MOLECULAR LINE OBSERVATIONS OF MCLD 123.5+24.9 IN THE POLARIS CIRRUS
MOLECULAR LINE OBSERVATIONS OF MCLD 123.5+24.9 IN THE POLARIS CIRRUS
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DOI：
10.1088/0004-637x/745/2/195
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发表时间：
2012-01
期刊：
影响因子：
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通讯作者：
T. Shimoikura;K. Dobashi;T. Sakurai;S. Takano;S. Nishiura;T. Hirota
中科院分区：
文献类型：
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作者：
T. Shimoikura;K. Dobashi;T. Sakurai;S. Takano;S. Nishiura;T. Hirota
本文介绍了利用野边山射电天文台45米望远镜对北极卷云MCLD123.5 +24.9方向的各种分子谱线进行毫米波观测的结果。MCLD 123.5+24.9是在弥漫卷云中形成的罕见致密核之一，在那里星星的形成可能很少发生。为了研究MCLD 123.5+24.9的结构、动力学和演化阶段，我们在来自13种不同分子的17条发射线中观察到了这个核心。CS、CCS和HC 3 N的发射线在整个堆芯都被强烈检测到，而SO和N2 H+的发射线很弱或未被检测到，表明MCLD 123.5+24.9在化学组成方面处于堆芯演化的早期阶段。根据CCS和HC_3 N的丰度分数，这被认为是化学年龄的指标，与其他核心的星星形成和不形成以及与文献中的模型计算的比较，我们认为，MCLD 123.5+24.9是在一个阶段之前，星星形成。从获得的C18 O数据，我们推导出MCLD 123.5+24.9的总分子量为150 pc的假定距离为123.5+24.9。MCLD 123.5+24.9中有三个子核心，分别称为CS-A、CS-B和CS-C。我们推导出它们的质量为0.2-0.6 M。我们还研究了MCLD 123.5+24.9和子核的动力学稳定性，通过应用维里定理，发现MCLD 123.5+24.9作为一个整体是不受引力约束的，而单个子核处于维里平衡，并且可以崩溃与施加在它们表面上的外部压力的小幅增加。
In this paper, we present results of millimeter-wave observations with various molecular lines made toward MCLD 123.5+24.9 in the Polaris cirrus using the 45 m telescope at Nobeyama Radio Observatory. MCLD 123.5+24.9 is one of the rare dense cores forming in diffuse cirrus clouds where star formation may rarely take place. In order to investigate the structure, dynamics, the evolutionary stage of MCLD 123.5+24.9, we observed this core in 17 emission lines from 13 different molecular species. Emission lines of CS, CCS, and HC3N are strongly detected all over the core, while those of SO and N2H+ are weak or remain undetected, indicating that MCLD 123.5+24.9 is in an early stage of core evolution in terms of chemical composition. Based on comparison of the fractional abundances of CCS and HC3N, which are considered indicators of chemical age, with those of other cores with and without star formation as well as with model calculations in the literature, we suggest that MCLD 123.5+24.9 is in a phase prior to star formation. From the C18O data obtained, we derived the total molecular mass of MCLD 123.5+24.9 to be ∼3 M☉ at an assumed distance of 150 pc. There are three subcores in MCLD 123.5+24.9, called CS-A, CS-B, and CS-C. We derived their masses to be 0.2–0.6 M☉. We also investigated the dynamical stability of MCLD 123.5+24.9 and the subcores by applying the virial theorem to find that MCLD 123.5+24.9 is not gravitationally bound as a whole, while the individual subcores are in the virial equilibrium and can collapse with a small increase of external pressure imposed on their surfaces.