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研究生： 彭之翰
Chih-Han Peng
論文名稱： 在不同均功參數下星團的擴散及核心的形成
Dispersal and core formation of stellar clusterswith different initial virial ratio
指導教授： 高仲明
Chung-Ming Ko
口試委員:
學位類別： 碩士
Master
系所名稱： 理學院 - 天文研究所
Graduate Institute of Astronomy
畢業學年度： 99
語文別： 英文
論文頁數： 45
中文關鍵詞： 動力學 、多體模擬 、均功參數 、星團
外文關鍵詞： evaporation, virial ratio, star cluster, N-body simulation
相關次數： 點閱：11  下載：0 
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    • 一般認為恆星通常成群誕生於分子雲之中，而分子雲的消散會對內部的初生星團產生動力學上的影響而導致初生星團的解離。在本論文中，假設當分子雲的消散速率極高時，殘留下來之星團的均功參數（即星團動能與位能絕對值之比值）會大於0.5，我們用多體模擬來研究均功參數較高（>0.5）的星團的演化過程以及利用三維動力學資料去定義星團的質量流失。根據模擬的結果我們發現,初始均功參數大於0.6時星團開始產生質量流失，而均功參數大於1.42的星團則完全解散。易言之，即使系統總能大於零（及均功參數大於1），星團也未必會完全解散而可能會形成一個穩定的”核心”。此核心的形成時間在初始均功參數小於1.2時變化不大，而超過1.2之後形成時間會明顯變長。

    It is believed that most stars form in groups inside molecular clouds. When the natal cloud is dispersed, the embedded stellar group may dissolve into field stars. We use the code NBODY2-Hermite to do numerical experiments to study the behavior of stellar groups in the case when the cloud dispersion rate is very high. In general the stellar group has a virial ratio larger than one half initially. We performed a series numerical experiments on clusters with different initial virial ratios (virial ratio = Q from 0.5 to 1.69) for clusters with Q from 0.6 to 1.41 the outer part of the cluster is dispersed but a core remains, for Q > 1.42 the whole cluster is destroyed. Even if the total energy of the whole system is positive (Q > 1), it is possible that the cluster is not disrupted completely and a stable core can be formed. The formation time of stable core is more and less the same for Q < 1.2. For Q > 1.2 the formation time of the stable core increase rapidly with Q.

    1. Introduction 1 1-1 Stellar Cluster.....................................1 1-2 N-Body Simulation...................................1 1-3 Effect of Molecular Cloud and Virial Ratio..........2 1-4 Evolution of Clusters with different Virial Ratio...4 2. Code and Simulation 5 2-1 NBODY2-Hermite......................................5 2-1-1 Input and Output..................................6 2-1-2 Units............................................10 2-2 Initial Condition..................................11 2-2-1 Model of Stellar Clusters........................11 2-2-2 Virial Ratio.....................................11 3. Results 12 3-1 Evolution of Cluster with different Virial Ratio...12 3-1-1 Space distribution...............................12 3-1-2 Lagrangian Radii.................................13 3-2 Definition of Mass Loss............................14 3-2-1 Method 1 : Radial Velocity.......................14 3-2-2 Method 2 : Free of Interaction...................18 3-2-3 Method 3 : Virial Equilibrium....................22 3-2-4 Method 4 : R-V Diagram...........................25 3-3 Virial Ratio and Mass Loss.........................29 3-4 Core Formation.....................................30 4. Summary 33 References 34

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