Hot corinos in NGC 1333-IRAS4B and IRAS2A
Hot corinos in NGC 1333-IRAS4B and IRAS2A
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DOI：
10.1051/0004-6361:20065139
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发表时间：
2007-02-01
影响因子：
6.5
通讯作者：
Lefloch, B.
中科院分区：
文献类型：
--
作者：
Bottinelli, S.;Ceccarelli, C.;Lefloch, B.
上下文复杂的有机分子已经在巨大的热核心中被发现了二十多年，直到最近才在三个热的科里诺（围绕太阳的原恒星的内部区域，尘埃温度超过100 K）中被发现。由于热的Corino具有类似于100 Au的大小（即，太阳系范围的数量级），它是特别相关的，以了解它们是否是常见的，并确定复杂的有机分子的形成途径（S）。关于这个主题还有很多东西要学，因为即使是最近的模型也预测在低质量的原恒星中不可能形成这些分子。我们的目标是扩大已知的热corino的数量，并进行第一次比较研究与热核心。最终的目标是了解复杂的有机分子是在气相中还是在颗粒表面形成，以及可能的关键参数是什么。我们用IRAM-30 m观测了低质量原恒星样品中HCOOH、HCOOCH 3 CH 3 OCH 3 CH 3CN和C2 H5 CN的毫米级转动跃迁。利用转动图方法，结合源的结构信息，计算了观测分子的丰度。为了解释这些丰度，我们回顾了上述分子的形成过程。我们报告了对NGC 1333-IRAS 4 B和NGC 1333-IRAS 2A的HCOOCH 3和/或CH 3CN的检测。我们发现，在热corinos的O-轴承分子的丰度比甲醇或甲醛是可比的，约统一，并相对（取决于如何确定的比例）高于那些在热的核心和银河系中心云。到目前为止，复杂的有机分子在所有寻找它们的热corino中都被检测到，这表明它是低质量原恒星的共同阶段。虽然一些证据表明，这些分子（特别是HCOOH和HCOOCH 3）的颗粒表面合成（无论是在冷或暖相），目前的数据不允许我们忽视气相形成。需要更多的观测，实验室和理论研究，以提高我们对热corino的理解。
Context. Complex organic molecules have been detected in massive hot cores for over two decades, and only recently in three hot corinos (the inner regions surrounding Sun-like protostars, where the dust temperature exceeds 100 K). Since hot corinos have sizes of similar to 100 AU (i.e., of the order of the extent of the Solar System), it is particularly relevant to understand whether they are common and to identify the formation route(s) of complex organic molecules. Much has yet to be learned on this topic, since even recent models predicted it was not possible to form these molecules in low-mass protostars.Aims. We aim to enlarge the number of known hot corinos and carry out a first comparative study with hot cores. The ultimate goal is to understand whether complex organic molecules form in the gas phase or on grain surfaces, and what the possible key parameters are.Methods. We observed millimeter rotational transitions of HCOOH, HCOOCH3 CH3OCH3 CH3CN and C2H5CN in a sample of low-mass protostars with the IRAM-30 m. Using the rotational diagram method coupled with the information about the sources' structure, we calculate the abundances of the observed molecules. To interpret these abundances, we review the proposed formation processes of the above molecules.Results. We report the detection of HCOOCH3 and/or CH3CN towards NGC 1333-IRAS4B and NGC 1333-IRAS2A. We find that abundance ratios of O-bearing molecules to methanol or formaldehyde in hot corinos are comparable and about unity, and are relatively (depending on how the ratios are determined) higher than those in hot cores and in Galactic center clouds.Conclusions. So far, complex organic molecules were detected in all the hot corinos where they were searched for, suggesting that it is a common phase for low-mass protostars. While some evidence points to grain-surface synthesis (either in the cold or warm-up phase) of these molecules (in particular for HCOOH and HCOOCH3), the present data do not allow us to disregard gas-phase formation. More observational, laboratory, and theoretical studies are required to improve our understanding of hot corinos.