Envelope Structure of Deeply Embedded Young Stellar Objects in the Serpens Molecular Cloud
Envelope Structure of Deeply Embedded Young Stellar Objects in the Serpens Molecular Cloud
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巨蛇分子云中深埋年轻恒星的包膜结构
DOI：
10.1086/306844
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
G. Blake
中科院分区：
文献类型：
--
作者：
M. Hogerheijde;E. V. van Dishoeck;J. Salverda;G. Blake
双折射合成和单碟（亚）毫米分子线和连续谱观测非常详细地揭示了深埋在致密的恒星形成巨蛇座分子云中的年轻恒星天体（SMM 1 = FIRS 1，SMM 2，SMM 3，SMM 4）的包络结构。SMM 1、3和4显示了欧文斯谷毫米波阵列光束在λ=3.4-1.4 mm处的部分分辨（>2“=800 Au）连续辐射。连续辐射精确地限制了包络中的密度结构，这可以用径向幂律描述，斜率为-2.0 0. 5，尺度为300至8000 Au。对于SMM 1、3和4，在8000 Au半径内推断的包封质量分别为8.7、3.0和5.3 M。需要一个在1.1 mm处占总通量20%-30%的点源来拟合长基线上的观测结果，对应于~100 Au或拱星盘内的温暖包层物质。没有连续发射被检测到的SMM 2，对应的上限为0.2 M假设Td=24 K。没有任何致密尘埃的排放表明SMM 2的核心不包含一个中央原恒星。13 CO，C18 O，HCO+，H13 CO+，HCN，H13 CN，N2 H + 1-0，SiO 2-1和SO 22-11跃迁的衍射合成观测显示了SMM 1，3和4的紧凑发射。SMM 2只显示了一些散布在主视野中的团块，支持了这个核心不包含中心星星的结论。SMM 1、3和4周围的致密分子发射迹线为5“-10”“（2000-4000 Au）直径的核心，对应于包膜的致密区域，以及与分子流出直接相关的物质。特别突出的是光学厚HCN和HCO+线，它们沿流出腔的壁沿着明亮地显示。SO和SiO痕量激波物质，其丰度可能比暗云值增加1-2个数量级。詹姆斯·克拉克麦克斯韦和加州理工学院的亚毫米望远镜在230、345、490和690 GHz的大气窗口观测到了总共31个分子跃迁，它们指向所有四个源，其中包括CO、HCO+、HCN、H2 CO、SiO、SO及其同位素。这些谱线显示出20-30 km s-1宽的线翼、深而窄（1-2 km s-1）的自吸收和2-3 km s-1的半高宽线芯。高激发线如12 CO 4-3和6-5，13 CO 6-5和几个H2 CO跃迁的存在表明存在温度为100 K的材料。分子激发和谱线转移的Monte Carlo计算表明，由尘埃辐射导出的包络模型能成功地再现观测到的谱线强度。冷气体中CO的消耗与NGC 1333 IRAS 4等天体中推断的值相比是适度的，这表明整个包层的大消耗阶段是短暂的，可能受到当地星星形成密度的影响。CO和H2 CO的高激发谱线的发射需要少量~100 K的物质的存在，所述~100 K的物质占包层总质量的不到1%，并且可能与包层的流出或最内部区域相关联。在温暖的（Tkin>20 K）包层中推导出的分子丰度与其他0类YSO（如IRAS 16293-2422）中发现的分子丰度相似，尽管一些物种似乎在SMM 1中增强。总之，所提出的观测和分析提供了第一个全面的看法，信封的物理和化学结构的深嵌入年轻恒星物体在集群环境中的规模在1000和10,000 Au。
Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2″=800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at λ=3.4-1.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0±0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 M☉ for SMM 1, 3, and 4, respectively. A point source with 20%-30% of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within ~100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 M☉ assuming Td=24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the 13CO, C18O, HCO+, H13CO+, HCN, H13CN, N2H+ 1-0, SiO 2-1, and SO 22-11 transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5''-10'' (2000-4000 AU) diameter cores that correspond to the densest regions of the envelopes, as well as material directly associated with the molecular outflow. Especially prominent are the optically thick HCN and HCO+ lines that show up brightly along the walls of the outflow cavities. SO and SiO trace shocked material, where their abundances may be enhanced by 1-2 orders of magnitude over dark-cloud values. A total of 31 molecular transitions have been observed with the James Clerk Maxwell and Caltech Submillimeter telescopes in the 230, 345, 490, and 690 GHz atmospheric windows toward all four sources, containing, among others, lines of CO, HCO+, HCN, H2CO, SiO, SO, and their isotopomers. These lines show 20-30 km s-1 wide line wings, deep and narrow (1-2 km s-1) self-absorption, and 2-3 km s-1 FWHM line cores. The presence of highly excited lines like 12CO 4-3 and 6-5, 13CO 6-5, and several H2CO transitions indicates the presence of material with temperatures ≳100 K. Monte Carlo calculations of the molecular excitation and line transfer show that the envelope model derived from the dust emission can successfully reproduce the observed line intensities. The depletion of CO in the cold gas is modest compared to values inferred in objects like NGC 1333 IRAS 4, suggesting that the phase of large depletions through the entire envelope is short lived and may be influenced by the local star formation density. Emission in high-excitation lines of CO and H2CO requires the presence of a small amount of ~100 K material, comprising less than 1% of the total envelope mass and probably associated with the outflow or the innermost region of the envelope. The derived molecular abundances in the warm (Tkin>20 K) envelope are similar to those found toward other class 0 YSOs like IRAS 16293-2422, though some species appear enhanced toward SMM 1. Taken together, the presented observations and analysis provide the first comprehensive view of the physical and chemical structure of the envelopes of deeply embedded young stellar objects in a clustered environment on scales between 1000 and 10,000 AU.
DOI：
10.1086/175915
发表时间：
1995-07
期刊：
The Astrophysical Journal
影响因子：
--
作者：
Ewine;-F.;Van Dishoeck;L. Geoffrey;-A.;Blake;David J. Jansen;T. Groesbeck
通讯作者：
Ewine;-F.;Van Dishoeck;L. Geoffrey;-A.;Blake;David J. Jansen;T. Groesbeck