Orion Bar中的氘化学PDR -CH2D +主演的“温暖”化学
Deuterium chemistry in the Orion Bar PDR - "warm" chemistry starring CH2D+
摘要：
气态分子中高水平的氘分馏通常与寒冷区域有关，例如星前核。在热的环境中也观察到显著的分馏比，例如热的核心或热的科里诺斯，在那里它们被认为是由围绕尘埃颗粒的冰冷地幔蒸发产生的，因此是先前冷（气相或颗粒表面）化学的残余物。最近在70 K的特征温度下对猎户座棒的DCN的检测表明，在PDR中也可以检测到高氘分馏。因此猎户座棒团似乎是一个很好的环境，用于观察研究微温气体中的氘分馏，允许在不同的温度范围内验证化学模型，其中主要的分馏过程被预测为不同于冷气体（<20 K）。我们的目标是详细研究猎户座酒吧PDR中工作的化学观察，以了解DCN是否是由冰幔蒸发产生的，或者是温暖的气相化学的结果，涉及CH 2D+前体离子（比通常的H2 D+前体更高的温度）。使用APEX和IRAM 30米望远镜，我们将选定的氘代物种瞄准猎户座酒吧的两个团块。我们证实了DCN的检测，并检测到两个新的氘代分子（DCO+和HDCO）在猎户座酒吧PDR的一个团块。发现HCN和H2 CO中存在显着的氘分馏，但HCO+中的分馏较低。我们还给出了与氘化学相关的其他分子的上限。(...)我们证明了CH 2D+驱动的热氘化学在团块中起作用的证据。
英文摘要：
High levels of deuterium fractionation in gas-phase molecules are usually associated with cold regions, such as prestellar cores. Significant fractionation ratios are also observed in hot environments such as hot cores or hot corinos, where they are believed to be produced by the evaporation of the icy mantles surrounding dust grains, and thus are remnants of a previous cold (either gas-phase or grain surface) chemistry. The recent detection of DCN towards the Orion Bar, in a clump at a characteristic temperature of 70K, has shown that high deuterium fractionation can also be detected in PDRs. The Orion Bar clumps thus appear as a good environment for the observational study of deuterium fractionation in luke-warm gas, allowing to validate chemistry models in a different temperature range, where dominating fractionation processes are predicted to be different than in cold gas (< 20K). We aimed at studying observationally in detail the chemistry at work in the Orion Bar PDR, to understand if DCN is produced by ice mantle evaporation, or is the result of warm gas-phase chemistry, involving the CH2D+ precursor ion (which survives higher temperatures than the usual H2D+ precursor). Using the APEX and the IRAM 30m telescopes, we targetted selected deuterated species towards two clumps in the Orion Bar. We confirmed the detection of DCN and detected two new deuterated molecules (DCO+ and HDCO) towards one clump in the Orion Bar PDR. Significant deuterium fractionations are found for HCN and H2CO, but a low fractionation in HCO+. We also give upper limits for other molecules relevant for the deuterium chemistry. (...) We show evidence that warm deuterium chemistry driven by CH2D+ is at work in the clumps.
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