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題 名 | Probing the Magnetic Field Structure in Star-forming Regions through Molecular Line Polarization=藉由分子譜線偏振探測恆星形成區內的磁場結構 |
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作 者 | 楊智軒; 賴詩萍; | 書刊名 | 臺北天文館學報 |
卷 期 | 8 2010.12[民99.12] |
頁 次 | 頁24-28 |
分類號 | 323.8 |
關鍵詞 | 分子譜線; 偏振; 恆星; 磁場結構; |
語 文 | 英文(English) |
中文摘要 | 一般藉由觀測塵埃偏振來測量磁場的主要問題是無法分辨視線方向上的磁場結構。然而由於每道分子躍遷都有其特定的臨界濃度,因此測量分子譜線的偏振-Goldreich-Kylafis 效應(GK效應)-提供了一種獨特的方法來探測恆星形成區核心的三維結構。儘管目前很難觀測到GK效應,阿塔卡瑪大型毫米及次毫米波陣列(ALMA)將很有機會執行GK效應的觀測。為了要探討使用ALMA來觀測GK效應的可行性,我們開發了一套軟體來計算分子譜線在均勻磁場及速度梯度下的偏極化。此程式藉由大速度梯度近似,解出多躍遷輻射傳輸方程式在平行和垂直磁場方向的解,並預測每個躍遷的偏振百分比及方向。這裡我們展示在不同溫度、速度梯度幾何結構和分子雲密度的情況下,一氧化碳(CO)、一硫化碳(CS)及一氧化矽(SiO)等分子在高能階躍遷的結果。藉由這個軟體,我們將可以估計使用ALMA探測磁場幾何形狀時特定躍遷的偏極化量值。 |
英文摘要 | The major problem of the most commonly used method for probing magnetic fields, the dust polarization observation, is that it is incapable of differentiating the field structure along the line of sight. Since every molecular transition has a particular critical density, measuring the molecular line polarizations, the Golreich-Kylafis effect (GK effect), provides a unique way to probe the three-dimensional structure in star-forming cores. Although currently it is very difficult to measure GK effect, the Acatama Large Millimeter/submillimeter Array (ALMA) will potentially enable routine observations of GK effect. In order to investigate the feasibility of the GK effect observations with ALMA, we develop a computer program for modeling molecular polarization with uniform magnetic field and velocity gradient. The program solves the radiative transfer equations for multiple transitions in the direction parallel and perpendicular to the magnetic field under the large velocity gradient approximation, and predicts the polarization percentage and direction of every transition. Here we demonstrate the results for CO, CS and SiO molecules in high-level transitions at different temperature and with different velocity gradient geometry and molecular cloud density. With this program, we can estimate the polarization of specific molecular transition for probing the magnetic field geometry with ALMA. |
本系統中英文摘要資訊取自各篇刊載內容。