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研究生： 謝天晧
Hsieh, Tien-Hao
論文名稱： 早期階段的原恆星以及原始棕矮星: 極暗原始恆星研究
The early phase of protostars and proto-brown dwarfs: Studies of Very Low Luminosity Objects (VeLLOs)
指導教授： 賴詩萍
Lai, Shih-Ping
口試委員: 平野尚美
Hirano, Naomi
李景輝
Lee, Chin-Fei
呂聖元
Liu, Sheng-Yuan
高見道弘
Takami, Michihiro
江瑛貴
Jiang, Ing-Guey
學位類別： 博士
Doctor
系所名稱： 理學院 - 天文研究所
Institute of Astronomy
論文出版年： 2015
畢業學年度： 104
語文別： 英文
論文頁數： 134
中文關鍵詞： 恆星形成 、星際介質 、棕矮星
外文關鍵詞： star formation, interstellar medium, brow dwarf
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    • 本篇論文的目標在於研究新生的低質量原恆星以及棕矮星的特性。史匹哲太空望遠鏡發現一種新型原始恆星，其中心光度低於0.1個太陽光度，稱為極暗原始恆星 (Very Low Luminosity Objects, VeLLOs)。這樣的低亮度極有可能源自於一個亞恆星天體，而一般認為這個亞恆星天體是一個非常早期的原恆星或是原始棕矮星。此外，對極暗原恆星而言，恆星形成中吸積過程所產生的亮度也遠低於其他原恆星。因此，普遍認為極暗原恆星是處於一個暫停吸積的狀態。本論文共分四個部分：
    第一部分，我們發明了一種方法來找出更多低亮度的原恆星。將我們的方法運用於公開的史匹哲太空望遠鏡資料，我們在五個較近的分子雲中找到了322個新的相對較暗的原恆星，增加了大約28％的原恆星數量。
    第二部分，我們深入研究十五個中心光度低於0.2個太陽光度的暗原恆星。我們發現他們的化學以及動力性質彼此間有相當大的變化，但大多數符合較年輕原恆星的特性。
    第三部分，我們從我們的樣本中，挑出一顆相當特別的極暗原恆星，IRAS 16253--2429，從更深入的原恆星噴流研究中，發現它極有可能是正在形成中的原始棕矮星雙星系統。
    第四部分，我們使用紅外線加法夏望遠鏡觀測了二十顆暗原恆星，加上史匹哲資料，我們發現十二個紅外線波段的原恆星雙極噴流。我們並發現雙極噴流的張角，與以前的研究相符，會隨著原恆星演化而增加。

    My thesis project aims at understanding the natures of low mass protostars and proto-brown dwarfs at early evolutionary stage. A new category of Young Stellar Objects (YSOs), Very Low Luminosity Objects (VeLLOs), are newly discovered and defined by their low internal luminosity (Lint<0.1Lsun). The low luminosity infers that VeLLOs host a substellar mass central object at the present time and thus can be interpreted as a very young protostar or low mass protostar. This low luminosity also provides a constraint on their accretion luminosity as well as the accretion rate, suggesting VeLLOs are at a quiescent accretion phase. This thesis consists of four papers:
    (i) For the first paper, we develop a new identification method of YSOs to identify faint protostars in order to find more VeLLOs. Applying this method to the Spitzer archival data in five nearby molecular clouds, we identify 322 (28%) new YSO toward the lower end of the luminosity function compared with previous works. Based on this method, we further find seven VeLLOs in these molecular clouds.
    (ii) We study the chemical and dynamical properties of 15 selected Low Luminosity Objects (Lint<0.2Lsun) through molecular line emissions at millimeter/submillimeter wavelengths. We found that LLOs could have wide variety in their parent cores and tend to be at an very early evolutionary stage.
    (iii) We present a detailed investigation on the protostellar outflow driven by a unique VeLLO, IRAS 16253--2429. Our results suggest that IRAS 16253--2429 is very likely a proto-brown dwarf binary system.
    (iv) Using CFHT, we make an infrared outflow survey toward 20 LLOs. The outflows are detected in 12 LLOs (including 4 from Spitzer) and the outflow opening angles are widening as the core evolves as expected.

