3-D Stellar Hydrodynamics Simulations for Convective-Reactive Nucleosynthesis

天文观测正在探索宇宙的早期阶段，在这个阶段，星系发展和融合，宇宙结构的形成和演化到今天。这个故事的一个重要部分是星系的化学演化。恒星中元素的形成及其随后的扩散是结构形成和演化的有力示踪剂。这个项目将模拟蓝水在恒星内部深处的过程，这些过程在它们产生的重元素中起着重要作用。这些过程是由对流区边界的气体混合驱动的，它可以将新的燃料带入对流区，将它们带到更热的区域，在那里它们燃烧得非常快，并在一种特殊的对流反应状态下激活核反应网络。在这种情况下，反应核在与反应发生时大致相同的时间尺度上由湍流对流传递，因此，即使在统计意义上，也可能导致与球对称的显著偏离。该项目将使用Blue Waters的千万亿级功能以3D形式模拟这些简短事件。这个项目我们将建立在Blue Waters早期工作的基础上，研究一个过程，在这个过程中，大质量恒星中的o壳对流区可以工作到上面c壳对流区的底部，导致碳燃料的摄入和两个燃烧壳的最终合并。该项目将通过跟踪大量核同位素的浓度，并在空间和时间上降低分辨率的4-D网格上计算它们的相互作用，来计算由此产生的核合成。为了精确地推进湍流对流流动并计算对流区边界处的燃料携带量，需要一个精细的网格。该研究将跟踪细网格上最重要的物种，但将在粗网格上表示大量的核反应，这些核反应的能量释放较小，对流动的反作用最小。该项目将生成一个大型数据库，其中包含恒星内部对流边界混合蓝水的三维模拟结果。该项目打算组织这个数据库，以便模拟代码可以自动挖掘它，并将其与各种可能有用的混合过程的一维模型进行比较。就更广泛的影响而言，该项目将使这个数据库和工具以有用的形式联机提供给社区，从而使许多其他人能够进行研究。此外，该项目将与NuGrid合作，确保结果被纳入社区可用的数据集，用于早期宇宙中星系和结构的化学演化模拟。

Astronomical observations are now probing the early stages of the universe, in which galaxies developed and merged, and the formation of structure in the universe and its evolution to the present era was set in motion. An important part of this story is the chemical evolution of galaxies. The formation of the elements in stars and their subsequent dispersal are powerful tracers of structure formation and evolution. This project will simulate on Blue Waters processes deep inside stars that play an important role in the heavy elements they generate. These processes are driven by mixing of gases at the boundaries of convection zones, which can bring new fuels into a convection zone, carrying them down into much hotter regions where they burn very rapidly and activate nuclear reaction networks in a special convective-reactive regime. In this regime, reacting nuclei are transported by the turbulent convection flow on about the same timescale as the reactions take place, so that significant departures from spherical symmetry, even in a statistical sense, can result. This project will use the petascale capabilities of Blue Waters to simulate these brief events in 3D.This project we will build on earlier work on Blue Waters to study a process where the O-shell convection zone in a massive star can work its way to the base of the C-shell convection zone above, leading to ingestion of carbon fuel and an ultimate merger of the two burning shells. The project will compute the resulting nucleosynthesis by following the concentrations of a large number of nuclear isotopes and computing their interactions on a 4-D grid of reduced resolution in space and time. A fine grid is required to accurately advance the turbulent convection flow and to compute the amount of fuel entrained in it at the convection zone boundary. The study will follow the most important species on this fine grid, but will represent on the coarser grid the large number of nuclear reactions from which energy release is minor and has minimal back reaction on the flow. This project will generate a large database of results from the 3-D simulations on Blue Waters of convective boundary mixing in stellar interiors. The project intends to organize this database so that the simulation codes can mine it automatically, comparing it to a variety of potentially useful 1-D models of the mixing process. In terms of broader impacts, the project will make this database and tools available to the community on-line in a useful format, so that it will enable research by many others. In addition, the project will work with the NuGrid collaboration to see that the results are incorporated into data sets that are available to the community for chemical evolution simulations of galaxies and structures in the early universe.