An H13CO+ Survey for Dense Envelopes around Low-Mass Embedded Sources in Taurus
An H13CO+ Survey for Dense Envelopes around Low-Mass Embedded Sources in Taurus
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对金牛座低质量嵌入源周围致密包层的 H13CO 调查
DOI：
10.1086/318383
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
K. Sunada
中科院分区：
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作者：
M. Saito;R. Kawabe;Y. Kitamura;K. Sunada
利用野边山毫米波阵列（NMA）对金牛座10个低质量嵌入年轻源进行了稠密气体测量，以研究原恒星的演化。所有的源都是在高密度示踪剂H13 CO+（J = 1-0）谱线上观测到的。其中6个样品的H13 CO+排放量显著（≥4.5 σ）。H13 CO+的辐射线大致垂直于分子流出轴分布，这表明H13 CO+的辐射线追踪着与中心恒星相关的致密包层。结果表明，致密包层的大小和质量分别为（1-7）× 103 Au和0.01-0.2 M。根据NMA图上H13 CO+的强度，将这10个源分为以下三类，并利用我们自己的和其他现有的数据研究了它们的性质。A类源的H13 CO+发射集中在星星上，其延伸方向垂直于分子流出轴。这些源也有密集的外流气体和中央冷凝的母核。B类源在源位置附近有H13 CO+排放，并有密集的流出气体。然而，B类源周围的母核具有较浅的密度分布。C类源在稠密气体示踪剂中既没有H13 CO+发射，也没有机翼发射。根据这些性质，我们得出结论，低质量原恒星是通过耗散其母云核而从A、B类源演化到C类源的，这与广泛接受的星星形成的观点是一致的。此外，这些观测数据表明，显着分散的母核的分子外流和主要吸积阶段结束在早期的原恒星阶段。10个源中的6个在87 GHz的连续发射中被检测到。H13 CO+发射的强度与87 GHz处的通量密度不相关。这是因为我们的连续谱图追踪的是102 Au尺度的光盘，而不是103-4 Au尺度的致密气体。
A dense gas survey was carried out toward 10 low-mass embedded young sources in Taurus with the Nobeyama Millimeter Array (NMA) to investigate protostellar evolution. All the sources were observed in the H13CO+(J = 1-0) line, a high-density tracer. Significant H13CO+ emission (≥4.5 σ) was detected toward six of them. The H13CO+ emission is distributed roughly perpendicular to the molecular outflow axes, indicating that the H13CO+ line traces the dense envelopes associated with the central stars. The sizes and masses of the dense envelopes are estimated to be (1-7) × 103 AU and 0.01-0.2 M☉, respectively. The 10 sources are divided into the following three classes based on their H13CO+ intensities of the NMA maps, and their properties are studied using our own and other available data. Class A sources have H13CO+ emission centered on the star with its elongation perpendicular to the molecular outflow axes. These sources also have dense outflowing gas and centrally condensed parent cores. Class B sources have H13CO+ emission near the source positions and dense outflowing gas. The parent cores around class B sources, however, have a shallower density profile. Class C sources have neither H13CO+ emission nor wing emission in dense gas tracers. From these properties, we conclude that low-mass protostars evolve from class A, B to C sources by dissipating their parent cloud cores, which is consistent with the widely accepted ideas of star formation. In addition, these observational data suggest that significant dispersion of a parent core by a molecular outflow and main accretion phase ends at the early protostellar phase. Six of the 10 sources are detected in continuum emission at 87 GHz. The intensities of the H13CO+ emission do not correlate with the flux densities at 87 GHz. This is because our continuum maps trace compact disks on a 102 AU scale and not dense gas on a 103-4 AU scale.
T. Nakamoto：《恒星形成1999》野边山射电天文台。
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