    Contents 1 Introduction 1 2 Populations of Young Stellar Objects in Nearby Molecular Clouds 3 2.1 INTRODUCTION ............................ 3 2.2 DATA................................... 6 2.2.1 c2dData.............................. 6 2.2.2 SWIREData ........................... 8 2.3 YSOIDENTIFICATION......................... 8 2.3.1 SelectionProcess ......................... 8 2.3.2 Multi-D Array Construction and Galaxy Probability Calculation 9 2.3.3 GiantStarContamination .................... 15 2.3.4 AdvantagesofMulti-DMethod ................. 16 2.4 RESULT:NEWYSOcLIST....................... 17 2.4.1 AnalysisofTheNewlyIdentifiedYSOc . . . . . . . . . . . . . 17 2.4.2 MissedorExcludedYSOcfromThec2dLists . . . . . . . . . 22 2.4.3 PAHEmission........................... 26 2.4.4 Uncertainty From The Selections of Bands for The Two 5-D arrays ............................... 26 2.5 DISCUSSION............................... 27 2.5.1 NewYSOIdentificationMethodandResults . . . . . . . . . . 27 2.5.2 Newly Identified Very Low Luminosity Object (VeLLO) Can- didates............................... 28 2.5.3 StatisticalProperties....................... 29 2.6 SUMMARY................................ 33 3 Properties of the Molecular Cores of Low Luminosity Objects 37 3.1 INTRODUCTION ............................ 37 3.2 OBSERVATIONS............................. 40 3.2.1 Sample............................... 40 3.2.2 KittPeak12mTelescopeobservations . . . . . . . . . . . . . 41 3.2.3 SMTobservations......................... 41 3.3 RESULTS................................. 42 3.3.1 N2H+andN2D+ ......................... 42 3.3.2 HCO+andHCNobservations .................. 44 3.4 ANALYSIS ................................ 45 i 3.4.1 N2H+Non-LTERADEXanalysis................ 45 3.4.2 N2D+/N2H+columndensityratio................ 49 3.4.3 Asymmetryparameters...................... 51 3.4.4 Two-layermodelfitting...................... 52 3.5 DISCUSSION............................... 53 3.5.1 The physical conditions from Non-LTE RADEX analysis . . . 53 3.5.2 N(N2D+)/N(N2H+) ratio as an age indicator . . . . . . . . . . 54 3.5.3 Infallindicators.......................... 56 3.6 CONCLUSION .............................. 58 3.7 Appendix ................................. 64 4 IRAS 16253–2429 (DCE 185): the First Proto-Brown Dwarf Binary Candidate Identified through Dynamics of Jets 67 4.1 INTRODUCTION ............................ 67 4.2 OBSERVATIONS............................. 70 4.2.1 SMAobservations......................... 70 4.2.2 JVLAobservations ........................ 70 4.2.3 IRAM30mCO(2–1)observations ............... 71 4.2.4 APEXCO(6–5)/(7–6)observations. . . . . . . . . . . . . . . 71 4.3 RESULTS................................. 72 4.3.1 Centralsource-SMAandJVLAimages . . . . . . . . . . . . 72 4.3.2 Jets/outflowsfromSMAobservations . . . . . . . . . . . . . . 73 4.3.3 Jets/outflows from IRAM 30m and APEX observations . . . . 75 4.4 ANALYSIS ................................ 76 4.4.1 Dynamical features of the molecular jets/outflows . . . . . . . 76 4.4.2 Physicalconditions........................ 83 4.5 Discussion................................. 89 4.5.1 Physicalpropertiesoftheoutflows . . . . . . . . . . . . . . . 89 4.5.2 Proto-browndwarfbinarycandidate . . . . . . . . . . . . . . 92 4.5.3 Massaccretion .......................... 94 4.6 Summary ................................. 97 4.7 Appendix-Originalmapsandchannelmaps. . . . . . . . . . . . . . . 104 5 Widening of Protostellar Outflows: an Infrared Outflow Survey in Low Luminosity Objects 107 5.1 INTRODUCTION ............................ 107 5.2 OBSERVATIONS............................. 108 5.2.1 Sample...............................108

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