest Research Institute, Boulder, CO, United States, Masato Kagitani, Tohoku University, Sendai, Japan, Constantine Tsang, Southwest Research Institute Boulder, Boulder, CO, United States and Sarah Victoria Badman, University of Lancaster, Lancaster, LA1, United Kingdom
Abstract:
We acquired spectra of the Io plasma torus in the 5330-7670Å range on January 3-9, 2014 using the RC spectrograph on the Mayall 4m Telescope at Kitt Peak National Observatory. Our data contain emission lines from the two dominant ionization states of sulfur and oxygen (S2+and O+) as well as S+ and Na. From these, we derive the local electron density and the ratio of O+ to S2+ and S+ in the torus. Since these quantities are difficult or impossible for the JAXA EXCEED mission to measure directly, our data are quite complementary. In contrast to the FUV, the brightness of the optical wavelength emissions peaks in the "ribbon" region of the torus, a consequence of the factor of 5 lower photon energies. S+ also shows a secondary brightness peak in the cold inner torus region. Typical observed electron densities in the ribbon region are around 3000 cm-3.
