arXiv 1604.050282016-04-18astro-ph.EP

金牛座X中的化学：金牛座原行星的分子含量

Chemistry in Disks X: The Molecular Content of Proto-planetary Disks in Taurus

S. Guilloteau, L. Reboussin, A. Dutrey, E. Chapillon, V. Wakelam, V. Piétu, E. Di Folco, D. Semenov, Th. Henning

备注：: To appear in Astronomy & Astrophysics
DOI：: 10.1051/0004-6361/201527088

摘要：

我们使用IRAM 30-m对金牛座御夫座区域的30个原行星盘进行了灵敏的宽带调查。我们同时观察到HCO $^+$（3-2）、HCN（3-2）、C $_2$ H（3-2）、CS（5-4）和SO的两个跃迁。我们将这些结果与以前的观测结果结合起来，以前的观测结果观察到$^{13}$ CO（2-1），CN（2-1），两条o-H $_2$ CO线和一条SO线。我们使用现有的干涉测量数据来获得CN和C $_2$ H在几个来源的激发温度。我们确定的特征尺寸的气体磁盘和柱密度的所有分子使用参数的幂律盘模型。我们的研究主要是对来自恒星的200-400 au的分子敏感。我们比较衍生的列密度的预测广泛的气体颗粒化学磁盘模型，在代表金牛座T磁盘的条件下。本研究提供了20例椎间盘中HCO $^+$的新检测，18例HCN，11例C $_2$ H，8例CS和4例SO。HCO $^+$在几乎所有的源中都被探测到，它的J=3-2线基本上是光学厚的，提供了对盘半径的良好估计。其他过渡是（至少部分地）光学薄的。柱密度比的变化与恒星或盘的任何特定性质无关。Herbig Ae恒星周围的样品似乎比金牛T恒星周围的样品分子少，尽管样品仍然很小。SO只在（可能更年轻的）嵌入对象中发现，也许反映了S化学的演变，由于随着时间的推移而增加消耗。总之，分子柱密度，特别是CN/HCN和CN/C $_2$ H比，通过冷盘中的气体颗粒化学很好地再现。这项研究提供了一个简单的分子在半径$> 200-300$ au的磁盘普查。将其扩展到更小的磁盘，或寻找丰度较低或更复杂的分子，需要更敏感的设施，即NOEMA和ALMA。

英文摘要：

(abridged) We used the IRAM 30-m to perform a sensitive wideband survey of 30 protoplanetary disks in the Taurus Auriga region. We simultaneously observed HCO$^+$(3-2), HCN(3-2), C$_2$H(3-2), CS(5-4), and two transitions of SO. We combine the results with a previous survey which observed $^{13}$CO (2-1), CN(2-1), two o-H$_2$CO lines and one of SO. We use available interferometric data to derive excitation temperatures of CN and C$_2$H in several sources. We determine characteristic sizes of the gas disks and column densities of all molecules using a parametric power-law disk model. Our study is mostly sensitive to molecules at 200-400 au from the stars. We compare the derived column densities to the predictions of an extensive gas-grain chemical disk model, under conditions representative of T Tauri disks. This survey provides 20 new detections of HCO$^+$ in disks, 18 in HCN, 11 in C$_2$H, 8 in CS and 4 in SO. HCO$^+$ is detected in almost all sources, and its J=3-2 line is essentially optically thick, providing good estimates of the disk radii. The other transitions are (at least partially) optically thin. Variations of the column density ratios do not correlate with any specific property of the star or disk. Disks around Herbig Ae stars appear less rich in molecules than those around T Tauri stars, although the sample remains small. SO is only found in the (presumably younger) embedded objects, perhaps reflecting an evolution of the S chemistry due to increasing depletion with time. Overall, the molecular column densities, and in particular the CN/HCN and CN/C$_2$H ratios, are well reproduced by gas-grain chemistry in cold disks. This study provides a census of simple molecules in disks of radii $> 200-300$ au. Extending that to smaller disks, or searching for less abundant or more complex molecules requires a much more sensitive facility, i.e. NOEMA and ALMA.

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