Studies on the Distribution of Sources of Jovian Magnetospheric Plasma Originated from Io Based on Optical Observations

1.由28cm口径反射望远镜、干涉滤光片和电致冷CCD相机组成的观测系统。该系统的可探测发射强度小于10瑞利，足以有效探测火山气体排放。该系统已成为可能的二维分布的中性钠（NaI）和电离硫（SII）的气体与CCD成像的视野面积高达近40木星半径。2.观测的火山气体排放的观测已经在山。藏王，宫城，和爱丽丝泉，澳大利亚。为了获得更高的空间分辨率，我们利用日本国立天文台冈山91厘米口径反射望远镜进行了临时观测。特别是在澳大利亚，在近两周的时间里，几乎每天晚上都成功地进行了观测。3.观测结果在距木星20个木星半径范围内的较远区域观测到NaI气体的南北不对称空间分布。根据观测结果对气体释放过程进行了模拟，结果表明，这种不对称性不能用以往研究中提出的等离子体电荷交换引起的气体释放过程来解释。证实了在从几天到一周的时间尺度上，木卫一等离子体环的SII气体的发射强度在三个因子上变化。这些结果对于揭示木星磁层等离子体主要来源火山气体的释放过程和特征变化具有重要意义。

1.Developement of the Optical Observation System of Volcanic Gases Originated from IoThe observation system consists of a 28cm diameter relfecting telescope, interference filters, and an electric-cooling CCD camara. The detectable emission intensity of the system is less than 10 Rayleighs, which is effective enough to detect the volcanic gas emissions. The system has made possible to detect 2D distribution of neutral sodium (NaI) and ionized sulfer (SII) gases with the view area up to nearly 40 Jovian radii with a CCD imaging.2.ObservationsThe observations of volcanic gas emissions have been made at Mt.Zao, Miyagi, and at Alice Springs, Australia. The observation using the 91cm diameter reflecting telescope of the National Astronomical Observatory at Okayama, has been carried out temporaraily to make the observation with higher spatial resolution. In particular, in Australia, the observations have been successfully made almost every night during nearly two weeks. The data of temporal and spatial variations of the volcanic gases have been acquired through this unprecedented successive observation.3.Observation ResultsA north-south asymmetry of spatial distribution of NaI gas has been detected at a distant area out of 20 Jovian radii from Jupiter. As the result of the simulations of gas release process based on the observation result, it is concluded that the asymmetry cannot be interpreted by the gas release process caused by the charge exchange of isotropically distributed plasma which has been proposed in previous researches. It is confirmed for SII gas of the Io plasma torus that the emission intensity has varied at a foctor of three in the time scale of days to a week. These results are important for revealing little known gas release process and characteristic variations of the volcanic gases as the main source of Jovian magnetospheric plasma.