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

1.放射性火山气体光学观测系统的研制该观测系统由直径28厘米的反射望远镜、干涉滤光片和电致冷的CCD摄像机组成。该系统的可探测发射强度小于10瑞利，足以探测到火山气体的排放。该系统能够探测中性钠(NaI)和电离硫磺(SII)气体的二维分布，视野范围可达近40木星半径，并可用CCD成像。2.观测在宫城县赵山和澳大利亚爱丽斯斯普林斯进行了火山气体排放的观测。为了使观测具有更高的空间分辨率，使用冈山国家天文台直径91厘米的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，几乎每晚都成功地进行了观测。通过这一史无前例的连续观测，获得了火山气体的时空变化数据。3.观测结果在距木星20木星半径的远处，探测到了NaI气体空间分布的南北不对称。根据观测结果对气体释放过程的模拟结果表明，前人提出的各向同性分布等离子体电荷交换引起的气体释放过程不能解释气体释放过程的不对称性。对于Io等离子体环的SiI气体，证实了发射强度在几天到一周的时间尺度上以三个因子的形式变化。这些结果对于揭示作为木星磁层等离子体主要来源的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.