CDS&E: 3-D Stellar Hydrodynamics of Convective Boundary Mixing and Shell Mergers in Massive Stars

恒星的演化以及它们作为白矮星、白矮星超新星、中子星或黑洞的最终命运仍然是天文学研究的中心。这个问题涉及到时域天文学、超新星研究、核天体物理学、星系化学演化、星震学、恒星群以及早期宇宙中恒星和结构的形成和演化等多种研究课题。然而，对流的基本宏观恒星物理过程仍然知之甚少。虽然有一些很好的理论，尽管相当简单，但惊人的准确，现实的研究必须依赖于计算密集的模拟。这就是这个项目将启用和执行的。它将对恒星演化理论产生重大影响，提供广泛适用的前沿技术和创新方法。该研究支持一名研究生和最多三名本科生，研究结果将用于课程教学。具体细节，特别是对对流壳层合并的研究，如大质量恒星的C和o燃烧壳层，以及对流边界混合，只能在复杂的三维（3D）流体动力学模拟中真实地捕捉到。该项目将以先前的工作为基础，实现三个主要目标：(1)验证对流边界混合的一维模型，使用与接近生命终点的大质量恒星相关的简短3D恒星流体动力学模拟；(2)利用(1)的模型与三维模拟相结合，评估两个彼此正上方的对流壳层何时可以合并；(3)对于壳层合并的情况，利用三维流体动力学模拟来研究邻近壳层交换化学丰度混合物的情况。先前的一维研究表明，o型燃烧壳层上方的对流区可以吸收足够的物质到达c型燃烧壳层。这可能会导致像钾、钪和氯这样的奇数- z元素产生更多的量。一系列简短的3D模拟与较长的1D模拟交替进行，将详细展示壳合并过程的方法和最终结果。将组织并提供对流边界混合结果的大型数据库，以及挖掘、分析和显示结果的工具，以使更大的社区能够进行意想不到的研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The evolution of stars and their ultimate fate as white dwarfs, white dwarf supernovae, neutron stars, or black holes remains at the center of research in astronomy. This question relates to diverse research topics in time domain astronomy, supernova research, nuclear astrophysics, galactic chemical evolution, asteroseismology, stellar populations, and the formation and evolution of stars and structure in the early universe. However, the fundamental macroscopic stellar physics process of convection remains poorly understood. Although there is some good theory, surprisingly accurate despite being rather simplistic, realistic studies must rely on computationally intensive simulations. That is what this project will enable, and perform. It will have a large impact on stellar evolution theory, providing cutting edge techniques and innovative methods of wide applicability. The study supports one graduate and up to three undergraduate students, and the results will be used in course teaching.The details, especially the study of mergers of convective shells, such as the C- and O-burning shells of massive stars, as well as convective boundary mixing, can only be realistically captured in complex three-dimensional (3D) hydrodynamics simulations. This project will build on prior work to pursue three main objectives: (1) validation of a 1D model of convective boundary mixing, using brief 3D stellar hydrodynamics simulations relevant to massive stars near the ends of their lives; (2) assessment of when two convective shells right on top of each other can in fact merge, using the model from (1) combined with 3D simulation; and (3) for shell merger cases, use 3D hydrodynamical simulations to study when nearby shells exchange their chemical abundance mixtures. Prior studies in 1D indicate that the convection zone above the O-burning shell could incorporate enough material from above it to reach the C-burning shell. This could cause odd-Z elements like potassium, scandium, and chlorine to be produced in greater abundance. A sequence of brief 3D simulations alternating with longer 1D simulations will show in detail the approach to, and ultimate result of, the shell merger process. The large database of results on convective boundary mixing will be organized and made available, together with the tools that mine it, analyze it, and display its results, to enable unanticipated research by the greater community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.