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研究生:慶道沖
研究生(外文):Ching, Tao-Chung
論文名稱:從陣列望遠鏡偏極化觀測模擬原恆星核的磁場結構
論文名稱(外文):Modeling Magnetic Fields in Protostellar Cores from Interferometric Polarization Measurements
指導教授:賴詩萍
指導教授(外文):Lai, Shih-Ping
口試委員:呂聖元李景輝
口試日期:2011-7-31
學位類別:碩士
校院名稱:國立清華大學
系所名稱:天文研究所
學門:自然科學學門
學類:天文及太空科學學類
論文種類:學術論文
論文出版年:2011
畢業學年度:99
語文別:中文
論文頁數:54
中文關鍵詞:恆星形成區磁場
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  • 被引用被引用:0
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  • 下載下載:11
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In this thesis, I present the results using two methods to model the magnetic fields in protostellar cores with interferometric polarimetry. I compare high angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A with empirical models of density profiles and magnetic fields in protostellar core. With the assumptions of uniform temperature distribution, constant dust property, and small dust alignment efficiency, the simulations of Stokes I, Q, and U maps are computed with integrals along the line-of-sight. The Stokes I, Q, and U maps are then convolved into visibilities of Stokes parameters to be compared with observations using two methods. The first method of modeling magnetic fields is based on the comparisons of modeled polarization angle and observed polarization angle. The second method is a direct analysis of Stokes parameter visibilities from models and observations. Three types of magnetic field configurations, poloidal magnetic fields, inclined poloidal magnetic fields, and polodial and toroidal magnetic fields, are used to model the polarization distribution in IRAS 4A. The results show that hourglass structures alone cannot reproduce the depolarization effect in IRAS 4A if the inclination angle is indeed as small as what have been inferred from the outflow line-of-sight velocity and proper motions. My analysis favors a morphology of inclined magnetic fields with an hourglass structure at scales of few hundred AU and a toroidal component with a maximum in a middle section of the disk around the protostars. Applications of the modeling magnetic fields in the visibility space to high quality interferometric polarization measurements and detail studies with magnetohydrodynamics (MHD) simulations would be feasible in the future.
Contents

1 Introduction 1

2 Observations and Data Analysis 6

3 Methods 10
3.1 Density Distribution 11
3.2 Magnetic Field Structure 11
3.3 Stokes Parameters 13
3.4 Fitting Density Models 15
3.5 Fitting Magnetic Field Models 17
3.5.1 Method A 18
3.5.2 Method B 20

4 Results 21
4.1 Plummer-like Density Models 21
4.2 Magnetic Field Models from Method A 22
4.2.1 Poloidal Magnetic Fields 22
4.2.2 Poloidal and Toroidal Magnetic Fields 23
4.3 Magnetic Field Models from Method B 24
4.3.1 Poloidal Magnetic Fields 24
4.3.2 Poloidal Magnetic Fields with Inclination 25

5 Discussion 27
5.1 Hourglass Structure 27
5.2 Polarization Hole 28
5.3 The Magnetic Field Structure in IRAS 4A 29
6 Conclusion 31


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