Extended emission of D 2 H + in a prestellar core
Extended emission of D 2 H + in a prestellar core
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星前核心中 D 2 H 的延长发射
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
K. Menten
中科院分区：
文献类型：
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作者：
B. Parise;A. Belloche;F. Du;R. Güsten;K. Menten
上下文在过去的几年里，H2 D+和D2 H+分子作为冷的和贫化的致密分子云核的探针而受到关注。这些离子是分子氘分馏的基础，这是在恒星形成区域观察到的一个共同特征。H2 D+现在被常规地观察到，但是寻找其同位素体D2 H+仍然是困难的，因为其基帕拉跃迁的频率很高（692 GHz）。目标。我们观察到的H2 D+和D2 H+的分子跃迁在一个寒冷的星前核心的特点的氘化学的根源。方法.由于APEX望远镜上灵敏的多像素CHAMP +接收器满足了所需的优良天气条件，我们不仅成功地探测到位于L1688云中的H-MM 1星前核中的D2 H+，而且还获得了有关其发射空间范围的信息。我们还在同一来源中检测到372 GHz的H2 D+。我们分析这些检测使用非LTE辐射传输代码和国家的最先进的自旋相关的化学模型。结果这是首次在太空中安全探测到D2 H+。此外，发射在CHAMP +阵列的几个像素上延伸，即在至少40 μ m的尺度上，对应于104800 Au。在LTE近似下，根据假设的温度，我们推导出两种分子的柱密度为10 12 - 10 13 cm −2，而在非LTE分析的基础上，柱密度高出两个数量级。结论.我们的模型表明，在核心中心的CO消耗水平必须非常高（>10，甚至>100，如果核心的温度是10 K左右），矛盾的CO消耗水平直接测量在其他核心。观察H2 D+的空间分布和直接测量的CO消耗在H-MM 1将是必不可少的，以确认是否需要修改目前的化学模型调查的基础上氘分馏的分子。
Context. In the past years, the H2D + and D2H + molecules have gained attention as probes of cold and depleted dense molecular cloud cores. These ions are the basis of molecular deuterium fractionation, a common characteristic observed in star-forming regions. H2D + is now routinely observed, but the search for its isotopologue D2H + is still difficult because of the high frequency of its ground para transition (692 GHz). Aims. We observed molecular transitions of H2D + and D2H + in a cold prestellar core to characterize the roots of deuterium chemistry. Methods. Thanks to the sensitive multi-pixel CHAMP + receiver on the APEX telescope where the required excellent weather conditions are met, we not only successfully detect D2H + in the H-MM1 prestellar core located in the L1688 cloud, but also obtain information on the spatial extent of its emission. We also detect H2D + at 372 GHz in the same source. We analyze these detections using a non-LTE radiative transfer code and a state-of-the-art spin-dependent chemical model. Results. This observation is the first secure detection of D2H + in space. The emission is moreover extended over several pixels of the CHAMP + array, i.e. on a scale of at least 40 �� , corresponding to ∼4800 AU. We derive column densities on the order of 10 12 –10 13 cm −2 for both molecules in the LTE approximation depending on the assumed temperature, and up to two orders of magnitude higher based on a non-LTE analysis. Conclusions. Our modeling suggests that the level of CO depletion must be extremely high (>10, and even >100 if the temperature of the core is around 10 K) at the core center, contradicting CO depletion levels directly measured in other cores. Observation of the H2D + spatial distribution and direct measurement of the CO depletion in H-MM1 will be essential to confirm whether present chemical models investigating the basis of deuterium fractionation of molecules need to be revised.