TW Hya Rosetta Stone项目I：DCN和DCO +的径向和垂直分布
The TW Hya Rosetta Stone Project I: Radial and vertical distributions of DCN and DCO+
摘要：
分子的D/H比值常被用来探测太阳系挥发物的化学历史。然而，目前还不清楚太阳星云的哪些部分拥有活跃的氘分馏化学。为了解决这个问题，我们提出了0”.2-0”.4 ALMA观测DCO+和DCN 2-1，3-2和4-3对TW Hya附近的原行星盘，作为TW Hya Rosetta Stone项目的一部分，增加了档案数据。DCO+的特点是在70金半径卵石盘的激发温度为~40 K，表明从温暖的，升高的分子层发射。然而，DCN存在于甚至更高的温度下。DCO+和DCN都在内盘中呈现大量的发射空腔，而在外盘中，DCO+和DCN形态发散：大多数DCN发射起源于峰值约30 μ m的窄环，一些额外的扩散DCN发射存在于较大的半径处，而DCO+存在于延伸超过卵石盘的宽结构环中。基于参数磁盘丰度模型，这些发射模式可以解释为一个接近恒定的DCN丰度外腔，并增加DCO+丰度与半径。似乎有一个活跃的氘分馏化学在TW Hya周围的多个磁盘区域，但不是在冷的星子形成的中平面和内部磁盘。需要更多的观测来探索在后面这些区域中是否真的不存在氘分馏，以及它的缺乏是否是一个共同的特征，或者是旧TW Hya盘特有的东西。
英文摘要：
Molecular D/H ratios are frequently used to probe the chemical past of Solar System volatiles. Yet it is unclear which parts of the Solar Nebula hosted an active deuterium fractionation chemistry. To address this question, we present 0".2-0".4 ALMA observations of DCO+ and DCN 2-1, 3-2 and 4-3 towards the nearby protoplanetary disk around TW Hya, taken as part of the TW Hya Rosetta Stone project, augmented with archival data. DCO+ is characterized by an excitation temperature of ~40 K across the 70 au radius pebble disk, indicative of emission from a warm, elevated molecular layer. Tentatively, DCN is present at even higher temperatures. Both DCO+ and DCN present substantial emission cavities in the inner disk, while in the outer disk the DCO+ and DCN morphologies diverge: most DCN emission originates from a narrow ring peaking around 30~au, with some additional diffuse DCN emission present at larger radii, while DCO+ is present in a broad structured ring that extends past the pebble disk. Based on parametric disk abundance models, these emission patterns can be explained by a near-constant DCN abundance exterior to the cavity, and an increasing DCO+ abundance with radius. There appears to be an active deuterium fractionation chemistry in multiple disk regions around TW Hya, but not in the cold planetesimal-forming midplane and in the inner disk. More observations are needed to explore whether deuterium fractionation is actually absent in these latter regions, and if its absence is a common feature, or something peculiar to the old TW Hya disk.
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