Chemistry in disks
Chemistry in disks
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DOI：
10.1051/0004-6361/201832980
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发表时间：
2018-06
影响因子：
6.5
通讯作者：
S. Guilloteau;A. Dutrey;V.Wakelam;F.Hersant;D. Semenov;E. Chapillon;T.Henning;V. Bordeaux;Lab;Umr 5804;F-33270;Floirac;F. Cnrs;F. M. F. Astronomie-F.-M.-F.-Astronomie-103137464;Heidelberg;G. O. Astronomy;Astrophysics;Taipei;Taiwan;Robina Iram;S. d’Hères;France.
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文献类型：
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作者：
S. Guilloteau;A. Dutrey;V.Wakelam;F.Hersant;D. Semenov;E. Chapillon;T.Henning;V. Bordeaux;Lab;Umr 5804;F-33270;Floirac;F. Cnrs;F. M. F. Astronomie-F.-M.-F.-Astronomie-103137464;Heidelberg;G. O. Astronomy;Astrophysics;Taipei;Taiwan;Robina Iram;S. d’Hères;France.
上下文在星际介质和彗星中观察到几种含硫分子，与迄今为止只检测到CS，H2 CS和SO的原行星盘形成强烈对比。目标。我们结合联合收割机的观测和化学模型，以限制硫的丰度和它们的敏感性，在DM头原行星盘的物理和化学条件。方法.我们在CS、SO、SO2、OCS、CCS、H2 CS和H2S谱线上获得了4和6波段DM Tau的0.5“”阿塔卡玛大型毫米波阵列观测，达到了~5 mJy的灵敏度。使用非局部热力学平衡辐射传输程序RADEX和正演模拟工具ERFit，导出了其他物种的圆盘平均CS柱密度和上限。结果仅检测到CS，导出的柱密度约为2−6 × 1012 cm−2。我们报告的第一个初步检测的SO2在DM头。其他含硫物种的上限介于~1011和1014 cm−2之间。与这些值相匹配的最佳化学模型要求在r = 50−100 Au时气相C/O比为1.1。与化学建模，我们表明，含硫物种可以是强大的示踪剂的气相C/O比，表面反应速率，晶粒尺寸和紫外强度。结论.在DM Tau中没有检测到CS以外的各种含硫分子，这意味着气相中缺乏活性硫，要么是通过有效的冻结，要么是因为大多数元素硫都存在于其他大物种中，如彗星中所发现的。推断出的高CS/SO和CS/SO2比需要非太阳能的C/O气相比为100.1，这与最近在DM Tau中观察到的烃环一致。与CS相比，含氧S-物质的更强消耗可能与DM Tau中气态水的低观测丰度有关，并指出从气体中去除氧的机制。
Context. Several sulfur-bearing molecules are observed in the interstellar medium and in comets, in strong contrast to protoplanetary disks where only CS, H2CS, and SO have been detected so far. Aims. We combine observations and chemical models to constrain the sulfur abundances and their sensitivity to physical and chemical conditions in the DM Tau protoplanetary disk. Methods. We obtained 0.5′′ Atacama Large Millimeter Array observations of DM Tau in Bands 4 and 6 in lines of CS, SO, SO2, OCS, CCS, H2CS, and H2S, achieving a ~5 mJy sensitivity. Using the non-Local Thermodynamical Equilibrium radiative transfer code RADEX and the forward-modeling tool DiskFit, disk-averaged CS column densities and upper limits for the other species were derived. Results. Only CS was detected with a derived column density of ~2−6 × 1012 cm−2. We report a first tentative detection of SO2 in DM Tau. The upper limits range between ~1011 and 1014 cm−2 for the other S-bearing species. The best-fit chemical model matching these values requires a gas-phase C/O ratio of ≳1 at r ≳ 50−100 au. With chemical modeling we demonstrate that sulfur-bearing species could be robust tracers of the gas-phase C/O ratio, surface reaction rates, grain size and UV intensities. Conclusions. The lack of detections of a variety of sulfur-bearing molecules in DM Tau other than CS implies a dearth of reactive sulfur in the gas phase, either through efficient freeze-out or because most of the elemental sulfur is in other large species, as found in comets. The inferred high CS/SO and CS/SO2 ratios require a non-solar C/O gas-phase ratio of ≳1, consistent with the recent observations of hydrocarbon rings in DM Tau. The stronger depletion of oxygen-bearing S-species compared to CS is likely linked to the low observed abundances of gaseous water in DM Tau and points to a removal mechanism of oxygen from the gas.