JWST原初多环芳烃项目：具有广泛脂肪族取代的芳香骨架同时解释了芳香和脂肪族发射
The JWST Proto-PAH project: Aromatic backbones with extensive aliphatic substitution account for both the aromatic and aliphatic emission
另 4 家 · 查看机构详情
- The University of Western Ontario（韦仕敦大学）
- Institute for Earth and Space Exploration, The University of Western Ontario（韦仕敦大学地球与太空探索研究所）
- Space Telescope Science Institute（太空望远镜科学研究所）
- University of North Carolina, Chapel Hill（北卡罗来纳大学教堂山分校）
- Boston College（波士顿学院）
- University of Texas at Austin（德克萨斯大学奥斯汀分校）
- Universitat de Barcelona (UB)（巴塞罗那大学）
机构由 AI 辅助整理，请以论文原文为准。
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中文总结 AI 辅助
基于JWST光谱，发现富碳后AGB星中芳香与脂肪族发射同源于芳香骨架上的广泛脂肪族取代分子，而非传统PAH。
中文摘要 AI 辅助
我们发现，四颗具有D类发射的富碳后渐近巨星分支恒星中的芳香和脂肪族发射带源于同一载体群：芳香骨架上的广泛脂肪族修饰，即具有连贯芳香骨架和异常高脂肪族含量的分子。这一结论基于JWST NIRSpec和MIRI/MRS光谱，覆盖2.88-28.7微米。脂肪族3.4微米特征强于芳香3.3微米特征，逆转了典型多环芳烃（PAH）发射源中所见的比例。如果芳香发射源于名义上的PAH，那么3.3微米特征——在之前的观测中不可用——连同中红外芳香特征，将约束它们为大尺寸（大于约碳原子数）、致密且至少部分电离。这些性质预测了强的8.6微米特征。然而，在所有四个源中8.6微米特征弱或缺失，排除了PAH作为芳香发射的来源。相反，发射必须源于与脂肪族发射相同的载体。6.9微米特征的位置和展宽的11-14微米面外发射独立支持这一点。CH2和CH3特征强度在样本中变化，D2类源显示出更高的CH3含量。这些载体比行星状星云和星际介质中的PAH更具脂肪族特性。然而，它们保留了产生其芳香特征的芳香骨架。
英文摘要
We find that the aromatic and aliphatic emission bands in four carbon-rich post-asymptotic giant branch stars with class D emission arise from a single carrier population: extensive aliphatic decoration of an aromatic skeleton, i.e. molecules with a coherent aromatic backbone and an unusually high aliphatic content. This conclusion is based on JWST NIRSpec and MIRI/MRS spectroscopy, covering 2.88-28.7um. The aliphatic 3.4um feature is stronger than the aromatic 3.3um feature, reversing the ratio seen in sources with typical polycyclic aromatic hydrocarbon (PAH) emission. If the aromatic emission arose from nominal PAHs, the 3.3um feature - unavailable in previous observations - together with the mid-infrared aromatic features, would constrain them to be large (greater than about carbon atoms), compact, and at least partially ionized. These properties predict a strong 8.6um feature. However, the 8.6um feature is weak or absent in all four sources, ruling out PAHs as the source of the aromatic emission. Instead, the emission must arise from the same carriers as the aliphatic emission. The position of the 6.9um feature and the broadened 11-14um out-of-plane emission independently support this. The CH2 and CH3 feature strengths vary across the sample, with the class D2 sources showing higher CH3 content. These carriers are far more aliphatic than the PAHs of planetary nebulae and the interstellar medium. However, they retain the aromatic skeleton that produces their aromatic features.
