STUDY ON IONIZATION PROCESS OF VOLCANIC GAS ORIGINATED FROM JOVIAN SATELLITE IO BASSED ON OPTICAL OBSERVATION AT HALEAKALA

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Optical observations in this research were carried out at Haleakal High Altitude Observatory annually in February and March every year when Jupiter was close to its opposition.Observation of sulfur ion emission in the Io plasma torus was preliminary tried using a combination of 28cm Schmidt-Cassegrain telescope and a cooled CCD camera equipped with an interference filter in fiscal year of 2002. In fiscal year of 2003, observation was carried out using a newly developed Fabry-Perot imager with wavelength resolving power of 60,000, which was connected to a 35cm Schmidt-Cassegrain telescope. Same observation was continued also in fiscal year of 2004. By using a Fabry-Perot imager, it became possible to make Doppler resolved observation. This allowed us to obtain 2-dimensional distributions of intensity of sulfur ion emission, bulk velocity of sulfur ions in the plasma torus and its deviation from corotation of Jovian magnetic field, and ion temperatures both parallel and perpendicular to the magnetic field line.As for sodium emission, observations of sodium nebula extending by 400 Jovian radii from Jupiter were carried out using a wide field imaging instrument with a field of view of 5.7 degree in each year. In addition to these observations, in fiscal year of 2004, observation of distribution of sodium emission in close proximity of lo was made using a Fabry-Perot imager coupled to a 3.7m AEOS telescope equipped with an adaptive optics system. This observation allowed us to obtain asymmetric distribution of sodium atoms close to Io.