双DCO +环揭示了IM Lup周围外盘中的CO冰解吸
Double DCO+ rings reveal CO ice desorption in the outer disk around IM Lup
摘要：
在一个原行星盘中，热解吸和非热解吸过程的组合控制着挥发物从冰粒地幔释放到气相的位置。非热解吸应导致在盘区域中的挥发性富集气体，否则完全冻结。本文给出了年轻恒星IMLup周围1.4mm连续谱的ALMA观测结果，C18 O2 -1，H13 CO + 3-2和DCO+ 3-2的~0”.5分辨率的辐射.这些尘埃和气体示踪剂的图像清晰地分辨出来。DCO+谱线显示出一对引人注目的同心发射环，其峰值半径为~0”.6和2”（分别为~90和300 AU）。基于盘化学模型比较，内部DCO+环与由于盘温度径向降低而导致的CO冻结和热解吸的平衡相关联。外DCO+环的解释是在低柱密度外盘CO冰的非热解吸，重新填充磁盘中平面与冷CO气体。然后CO气体与丰富的H2 D+反应形成观察到的DCO+外环。这些观测结果表明，空间分辨的DCO+发射可用于追踪最外层盘区域中隐藏的冷气体储层，为它们的化学和运动学打开了一个新的窗口。
英文摘要：
In a protoplanetary disk, a combination of thermal and non-thermal desorption processes regulate where volatiles are liberated from icy grain mantles into the gas phase. Non-thermal desorption should result in volatile-enriched gas in disk-regions where complete freeze-out is otherwise expected. We present ALMA observations of the disk around the young star IM Lup in 1.4 mm continuum, C18O 2-1, H13CO+ 3-2 and DCO+ 3-2 emission at ~0".5 resolution. The images of these dust and gas tracers are clearly resolved. The DCO+ line exhibits a striking pair of concentric rings of emission that peak at radii of ~0".6 and 2" (~90 and 300 AU, respectively). Based on disk chemistry model comparison, the inner DCO+ ring is associated with the balance of CO freeze-out and thermal desorption due to a radial decrease in disk temperature. The outer DCO+ ring is explained by non-thermal desorption of CO ice in the low-column-density outer disk, repopulating the disk midplane with cold CO gas. The CO gas then reacts with abundant H2D+ to form the observed DCO+ outer ring. These observations demonstrate that spatially resolved DCO+ emission can be used to trace otherwise hidden cold gas reservoirs in the outmost disk regions, opening a new window onto their chemistry and kinematics.
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