Deuteration around the ultracompact HII region Monoceros R2-猫眼课题宝

DOI：

10.1051/0004-6361/201423407

发表时间：

2014-06

期刊：

Astronomy and Astrophysics

影响因子：

6.5

通讯作者：

中科院分区：

物理与天体物理2区

文献类型：

作者：

S. Treviño-Morales;P. Pilleri;A. Fuente;C. Kramer;È. Roueff;M. Gonz'alez-Garc'ia;J. Cernicharo;M. Gerin;J. Goicoechea;J. Pety;O. Bern'e;V. Ossenkopf;D. Ginard;S. Garc'ia-Burillo;J. Rizzo;S. Viti

上下文大质量恒星形成区域Monoceros R2（Mon R2）拥有最近的超紧凑Hii区域，其中电离和分子气体之间的光子主导区域（PDR）可以用目前的单碟望远镜进行空间解析。目标。我们的目的是研究氘代分子对Mon R2的化学，以确定氘馏分周围的highUV照射PDR和调查这些物种的化学。方法.我们使用的IRAM-30米望远镜进行了公正的光谱调查对两个重要的位置（即IF和MP2）在周一R2在1，2和3毫米。这光谱调查是我们的研究在这个巨大的恒星形成区域的氘的观测基础。我们的高光谱分辨率观测（0.25-0.65 km s-1）使我们能够解析所探测到的不同物种的谱线轮廓。结果我们发现在Mon R2的两个位置处的氘代物种的丰富化学，检测到C2 D、DCN、DNC、DCO +、D2CO、HDCO、NH 2D和N2 D+以及它们相应的氢化物种和更稀有的同位素。我们观测的高光谱分辨率使我们能够分辨出三个速度分量：10 km s −1的分量在两个位置都被探测到，似乎与暴露于IRS 1紫外辐射最多的层有关; 12 km s −1的分量被发现朝向IF位置，似乎与前景分子气体有关;最后，8.5 km s-1的分量只在MP2位置被探测到，很可能与低紫外辐射的PDR有关。我们导出了氘代物质（连同它们的氢化对应物）的柱密度，并将氘分数确定为Dfrac = [XD]/[XH]。对于所有观察到的物质，Dfrac的值都在0.01左右，除了HCO +和N2 H+，它们的值低10倍。在Mon R2中发现的值与在Orion Bar中测得的值相似，并且可以用伪时间依赖性气相模型很好地解释，其中氘代主要通过与H2 D+，CH 2D +和C2 HD+的离子-分子反应发生。最后，[H 13 CN]/[HN 13 C]的比值在10 km s −1的分量中非常高（10.11），这也与我们的模型预测的年龄在100万年到几百万年之间一致。结论.氘化学是研究低质量和高质量恒星形成区的良好工具。然而，虽然低质量恒星形成区似乎很好地表征了Dfrac（N2 H+）或rDfrac（HCO +），但需要更完整的化学建模来确定大质量恒星形成区的日期。这是由于更高的气体温度以及大质量原恒星的快速演化。

Context. The massive star-forming region Monoceros R2 (Mon R2) hosts the closest ultra-compact Hii region, where the photondominated region (PDR) between the ionized and molecular gas can be spatially resolved with current single-dish telescopes. Aims. We aim at studying the chemistry of deuterated molecules toward Mon R2 to determine the deuterium fractions around a highUV irradiated PDR and investigate the chemistry of these species. Methods. We used the IRAM-30 m telescope to carry out an unbiased spectral survey toward two important positions (namely IF and MP2) in Mon R2 at 1, 2, and 3 mm. This spectral survey is the observational basis of our study of the deuteration in this massive starforming region. Our high spectral resolution observations (∼0.25–0.65 km s −1 ) allowed us to resolve the line profiles of the different species detected. Results. We found a rich chemistry of deuterated species at both positions of Mon R2, with detections of C2D, DCN, DNC, DCO + , D2CO, HDCO, NH2D, and N2D + and their corresponding hydrogenated species and rarer isotopologs. The high spectral resolution of our observations allowed us to resolve three velocity components: the component at 10 km s −1 is detected at both positions and seems associated with the layer most exposed to the UV radiation from IRS 1; the component at 12 km s −1 is found toward the IF position and seems related to the foreground molecular gas; finally, a component at 8.5 km s −1 is only detected toward the MP2 position, most likely related to a low-UV irradiated PDR. We derived the column density of the deuterated species (together with their hydrogenated counterparts), and determined the deuterium fractions as Dfrac = [XD]/[XH]. The values of Dfrac are around 0.01 for all the observed species, except for HCO + and N2H + , which have values 10 times lower. The values found in Mon R2 are similar to those measured in the Orion Bar, and are well explained with a pseudo-time-dependent gas-phase model in which deuteration occurs mainly via ion-molecule reactions with H2D + ,C H 2D + and C2HD + . Finally, the [H 13 CN]/[HN 13 C] ratio is very high (∼11) for the 10 km s −1 component, which also agree with our model predictions for an age of ∼0.01 to a few 0.1 Myr. Conclusions. The deuterium chemistry is a good tool for studying the low-mass and high-mass star-forming regions. However, while low-mass star-forming regions seem well characterized with Dfrac(N2H + )o rDfrac(HCO + ), a more complete chemical modeling is required to date massive star-forming regions. This is due to the higher gas temperature together with the rapid evolution of massive protostars.

Deuteration around the ultracompact HII region Monoceros R2

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