发表机构
Space Research Institute, Austrian Academy of Sciences; Leibniz Institute for Astrophysics Potsdam (AIP); Space Research Organisation Netherlands; Department of Astronomy, University of Wisconsin-Madison（奥地利科学院空间研究所; 波茨坦莱布尼茨天体物理研究所; 荷兰空间研究组织; 威斯康星大学麦迪逊分校天文学系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
利用 HD 143006 内盘投下的阴影，结合 ALMA 观测与 ProDiMo 模型，发现其外盘 C/O 略大于 1，并揭示慢热弛豫与紫外解吸对谱线形成的关键作用。
AI 中文摘要
T Tauri 星 HD 143006 的内盘是倾斜的，并在外盘的大部分区域投下宽阔的阴影。我们利用这一特殊的几何结构来研究恒星紫外（UV）辐照对盘化学、温度和谱线形成的影响。我们展示了该盘在 CO、$^{13}$CO、C$^{18}$O、CN、HCN、HCO$^+$、CS 和 C$_3$H$_2$ 中的新 ALMA 观测数据，并将这些数据与先前发表的数据相结合，得到一个丰富的数据集，该数据集使用 ProDiMo 模型对受照射侧和阴影侧进行建模，其中包含一个可选的倾斜内盘，以部分阻挡恒星对外盘的照射。观测到的受照射侧和阴影侧之间的谱线通量对比度很小。我们通过引入“平衡模型”来解释这一点，该模型考虑了在阴影内外轨道运行的气体团的缓慢加热/冷却弛豫。我们拟合了盘两半部分所有 14 条 ALMA 谱线的径向强度分布、20$\\,\mu$m 以外的 SED 以及两个 ALMA 连续谱图像，在一个组合模型中总体约化 $\chi$ 约为 2.3。由于气体升温缓慢，受照射侧的谱线强度仅略有增加，尽管快速的紫外光化学显著降低了可观测的分子浓度。对于探测气体和尘埃温度耦合的更深层的 N$_2$H$^+$ 和 CS 谱线，NH$_3$ 和 H$_2$S 等冰的缓慢紫外解吸起着关键作用。这可能导致这些谱线在阴影侧变亮。HD 143006 外盘中的碳氧比略大于 1（$\sim 1.05$）。拟合出的盘质量低至 $0.0012 M_{\odot}$，但在重新调整盘形状、尘埃和气体加热/冷却参数后，可以获得固定盘质量为 $0.021 M_\odot$ 的几乎同样好的拟合模型。（删节）
英文摘要
The inner disk of the T Tauri star HD 143006 is inclined and casts a broad shadow on a large portion of the outer disk. We use this extraordinary geometry to study the impact of stellar ultraviolet (UV) irradiation on disk chemistry, temperature, and line formation. We present new ALMA observations of this disk in CO, $^{13}$CO, C$^{18}$O, CN, HCN, HCO$^+$, CS and C$_3$H$_2$ and combine these with previously-published data to get a rich dataset, which is modeled with ProDiMo models for the illuminated and shadowed side by including an optional inclined inner disk to partially block stellar illumination of the outer disk. The observed line flux contrasts between the illuminated and the shadowed disk sides are small. We explain this by introducing ``equilibrated models'' which consider a slow heating/cooling relaxation of gas parcels orbiting in and out of the shadow. We fit the radial line intensity profiles of all 14 ALMA lines for both halves of the disk, the SED beyond 20$\,μ$m, and two ALMA continuum images, with an overall reduced $χ$ of about 2.3, in one combined model. Line intensities only increase slightly on the illuminated side because the gas warms up slowly, although fast UV photochemistry significantly reduces the observable molecular concentrations. For the lines of N$_2$H$^+$ and CS, which probe deeper layers where the gas and dust temperatures are coupled, slow UV-desorption of ices such as NH$_3$ and H$_2$S plays a crucial role. This can result in a brightening of these lines on the shadowed side. The carbon-to-oxygen ratio in the outer disk of HD 143006 is slightly greater than one ($\sim 1.05$). The disk mass is fitted to be as low as $0.0012 M_{\odot}$, but almost equally well-fitting models with a fixed disk mass of $0.021 M_\odot$ can be obtained after re-adjusting the disk shape, dust, and gas heating/cooling parameters. (abridged)
CommentsA&A accepted; version prior to language editing. 32 pages, 21 figures
