Millimeter and Submillimeter Observations of Barnard 1-bN and Barnard 1-bS

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姓名

劉芳君(Fang-Chun Liu) 查詢紙本館藏

畢業系所

天文研究所

論文名稱

(Millimeter and Submillimeter Observations of Barnard 1-bN and Barnard 1-bS)

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摘要(中)

我們利用多波段觀測來研究兩個在巴納德星雲的毫米/次毫米天體，他們的名稱是Barnard 1-bN和Barnard 1-bS。從這兩個天體所發出的塵埃連續輻射訊號，我們發現他們物質分布很緻密，且物質本身相當低溫（塵埃溫度10-16 K）。Spitzer的MIPS望遠鏡所拍出的24和60微米波段影像裡，這兩個天體並沒有被偵測到，這表示他們還包裹在雲深處。由SMA觀測的CO（J=2-1）譜線資料顯現出Barnard 1-bS有噴流，Barnard 1-bN則是疑似有噴流。這些噴流都不是很大（大約2000 AU大小）。這個結果指出這兩個天體已經蘊含著Class 0原恆星。另一方面，這兩個天體的化學特性反而相似於前恆星核：N2D+（J=3-2）譜線訊號很強而且和塵埃連續輻射訊號的分布很一致。反之，H13CO+（J=1-0）譜線訊號則很微弱，甚至是沒有偵測到。這樣的化學特性可能是因為在低溫高密度環境中，H13CO+ 分子已經分解附著在塵粒上所導致。而這樣子的化學特性是相似於前恆星核的化學特性。因此，綜合我們所發現的這兩個天體的物理及化學特性，我們可以知道Barnard 1-bN和Barnard 1-bS是在恆星形成非常早期的天體，他們的演化時期可能正好落在前恆星核時期與Class 0原恆星時期中間。

摘要(英)

The physical and chemical properties of two mm/sub-mm sources in Barnard cloud, Barnard 1-bN and Barnard 1-bS, are studied with multi-wavelength observations. The dust continuum from these two sources shows spatially compact distribution and very cold spectral energy distributions (T$_{dust}$=10--16 K). These two sources have no mid-IR counterpart in the Spitzer MIPS 24 and 60 micron bands, indicating that they are deeply embedded. The CO J=2--1 data obtained with the SMA suggest that B1-bS and probably B1-bN are associated with the compact ($sim$ 2000; AU size) molecular outflows. These results suggest that Barnard 1-bN and Barnard 1-bS are already harboring Class 0 protostars. On the other hand, the chemical properties of these two sources are similar to those of pre-stellar cores: the N$_2$D$^+$ J=3--2 emission is strong (0.3 K for B1-bN and 0.1 K for B1-bS) and clearly traces the two compact sources, while the H$^{13}$CO$^+$ J=1--0 emission is weak or barely detected near or at the continuum peaks. This lack of H$^{13}$CO$^+$ emission is probably due to the depletion of the H$^{13}$CO$^+$ molecule onto the grain under the condition of low temperature and high density, as in the case of pre-stellar cores. The observed physical and chemical properties suggest that B1-bN and B1-bS are in the very beginning stage of protostellar evolution, probably in the evolutionary stage between pre-stellar core and class 0 source.

關鍵字(中)

★ 恆星形成
★ 原恆星

關鍵字(英)

★ star formation
★ Class 0
★ protostar
★ prestellar core

論文目次

1 INTRODUCTION 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Dark Cloud Barnard 1 . . . . . . . . . . . . . . . . . . . . . . 4
2 OBSERVATIONS AND DATA REDUCTION 7
2.1 Single-dish observations . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 Dust continuum . . . . . . . . . . . . . . . . . . . . . . 7
2.1.2 H13 CO+ mapping . . . . . . . . . . . . . . . . . . . . . 9
2.1.3 1.3 mm observations with the SMT . . . . . . . . . . . 9
2.2 Millimeter-interferometer observations . . . . . . . . . . . . . 10
2.2.1 3 mm observations with the NMA . . . . . . . . . . . . 10
2.2.2 1.3 mm observations with the SMA . . . . . . . . . . . 11
3 RESULTS 15
3.1 Dense gas distribution in B1 . . . . . . . . . . . . . . . . . . . 15
3.2 Two continuum sources in B1-b . . . . . . . . . . . . . . . . . 18
3.3 Molecular Line emission . . . . . . . . . . . . . . . . . . . . . 27
3.3.1 N2 D+ J =3–2 Line Emission . . . . . . . . . . . . . . . 27
3.3.2 H13 CO+ J =1–0 Line Emission . . . . . . . . . . . . . . 35
3.3.3 12 CO J =2–1 Line Emission . . . . . . . . . . . . . . . 36
3.3.4 13 CO J =2–1 and C18 O J =2–1 Line Emission . . . . . 41
4 DISCUSSIONS 45
4.1 The evolutionary stages of Barnard 1-bN and Barnard 1-bS . . 45
4.1.1 Physical properties and Outﬂow activities of B1-bN
and B1-bS . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.1.2 Possible depletion of H13 CO+ molecule in the dense gas
envelope . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.1.3 Chemical properties of B1-bN and B1-bS . . . . . . . . 51
4.2 The diﬀerence of the evolutionary stage between Barnard 1-bN
and Barnard 1-bS . . . . . . . . . . . . . . . . . . . . . . . . . 53
5 SUMMARY 55
A Combining Single-Dish and Interferometer data 62
A.0.1 Dealing with 45m Data . . . . . . . . . . . . . . . . . . 65
A.0.2 Combined the 45m Data and the NMA data to make
image . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
B Column Density and Mass Calculation 68

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指導教授

平野尚美、陳文屏
(Naomi Hirano、Wen-Ping Chen)

審核日期

2009-7-22

推文