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研究生: 洪肇伶
Hung, Chao-Ling
論文名稱: 極低光度原恆星核DCE065之化學與動力學性質研究
Chemical and dynamical properties of a Very Low Luminosity Object - DCE065
指導教授: 賴詩萍
Lai, Shih-Ping
口試委員:
學位類別: 碩士
Master
系所名稱: 理學院 - 天文研究所
Institute of Astronomy
論文出版年: 2010
畢業學年度: 98
語文別: 英文
論文頁數: 36
中文關鍵詞: 恆星形成棕矮星
外文關鍵詞: star formation, brown dwarf
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  • 我們使用次毫米波陣列望遠鏡(Submillimeter Array)以及其他無線電望遠鏡來觀測一個極低光度原恆星核-DCE065,並研究它的化學與動力學性質。從熱連續譜與N2D+的分子譜線結果,我們發現生成DCE065的分子雲核的質量約為0.24個太陽質量,它的形狀則成扁平的橢球形狀。從N2D+的分子譜線中,我們偵測到一個延著橢球長軸的微小速度梯度,假設此速度梯度為分子雲核的轉動所造成,其轉動動能並不足以支撐分子雲核的重力位能。分析N2D+,N2H+與CO的分子譜線,我們發現DCE065的N2D+/N2H+豐度比例約為0.1左右,比許多典型的Class 0原恆星都來的高。另外,在靠近原恆星核中央處,我們沒有偵測到13CO與C18O分子,也沒有發現N2D+分子有減少的情形。這些化學性質都代表著DCE065是相當年輕以及相當冷的,也說明DCE065並不是處在很激烈的吸積過程中,或是他已經離開激烈吸積過程很久了。在12CO分子譜線的位置與速度關係圖中出現了一個紅移的三角型特徵,這樣的特徵可以被解釋為向外擴張的運動。我們估算這個向外擴張物質的質量,動量與能量,並發現DCE065的這些物理性質與其他在Perseus分子雲中較低能量的噴流相似,我們推測DCE065的紅移三角型特徵可能是由DCE065的噴流造成的。
    因為DCE065的分子雲核質量十分低,如果它現在的吸積速度高於每年3 X 10-8個太陽質量,我們估計它可能只能形成棕矮星而非一般低質量恆星。DCE065所呈現的極年輕化學性質與可能的噴流活動也支持了棕矮星可由類似低質量恆星的形成方式從分子雲核的塌縮所形成。


    We study the chemical and dynamical properties of a very low luminosity object - DCE065 using the Submillimeter Array and complementary single dish observations. The continuum and N2D+ emission show that DCE065’s parent core with a mass of 0.24 M☉ is in flattened structure. A small velocity gradient along the major axis of the N2D+ disk is marginally detected, suggesting that the rotational energy alone is insufficient to support the parent core. The very young and cold chemical features are evidenced by the high N2D+/N2H+ abundance ratio of 0.1, non-detection of CO evaporation in the central region and a constant N2D+ abundance profile. These features suggest that DCE065 may not have experienced a strong accretion phase or it has already left the burst accretion phase for a long time. The 12CO emission shows a
    large red shifted triangle feature in the PV diagrams which can be explained with an outward motion. Since the mass, momentum and energy of the expanding material are similar to those of the less energetic outflows in Perseus, the origin of the outward motion signature shown in the 12CO emission is probably due to outflow activities.
    Because the parent core mass is very low, DCE065 may destined to form a brown dwarf if its current accretion rate is higher than 3 × 10−8 M☉ yr−1. The young chemical features and possible outflow activities shown in DCE065 support the scenario that a brown dwarf forms from collapsing processes similar to typical low mass stars.

    1 Introduction 1 2 Observations 4 2.1 Submillimeter Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Conplementary single dish observations . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.1 Submillimeter Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.2 Arizona Radio Observatory 12 Meter Telescope . . . . . . . . . . . . . . 6 2.2.3 JCMT SCUBA archival data . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.4 JCMT HARP data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Results 7 3.1 Continuum emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 N2D+ and N2H+ emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2.1 ARO 12M N2H+ and SMT N2D+ detection . . . . . . . . . . . . . . . . . 10 3.2.2 SMA N2D+ detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 i 3.3 CO emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.3.1 SMT CO (J=2-1) detection . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.3.2 HARP 12CO (J=3-2) detection . . . . . . . . . . . . . . . . . . . . . . . 16 3.3.3 SMA CO (J=2-1) detection . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.3.4 Position-Velocity diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . 20 4 Discussion 25 4.1 Chemical properties of DCE065 . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.2 Envelope kinematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.3 The nature of DCE065 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5 Conclusion 33

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