Abundant Carbon-Chain Molecules toward the Low-Mass Protostar IRAS 04368+2557 in L1527
Abundant Carbon-Chain Molecules toward the Low-Mass Protostar IRAS 04368+2557 in L1527
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DOI：
10.1086/523635
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
N. Sakai;T. Sakai;T. Hirota;S. Yamamoto
中科院分区：
文献类型：
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作者：
N. Sakai;T. Sakai;T. Hirota;S. Yamamoto
我们在低质量恒星形成区L1527探测到了C_4H_2（J = 100，10 - 90，9），C_4H（N = 9-8，F_1，F_2），l-C_3 H_2（41，3 - 31，2）和CH_3CCH（J = 5-4，K = 2）等碳链分子的高激发线。特别地，C4 H的F1线与1.7K（TMB）一样强。C_4H_2的转动温度为12.3 ± 0.8K，高于TMC-1的转动温度（3.8K）。此外，C4 H2的柱密度约为TMC-1的1/4，表明L1527中的碳链分子丰富，是一个恒星形成区。小测绘观测表明，C4 H，C4 H2，和c-C3 H2的排放分布从降落包线的内部。此外，我们还在20 GHz区域探测到了C5 H、HC 7 N和HC 9 N的谱线。由于碳链分子通常缺乏恒星形成的核心，上述结果不能简单地用现有的化学模型来解释。提出以下假设。如果L1527星前坍缩的时间尺度比其他恒星形成核心的时间尺度短，那么碳链分子就可以在核心的中心部分存活下来。此外，由于星星形成活动而产生的碳链分子的再生过程也将发挥重要作用。甲烷从谷壳的蒸发将驱动再生过程。目前的观测结果显示，在原恒星附近的温暖和密集的区域中存在新的化学物质，称为“温暖碳链化学”（WCCC）。
We have detected the high-excitation lines of carbon-chain molecules such as C4H2 (J = 100,10–90,9), C4H (N = 9–8, F1, F2), l-C3H2 (41,3-31,2), and CH3CCH (J = 5–4, K = 2) toward a low-mass star-forming region, L1527. In particular, the F1 line of C4H is as strong as 1.7 K (TMB). The rotational temperature of C4H2 is determined to be 12.3 ± 0.8 K, which is higher than that in TMC-1 (3.8 K). Furthermore, the column density of C4H2 is derived to be about 1/4 of that in TMC-1, indicating that carbon-chain molecules are abundant in L1527 for a star-forming region. Small mapping observations show that the C4H, C4H2, and c-C3H2 emissions are distributed from the infalling envelope to the inner part. Furthermore, we have detected the lines of C5H, HC7N, and HC9N in the 20 GHz region. Since the carbon-chain molecules are generally deficient in star-forming cores, the above results cannot simply be explained by the existing chemical models. The following hypothesis is proposed. If the timescale of the prestellar collapse in L1527 were shorter than those of the other star-forming cores, the carbon-chain molecules could survive in the central part of the core. In addition, regeneration processes of the carbon-chain molecules due to star formation activities would play an important role. Evaporation of CH4 from the grain mantles would drive the regeneration processes. The present observations show new chemistry in a warm and dense region near the protostars, which is named “warm carbon-chain chemistry (WCCC).”