外部光蒸发如何改变内盘的化学成分
How external photo-evaporation changes the chemical composition of the inner disc
AI总结：
本研究结合FRIED网格扩展chemcomp代码，探究外部光蒸发对原行星内盘化学成分的影响，发现因卵石快速向内漂移，受光蒸发盘与孤立盘内盘化学性质相似，符合JWST观测结果。
摘要：
恒星大多形成于星团中，邻近恒星会影响原行星盘的演化。除引力相互作用外，外部光蒸发也能塑造这些原行星盘。根据光蒸发强度的不同，原行星盘可在1-2百万年（Myrs）内被摧毁，或是经历更缓慢的演化。我们使用chemcomp代码（整合了含卵石漂移与蒸发过程的黏性原行星盘演化模型）来计算原行星盘的化学成分，并基于FRIED网格对该代码进行扩展，纳入了外部光蒸发效应。初始阶段，原行星盘仅靠黏性演化，内盘的碳氧比（C/O ratio）会因向内漂移并蒸发的水冰卵石而降低；随着时间推移，由于水蒸气吸积到恒星上且富碳气体向内迁移，碳氧比会上升。当外部光蒸发启动后，外盘会被驱散，但内盘的化学演化仍遵循纯黏性原行星盘的演化规律，因为大多数卵石在1百万年内就已向内漂移完毕。在低黏性条件下，内盘的碳氧比在被光蒸发驱散前始终低于太阳值（sub-solar）；在高黏性条件下，若原行星盘能存活数百万年，由于水蒸气吸积更快且富碳气体向内迁移，碳氧比可达到高于太阳值（super-solar）的水平。在两种黏性条件下，由于卵石的快速向内漂移，内盘化学成分与纯黏性模型相比均无显著差异。我们的模型预测，受外部光蒸发影响的原行星盘与孤立原行星盘的内盘化学性质应是相似的，这与JWST的观测结果一致。
英文摘要：
Stars mostly form in clusters where neighboring stars can influence proto-planetary disc evolution. Besides gravitational interactions, external photoevaporation can shape these discs. Depending on the strength of photoevaporation, discs can be destroyed within 1-2 Myrs or more gradually. We use the chemcomp code, incorporating a viscous disc evolution model with pebble drift and evaporation, to calculate the chemical composition of protoplanetary discs. This code is extended to include external photoevaporation based on the FRIED grid. Initially, the disc evolves purely viscously, with the inner disc's C/O ratio decreasing due to inward drifting and evaporating water ice pebbles. Over time, the C/O ratio increases as water vapor accretes onto the star and carbon-rich gas migrates inward. Once external photoevaporation starts, the outer disc disperses, but the inner disc's chemical evolution follows that of a purely viscous disc, as most pebbles have already drifted inward within 1 Myr. At low viscosity, the inner disc's C/O ratio remains sub-solar until dispersion by photoevaporation. At high viscosity, the C/O ratio can reach super-solar values, due to faster accretion of water vapor and inward migration of carbon-rich gas, provided the disc survives a few Myrs. In both cases, there is no significant difference in the inner disc's chemical composition compared to a purely viscous model due to the rapid inward drift of pebbles. Our model predicts that inner disc chemistry should be similar for discs subject to external photoevaporation and isolated discs, consistent with JWST observations.
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