AI 中文总结
通过SMA观测5个T Tauri星的过渡盘，发现HNC流量比非过渡盘模型预测高3-10倍，HNC-HCN柱密度比与盘质量正相关，表明过渡盘空腔与HNC高效生成相关。
AI 中文摘要
原行星盘的物理与化学条件塑造了新生行星系统的特性。HCN-HNC异构体对的线比率与相对丰度非常适合用于追踪这些气体条件，因为异构体化学与发射气体的基础温度、元素丰度及辐射环境相关。虽然HCN会发射明亮的谱线，且在盘中被频繁观测到，但较暗的HNC谱线却很少成为观测目标，这使得我们无法校准HNC与HCN的比率以作为盘特性的示踪剂。在此，我们报告了对5个围绕T Tauri星的过渡盘（GM Aur、J1604、LkCa 15、GG Tau和V4046 Sgr）的新亚毫米波阵列（Submillimeter Array, SMA）观测结果，覆盖了HCN和HNC的J=3-2与J=4-3谱线。我们在每个源中都检测到了至少一条HCN和HNC的谱线，并测量得到盘积分的HNC与HCN流量比率约为0.1-0.7，柱密度比率约为0.1-0.4。对于所有源，测得的HNC流量比全（非过渡）盘模型的预测值高出约3-10倍，而HCN流量则看起来较为典型。过渡盘中HNC相对于HCN的相对亮度强烈表明，空腔的存在与HNC的高效生成之间存在关联。我们使用DM Tau过渡盘的化学模型证实了这一趋势，表明HNC的生成与破坏和辐射环境相关。在我们的样本中，盘积分的HNC与HCN柱密度比率与盘气体温度无关联，但与盘质量呈正相关，原因是质量更大的盘中存在更大的冷气体储库，其中HNC丰度更高。
英文摘要
The physical and chemical conditions of protoplanetary disks shape the properties of nascent planetary systems. The line ratios and relative abundances of the HCN-HNC isomer pair are well-suited for tracing these gas conditions, since isomer chemistry is linked to the underlying temperature, elemental abundances, and irradiation environment of the emitting gas. While HCN emits bright lines regularly observed in disks, the fainter HNC lines are targeted significantly less often, precluding our ability to calibrate the HNC-to-HCN ratio as a tracer of disk properties. Here, we present new Submillimeter Array observations of five transition disks around the T Tauri stars GM Aur, J1604, LkCa 15, GG Tau, and V4046 Sgr, covering the J=3-2 and J=4-3 lines of HCN and HNC. We detected at least one line of both HCN and HNC in each source and measured disk-integrated HNC-to-HCN flux and column density ratios of $\approx$0.1-0.7 and 0.1-0.4, respectively. For all sources, measured HNC fluxes exceed predictions from models of full (non-transition) disks by $\approx$3-10x, while HCN fluxes appear typical. The relative brightness of HNC vs. HCN in transition disks strongly suggests a link between the presence of a cavity and efficient HNC production. We corroborate this trend using chemical models of the DM Tau transition disk, showing HNC production and destruction are connected to the radiation environment. In our sample, disk-integrated HNC-to-HCN column density ratio shows no trend with disk gas temperature but positively correlates with disk mass due to increased HNC abundance in the larger reservoirs of cooler gas in more massive disks.
Comments23 pages, 11 figures, accepted for publication in ApJ
