原恒星中甲醛和甲醇的氘化：来自过去快高密度预坍缩阶段的扰动
Formaldehyde and methanol deuteration in protostars: fossiles from a past fast high density pre-collapse phase
摘要：
十年来，在低质量原恒星周围观察到了几种分子的极高氘化。其中，甲醛和甲醇呈现特别高的氘化，观察到丰富的二重和三重氘化形式。这两个物种被认为是主要形成在星际颗粒在低温和致密的预塌缩阶段由H和D原子添加在冰CO。我们在这里提出了一个理论研究的甲醛和甲醇氘代与我们的气体颗粒模型，GRAINOBLE。该模型考虑到地幔的多层性质，并探讨了对约束不良的化学和表面模型参数的不确定性的结果的鲁棒性。将模型预测值与观测值进行比较，可以得出两个主要结果：i）观测到的高氘量是在坍缩前阶段的最后阶段获得的，此时密度达到5 × 10^6 cm^-3，而且这个阶段非常快，只持续了几千年。ii）D和H的提取和取代反应在弥补所观察到的氘化率方面至关重要;这项工作显示了化学成分作为重建原恒星过去历史的工具的力量。
英文摘要：
Extremely high deuteration of several molecules have been observed around low mass protostars since a decade. Among them, formaldehyde and methanol present particularly high deuteration, with observations of abundant doubly and triply deuterated forms. Both species are thought to be mainly formed on interstellar grains during the low temperature and dense pre-collapse phase by H and D atom additions on the iced CO. We present here a theoretical study of the formaldehyde and methanol deuteration obtained with our gas-grain model, GRAINOBLE. This model takes into account the multilayer nature of the mantle and explores the robustness of the results against the uncertainties of poorly constrained chemical and surface model parameters. The comparison of the model predictions with the observations leads to two major results: i) the observed high deuteration is obtained during the last phase of the pre-collapse stage, when the density reaches 5 10^6 cm^-3, and this phase is fast, lasting only several thousands years. ii) D and H abstraction and substitution reactions are crucial in making up the observed deuteration ratios; This work shows the power of chemical composition as a tool to reconstruct the past history of protostars.
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