原行星盘中尘埃动力学与气体化学联合演化的数值模拟

Protoplanetary disks are disk-shaped gas and dust distribution surrounding low-to-mid mass young stars. In the recent years spectral line observation of molecules including CO and H2O with telescopes such as ALMA and Herschel have shown significant discrepancy with theoretical models. The applicant and collaborators proposed that this discrepancy arose because the effect of dust evolution on gas phase chemistry has been neglected in those models. By adjusting the distribution of carbon and oxygen elements empirically, the observational data can be satisfactorily fitted. However, direct simulation of the coupled evolution of dust and gas chemistry from first principles has not been conducted yet. The current proposed research will numerically study the coupled evolution of dust grains and gas chemistry, using the operator-splitting method to solve the equations. This new model will give a more physically consistent interpretation of observational data, and make predictions for future observations. More accurate dust and gas molecule distribution in protoplanetary disks will be obtained from the simulations. Since planets get their early composition from protoplanetary disks, the model data can be compared with observations of exoplanet atmospheres. Furthermore, the evolution of dust grains can affect the heating and cooling rates of gas through its effect on gas composition, hence will also have an effect on the dispersal of protoplanetary disks.

原行星盘是年轻中低质量恒星周围的盘状物质分布，由气体和尘埃组成。近年来用ALMA、Herschel等观测设备获取的包括CO、H2O在内的多种原行星盘分子谱线数据与理论模型之间存在显著差异。本项目负责人与合作者提出用尘埃演化对气体化学的影响来解释这种差异，并以此为基础用唯象模型调整碳元素和氧元素的分布给出了较好的定量解释。但是，从第一性原理出发对尘埃与气体化学耦合演化的直接模拟，迄今还没有人做过。本研究使用数值模拟方法把原行星盘的尘埃演化与气体化学耦合，使用算符分解法求解相关方程，验证尘埃演化对气体化学的影响，对已有观测数据给出物理上自洽的解释，并预测未来的观测数据。新的模型会给出原行星盘更准确的尘埃和气体分布，这些尘埃和气体是行星早期成分的来源，可以与系外行星大气的观测印证。另外，尘埃动力学演化会通过改变气体化学成分来间接改变盘的加热和冷却率，因此对盘的气体消散过程也有影响。

原行星盘中的气体化学与尘埃演化耦合，而尘埃的演化是行星子形成的重要环节。气体化学与尘埃演化的联合模拟需要功能更加灵活、计算更高效的软件，为此我们研发了新的化学模拟工具chempl。基于这套工具研究了分子云形成初期的化学演化和同位素化学，相关结果支持了分子云快速演化的理论。通过化学模拟发现银河系中心高能活动对周边复杂有机分子的分布影响显著。在本项目的支持下，还发现了大质量恒星形成早期多次吸积爆发事件，分析了纤维状分子云的朝向和质量分布，评估了使用未来观测设备如CSST和SKA探测星际分子的可能性。