Abstract
Jovian satellite Io possesses active volcanic activities and the erupted gas supplys neutrals and ions to the Jovian magnetosphere through the interaction between Io plasma torus and Io. Volcanic gas contains neutral sodium atoms and sodium-bearing molecular ions. They escape from Io through several physical processes which have so far been proposed for ejection of sodium from Io.
In order to understand these ejection processes more clearly, high dispersion spectroscopic observation was carried out at the Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, using a 188-cm telescope and the High Dispersion Echelle Spectrograph (HIDES: R=100,000) on 4 nights in February, 2004 and 3 nights in February, 2005. A number of high dispersion spectra of sodium D1 and D2 emissions were obtained for a region of +/- 1.5RJ (1RJ : Jovian radius = 71492km) centered on Io from the two observations.
In the presentation, ejection velocity distributions of neutral sodium atoms at various Io phase angles will be given. Further, the spatial extent of velocity distribution from Io through the Io's corona to the Jovian magnetosphere will be discussed by comparing observation results with computer simulation results.
