发表机构
Jet Propulsion Laboratory, California Institute of Technology; Columbia University; Observatoire de Paris, Université PSL, CNRS, Sorbonne Université; Instituto de Física Fundamental (CSIC)（加州理工学院喷气推进实验室; 哥伦比亚大学; 巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学; 基础物理研究所（西班牙高等科学研究委员会））
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究分析赫歇尔卫星对S140光子主导区的光谱数据，约束水蒸气丰度与正仲比，发现水主要存在于深层低温区域，且正仲比符合局部气体温度下的LTE假设。
AI 中文摘要
我们分析了档案中的远红外至亚毫米赫歇尔PACS、SPIRE和HIFI光谱观测数据，以约束S140光子主导区（PDR）中的水蒸气丰度和正仲比。针对高质量原恒星IRS1，PACS和SPIRE仪器探测到52条谱线，其中包括15条水谱线。PDR建模表明该区域的紫外辐射场G0约为1×10^3哈宾单位，热气体压力为5×10^8 K cm^-3。模型严重低估了高J CO谱线的强度，这可能表明除了紫外辐射气体外，沿视线方向还存在与外向流相关的热激波气体。PACS和SPIRE光谱仪的光谱分辨率不足以区分PDR和激波的贡献。PDR模型进一步表明，光学厚基态水谱线主要示踪PDR的表面层。该区域的气体温度预计约为800 K，相对于氢核的水丰度达到约10^-5。然而，大部分气相水位于PDR内部更深的屏蔽区域，气体温度约为24 K，气相H2O丰度约为10^-7。将观测到的IRS1水谱线通量与PDR模型预测进行比较，未发现与模型中假设的局部气体温度下LTE正仲比存在偏差的证据。赫歇尔仪器的灵敏度不足以测量S140分子云表面外部照射的侧向PDR中的水正仲比。此类观测将有可能通过目前正在开发的下一代远红外光谱空间任务实现。
英文摘要
We analyzed archival far-infrared to submillimeter Herschel PACS, SPIRE, and HIFI spectroscopic observations of the S140 photon dominated region (PDR) to constrain the water vapor abundance and ortho-para ratio in this region. Toward the high-mass protostar IRS1, 52 spectral lines, including 15 water lines, are detected with the PACS and SPIRE instruments. PDR modeling suggests a UV radiation field G0 ~ 1 x 10^3 Habing units, and a thermal gas pressure of 5 x 10^8 K cm^-3 in this region. The models strongly underestimate intensities of high-J CO lines, which may indicate the presence of hot shocked gas associated with outflows along the line of sight, in addition to the UV irradiated gas. The spectral resolution of the PACS and SPIRE spectrometers is insufficient to separate the PDR and shock contributions. The PDR models further suggest that optically thick ground-state water lines trace primarily surface layers of the PDR. The gas temperature in this region is predicted to be ~ 800 K and the water abundance with respect to hydrogen nuclei reaches ~ 10^-5. However, the bulk of gas-phase water is located in a more shielded region, deeper inside the PDR, with a gas temperature ~ 24 K, and a gas-phase H_2O abundance of ~ 10^-7. A comparison of the observed water line fluxes toward IRS1 with PDR model predictions shows no evidence for departures from the LTE ortho-para ratio at the local gas temperature, which is assumed in the models. The sensitivity of the Herschel instruments was insufficient to measure the water ortho-para ratio toward the externally illuminated edge-on PDR at the surface of the S140 molecular cloud. Such observations will be possible with the next generation far-infrared spectroscopic space missions currently in development.
CommentsAccepted for publication in Astronomy & Astrophysics
