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研究生： 沈孟嫺
Shen, Meng-Hsien
論文名稱： 分子雲面狀結構之塌縮與穩定分析
Collapse and Stability Analysis of Sheet-like Structures in the Molecular Cloud
指導教授： 李悅寧
Lee, Yung-Ning
學位類別： 碩士
Master
系所名稱： 地球科學系
Department of Earth Sciences
論文出版年： 2020
畢業學年度： 108
語文別： 英文
論文頁數： 36
中文關鍵詞： 恆星形成 、星際介質 、絲狀體 、集中絲狀體系統 、前恆星核 、流體力學 、自相似解 、微擾分析
英文關鍵詞： Star formation, Interstellar medium (ISM), Filament, Hub-filament system, Prestellar core, Hydrodynamics, Self-similar solution, Perturbative analysis
DOI URL： http://doi.org/10.6345/NTNU202001007
論文種類： 學術論文
相關次數： 點閱：142  下載：15 
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    • 恆星形成發生在分子雲內的高密度區域，近年來的觀測發現分子雲裡普遍存在絲狀結構 (filamentary structure)，並且與前恆星核 (prestellar core) 形成有高度相關。Monocerous R2 (Mon R2) 分子雲區域的觀測資料呈現有類似面狀的結構 (sheet-like structure)，並且有數條的絲狀體 (filament) 往中心匯聚。我們的研究是想用物理模型來了解這種面狀結構的動力機制及其演化過程。我們考慮在其自身重力下 (self-gravity)，這個片狀結構的徑向塌縮動態，並解其自相似解 (self-similar solution)。我們畫出表面密度與速度的徑向剖面圖和Mon R2的觀測值做比對。接著我們使用微擾分析 (perturbative analysis) 研究絲狀體在這種結構下的發展，並比較生成絲狀體的速率與大尺度時間下塌縮的速率，並得到絲狀體的特徵數量與每條絲狀體的線質量密度。

    Star formation occurs inside over-dense regions in molecular clouds. In recent years, observations have found filamentary structures in molecular clouds, which are highly associated with the prestellar cores. Observation of the Monocerous R2 region (Mon R2) suggests a sheet-like structure and shows a structure with several filaments converging into the central hub. We study the dynamics of this sheet-like structure and its evolution with a physical model. We consider the radial collapse of a sheet under self-gravity and solve the self-similar solutions. We produce surface density and velocity profiles which are compatible with observations of Mon R2. Finally, we study the development of filaments in this structure using perturbative analysis. By comparing the timescales of the filament growth rate and the global collapse, it will allow to obtain the characteristic number of filaments and the line mass of each filament.

    中文摘要 i Abstract iii contents vi List of Figures vii 1 Introduction 1 1.1 Star formation and the interstellar medium 1 1.2 Fluid dynamics 5 1.3 CollapseCriterion 7 1.3.1 Sphere(γ<4/3) 7 1.3.2 Cylinder(γ<1) 7 1.4 Self-similar solution: example of a spherical collapse 8 1.4.1 Physical equation 8 1.4.2 Similarity solution 9 2 Collapse solution of a self-gravitating sheet 11 2.1 Thin sheet approximation 11 2.1.1 Vertical equilibrium 11 2.1.2 Radial collapse equations 12 2.1.3 Collapse criterion γ<4 13 2.2 The equation set of self-similar collapse 14 2.3 Treatment of self-gravity in a flat system 15 2.3.1 Monopole approximation 15 2.3.2 Exact gravitational field from the surface density 16 2.4 Mathematical analysis 18 2.4.1 The sonic line 18 2.4.2 Classification of sonic line 18 2.4.3 Eigensolutions through a sonic point 19 2.4.4 Asymptotic solutions 19 2.5 Numerical solution 22 2.5.1 Monopole approximation 22 2.6 Physical domain 23 3 Perturbative analysis 27 3.1 Formulation 27 3.2 Treatment of self-gravity in a flat system 30 3.2.1 Approximation from local surface density 30 3.2.2 Exact gravitational field from the surface density 30 4 Discussion and conclusions 33 Bibliography 35

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