Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars
Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars
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DOI：
10.1051/0004-6361:200400026
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发表时间：
2004-06
影响因子：
6.5
通讯作者：
Wing-Fai Thi Gerd-Jan van Zadelhoff;E. F. V. D. L. Observatory;nl;U. Amsterdam;D. Physics;Astronomy;University College London;UK.;K. Instituut
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文献类型：
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作者：
Wing-Fai Thi Gerd-Jan van Zadelhoff;E. F. V. D. L. Observatory;nl;U. Amsterdam;D. Physics;Astronomy;University College London;UK.;K. Instituut
本文报道了对两颗金牛座T星（LkCa 15和TW Hya）和两颗赫比格Ae星（HD 163296和MWC 480）周围原行星盘中选定分子的低J和高J跃迁的单碟观测结果。检测到简单分子，如CO、13 CO、HCO +、CN和HCN。在金牛座T星星LkCa 15附近发现了几条H2 CO谱线，但在其他天体中没有发现。没有检测到CH 3OH，相对于H2的丰度为10 −9 − 10 −8。SO和CS线已被搜索，而没有搜索。谱线比表明，分子发射来自中平面和上层之间的盘状大气的稠密（10 6 - 10 8 cm −3）和适度温暖（T = 20-40 K）的中间高度区域，与盘状大气化学模型的预测一致。磁盘的大小估计从模型拟合到12个CO 3-2线配置文件。大多数物种的丰度低于太阳质量原恒星IRAS 16293-2422周围的包层。冷中面的冻结和上层恒星和星际紫外光子的光解可能是耗尽的原因。CN在所有的圆盘中都被强烈地探测到，并且CN/HCN的丰度比在Herbig Ae恒星中甚至比在银河系光子占主导地位的区域中发现的更高，证明了来自上层中心物体的辐射的光解的重要性。DCO +在TW Hya方向被检测到，但在其他物体中没有。推知的DCO + /HCO +比值高达1.035，这与盘中氘分馏的模型一致，其中包括CO的强烈耗尽。从HCO +推知的中间高度区域的电离分数至少为10 −11 − 10 −10，与最近H2 D+观测中得出的中平面电离分数相当。相比
The results of single-dish observations of low- and high-J transitions of selected molecules from pro- toplanetary disks around two T Tauri stars (LkCa 15 and TW Hya) and two Herbig Ae stars (HD 163296 and MWC 480) are reported. Simple molecules such as CO, 13 CO, HCO + , CN and HCN are detected. Several lines of H2CO are found toward the T Tauri star LkCa 15 but not in other objects. No CH3OH has been detected down to abundances of 10 −9 − 10 −8 with respect to H2. SO and CS lines have been searched for without suc- cess. Line ratios indicate that the molecular emission arises from dense (10 6 -10 8 cm −3 ) and moderately warm (T ∼ 20-40 K) intermediate height regions of the disk atmosphere between the midplane and the upper layer, in accordance with predictions from models of the chemistry in disks. The sizes of the disks were estimated from model fits to the 12 CO 3-2 line profiles. The abundances of most species are lower than in the envelope around the solar-mass protostar IRAS 16293-2422. Freeze-out in the cold midplane and photodissociation by stellar and interstellar ultraviolet photons in the upper layers are likely causes of the depletion. CN is strongly detected in all disks, and the CN/HCN abundance ratio toward the Herbig Ae stars is even higher than that found in galactic photon-dominated regions, testifying to the importance of photodissociation by radiation from the central object in the upper layers. DCO + is detected toward TW Hya, but not in other objects. The high inferred DCO + /HCO + ratio of ∼0.035 is consistent with models of the deuterium fractionation in disks which include strong depletion of CO. The inferred ionization fraction in the intermediate height regions as deduced from HCO + is at least 10 −11 − 10 −10 , comparable to that derived for the midplane from recent H2D + observations. Comparison with