论文标题
观察星际冰中复杂有机分子形成的发作
Observations of the Onset of Complex Organic Molecule Formation in Interstellar Ices
论文作者
论文摘要
研究了分离的致密分子核，以研究星际冰中复杂有机分子形成的发作。用低质量恒星（B59，B335和L483）和一个无星核（L694-2）的持续形成三个核心，我们将视线采样至九个背景星和五个年轻的恒星物体（YSOS; a_k〜0.5-0.5-4.7）。这些星星的光谱从2-5 $ $ m的光谱与NASA的红外望远镜设施（IRTF）同时显示H $ _2 $ O（3.0 $ $ M）的核心，CH $ _3 $ _3 $ OH（C-H伸展模式，3.53 $ $ M）和CO（4.67 $ M）$ M M）iCes。 CO冰是由9颗星追溯到的，其中五个恒星由于CO与Polar Ice的混合物（CO $ _R $）的混合物（大概是Ch $ _3 $ oh）而显示出长波长翼。这些视线中的两条还显示了CH $ _3 $ OH的独立检测。对于这些，我们发现CH $ _3 $ OH：CO $ _R $的比率分别为0.55 $ \ pm $ 0.06和0.73 $ \ pm $ \ pm $ 0.07，分别从L483和L694-2。 CO和CH $ _3 $ OH的检测首次通过视线向背景恒星观察到了CO将CO转换为Ch $ _3 $ OH ICE的转换。沿着视线，大多数CO都存在于天然气阶段，$ \ leq $ 15％的CO被冻结了。但是，相对于CO（〜50％），CH $ _3 $ OH ICE很丰富，并且主要作为CH $ _3 $ oh-oh-rich Co Ice层。只有一小部分的视线包含ch $ _3 $ oh冰，大概是密度最高的。 CO转换为ch $ _3 $ oh可以解释在后期1类低质量YSO信封中发现的CH $ _3 $ OH ICE的丰度（CH $ _3 $ OH：CO $ _R $ 〜0.5-0.5-0.6）。对于高质量YSO和一类0 yso，该比率有很大的变化，暗示局部变化可能会影响冰的形成。大的CH $ _3 $ OH冰的丰度表明，在没有较高能量颗粒相互作用的情况下（例如宇宙射线），在恒星前阶段，复杂有机分子的形成很可能是在恒星前阶段的形成。
Isolated dense molecular cores are investigated to study the onset of complex organic molecule formation in interstellar ice. Sampling three cores with ongoing formation of low-mass stars (B59, B335, and L483) and one starless core (L694-2) we sample lines of sight to nine background stars and five young stellar objects (YSOs; A_K ~0.5 - 4.7). Spectra of these stars from 2-5 $μ$m with NASA's Infrared Telescope Facility (IRTF) simultaneously display signatures from the cores of H$_2$O (3.0 $μ$m), CH$_3$OH (C-H stretching mode, 3.53 $μ$m) and CO (4.67 $μ$m) ices. The CO ice is traced by nine stars in which five show a long wavelength wing due to a mixture of CO with polar ice (CO$_r$), presumably CH$_3$OH. Two of these sight lines also show independent detections of CH$_3$OH. For these we find the ratio of the CH$_3$OH:CO$_r$ is 0.55$\pm$0.06 and 0.73$\pm$0.07 from L483 and L694-2, respectively. The detections of both CO and CH$_3$OH for the first time through lines of sight toward background stars observationally constrains the conversion of CO into CH$_3$OH ice. Along the lines of sight most of the CO exists in the gas phase and $\leq$15% of the CO is frozen out. However, CH$_3$OH ice is abundant with respect to CO (~50%) and exists mainly as a CH$_3$OH-rich CO ice layer. Only a small fraction of the lines of sight contains CH$_3$OH ice, presumably that with the highest density. The high conversion of CO to CH$_3$OH can explain the abundances of CH$_3$OH ice found in later stage Class 1 low mass YSO envelopes (CH$_3$OH:CO$_r$ ~ 0.5-0.6). For high mass YSOs and one Class 0 YSO this ratio varies significantly implying local variations can affect the ice formation. The large CH$_3$OH ice abundance indicates that the formation of complex organic molecules is likely during the pre-stellar phase in cold environments without higher energy particle interactions (e.g. cosmic rays).
