标题： TW Hya罗塞塔石项目IV：富含烃类的盘大气层 显示英文标题

标题： The TW Hya Rosetta Stone Project IV: A hydrocarbon rich disk atmosphere

摘要： 将行星形成盘的组成与气态巨行星大气的组成联系起来，特别是通过C/O比值，是盘化学的关键目标之一。已鉴定小碳氢化合物如$\rm C_2H$和$\rm C_3H_2$作为C/O的示踪剂，因为在高C/O条件下它们会大量形成。我们展示了来自TW Hya罗塞塔石项目（旨在以$15-20$天文单位分辨率绘制TW Hya盘中常见分子化学分布的计划）的分辨率为$\rm C_3H_2$的观测结果。 结合档案数据，这些观测构成了最广泛的多线集，涵盖了正交和顺式自旋异构体的盘状结构，并跨越了广泛的能量范围，达 $E_u=29-97$ K。我们发现 $\rm C_3H_2$ 的正交到顺式的比例在整个发射范围内都与 3 一致，并且两种 $\rm C_3H_2$ 异构体的总丰度为每个氢原子 $(7.5-10)\times10^{-11}$，或者说是同一来源中先前发表的 $\rm C_2H$ 丰度的 $1-10$%。 我们发现，$\rm C_3H_2$来自一个接近表面的层，其深度不超过$z/r=0.25$。 我们的观测结果与TW Hya中气相C/O存在显著径向变化一致，并在外侧$\sim30$天文单位处出现急剧增加。 即使我们没有直接追踪中平面，但如果行星通过例如经向环流从表面吸积物质，那么这种变化应该会反映在正在形成的行星上。 或许有趣的是，HR 8799行星系统中的巨行星大气中C/O比值也显示出递增梯度。 尽管这些恒星差异很大，但盘中的碳氢化合物环很常见，因此我们的结果与HR 8799年轻行星仍保留其母盘挥发性化学成分印记是一致的。 显示英文摘要

摘要： Connecting the composition of planet-forming disks with that of gas giant exoplanet atmospheres, in particular through C/O ratios, is one of the key goals of disk chemistry. Small hydrocarbons like $\rm C_2H$ and $\rm C_3H_2$ have been identified as tracers of C/O, as they form abundantly under high C/O conditions. We present resolved $\rm C_3H_2$ observations from the TW Hya Rosetta Stone Project, a program designed to map the chemistry of common molecules at $15-20$ au resolution in the TW Hya disk. Augmented by archival data, these observations comprise the most extensive multi-line set for disks of both ortho and para spin isomers spanning a wide range of energies, $E_u=29-97$ K. We find the ortho-to-para ratio of $\rm C_3H_2$ is consistent with 3 throughout extent of the emission, and the total abundance of both $\rm C_3H_2$ isomers is $(7.5-10)\times10^{-11}$ per H atom, or $1-10$% of the previously published $\rm C_2H$ abundance in the same source. We find $\rm C_3H_2$ comes from a layer near the surface that extends no deeper than $z/r=0.25$. Our observations are consistent with substantial radial variation in gas-phase C/O in TW Hya, with a sharp increase outside $\sim30$ au. Even if we are not directly tracing the midplane, if planets accrete from the surface via, e.g., meridonial flows, then such a change should be imprinted on forming planets. Perhaps interestingly, the HR 8799 planetary system also shows an increasing gradient in its giant planets' atmospheric C/O ratios. While these stars are quite different, hydrocarbon rings in disks are common, and therefore our results are consistent with the young planets of HR 8799 still bearing the imprint of their parent disk's volatile chemistry.