Molecular Line Observations of Carbon-Chain-Producing Regions L1495B and L1521B
Molecular Line Observations of Carbon-Chain-Producing Regions L1495B and L1521B
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DOI：
10.1086/425261
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发表时间：
2004-09
期刊：
影响因子：
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通讯作者：
T. Hirota;H. Maezawa;S. Yamamoto
中科院分区：
文献类型：
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作者：
T. Hirota;H. Maezawa;S. Yamamoto
我们首次全面研究了静止无星核L1495B和L1521B的物理和化学性质，这两个核已知含有丰富的碳链分子，如TMC-1和L1521E的氰聚yne峰。我们检测了CCS、C3S、C4H、HC3N、HC5N等多种碳链分子的无线电谱线。另一方面，NH3谱线较弱，未检测到N2H+谱线。根据我们对HC3N、CCS和C3S线的测绘观测，L1495B和L1521B的致密核结构紧凑，半径分别为0.063和0.044 pc，具有简单的椭圆结构。CCS的分布似乎不同于那些被充分研究的无星核L1498和L1544，其中CCS的分布呈壳状结构。由于在L1495B和L1521B中检测到H13CO+， HN13C和C34S谱线，这些核心的密度足够高，可以激发NH3和N2H+谱线。因此，NH3和N2H+相对于碳链分子的丰度明显不足，如L1521E所见。我们发现，较长的碳链分子，如HC5N和C4H，在TMC-1中比在L1495B和L1521B中更丰富，而含硫分子，如C34S、CCS和C3S，在TMC-1中含量相当。L1495B和L1521B中观察到的分子分布和丰度与L1521E非常相似，强烈表明L1495B和L1521B处于非常早期的物理和化学演化阶段。
We present the first comprehensive study of physical and chemical properties of quiescent starless cores L1495B and L1521B, which are known to be rich in carbon-chain molecules like the cyanopolyyne peak of TMC-1 and L1521E. We have detected radio spectral lines of various carbon-chain molecules, such as CCS, C3S, C4H, HC3N, and HC5N. On the other hand, the NH3 lines are weak and the N2H+ lines are not detected. According to our mapping observations of the HC3N, CCS, and C3S lines, the dense cores in L1495B and L1521B are compact, with radius 0.063 and 0.044 pc, respectively, and have a simple elliptical structure. The distributions of CCS seem to be different from those of well-studied starless cores, L1498 and L1544, where the distribution of CCS shows a shell-like structure. Since the H13CO+, HN13C, and C34S lines are detected in L1495B and L1521B, the densities of these cores are high enough to excite the NH3 and N2H+ lines. Therefore, the abundances of NH3 and N2H+ relative to carbon-chain molecules are apparently deficient, as observed in L1521E. We found that longer carbon-chain molecules, such as HC5N and C4H, are more abundant in TMC-1 than in L1495B and L1521B, while those of sulfur-bearing molecules, such as C34S, CCS, and C3S, are comparable. Both distributions and abundances of the observed molecules in L1495B and L1521B are quite similar to those in L1521E, strongly suggesting that L1495B and L1521B are in a very early stage of physical and chemical evolution.