本計畫利用地面望遠鏡對埃歐的鈉雲噴流進行低色散與高色散光譜以及影像的觀測， 並建立一考慮周嚴的鈉噴流模型，從理論方面與實際的觀測資料做比對的工作。 我們在2000年底，Cassini號太空船近距離觀測埃歐的同時， 利用北京天文台的2.16米望遠鏡搭配低色散光譜儀，同步地對埃歐鈉噴流進行徑向結構的觀測， 其結果與G. Cremonese等人(1992)的觀測資料比較後，得到近似的結果。 除此之外，本論文中的鈉噴流模型，採用A. Kopp(2001)的MHD模型詳細地描述鈉噴流粒子的速度分佈情形， 以及利用N. M. Schneider等人(1991a)所觀測之埃歐大氣密度分佈來描述電荷交換產生鈉噴流粒子的機率分佈， 並將結果分別與C. Pilcher等人(1984)的觀測做形態幾何結構的比較， 以及與G. Cremonese等人(1992)的觀測做鈉噴流粒子之速度分佈的比較。其結果顯示， 鈉噴流粒子在埃歐面向木星半球之後半部，產生的機率較低，此結果正符合J. K. Wilson等人(1999)所提出的理論。 未來，我們將利用中央大學鹿林前山天文台之76公分望遠鏡結合自製的Coronagrapher，進行鈉噴流與IPT之影像觀測。 同時，與北京天文台合作，利用高色散的光譜儀，研究粒子速度分佈等更細微之結構， 以其更進一步的瞭解埃歐大氣與離子球層的結構及與IPT交互作用的問題。 In this thesis work the production and morphology of Io's sodium cloud have been studied using both low- and high-spectral resolution spectroscopic data and filter-images. In addition, detailed numerical models have been constructed to provide theoretical comparison to the observations. During the Jupiter Flyby of the Cassini spacecraft in December 2000 enroute to the Saturnian system, the 2.16 m spectrograph of the Beijing Astronomical Observatory (BAO) was used for simultaneous ground-based coverage of Io's sodium cloud emission. In comparision with the work of Cremonese et al. (1992), the spatial distribution of the sodium D-line brightness deduced in one particular orbital time interval was consistent with the presence of a fast atomic sodium jet. We have used the Io interaction model from the magnetohydrodynamic computations by Dr. Andreas Kopp (2001) to describe the velocity flow field in the vincinity of Io. Furthermore, the number density profile of sodium atoms derived by Schneider et al. (1991a) was adopted in a Monte Carlo code to simulate the production and velocity distribution of fast neutral sodium atoms created by charge exchange effect of the sodium ions. The theoretical patterns of the fast sodium jets were compared with the observed morphologies obtained by C. Pilcher (1984) and the two-dimensional spectrographs of Cremonese et al. (1992). Our results suggested that the fast sodium atoms should have higher production on the trailing side of the anti-Jupiter hemisphere. This is in general agreement with the conclusion of Wilson et al. (1999). For future work, we plan to use a home-made coronagrapy mated to the 76-cm Super Light Telescope at the Lulin Observatory to monitor the time variabilities of the sodium jets and the Io plasma torus. We also want to continue our cooperative efforts with BAO to obtain high-spectral resolution data. The applications of our theoretical model to these observations will bring important insight to our understanding of the structures of Io's atmosphere and ionosphere and their electrodynamical interactions with the Jovian magnetosphere.
