Modeling White-Dwarf Merger Events: The R Coronae Borealis Stars

恒星合并是一种神秘的现象，它在很小的体积和短暂的时间内包含了广泛的物理过程。在合并中，两颗恒星的结构和演化受到剧烈的干扰而合二为一。恒星合并是一种自然实验，可以帮助天文学家回答有关恒星演化的重要问题。北冕R （RCB）恒星是罕见的、缺乏氢、富含碳、被星周尘埃包围的超巨星。有人提出，在RCB恒星和某些被称为Ia型超新星（SNe）的恒星爆炸之间可能存在联系，当两颗白矮星（wd）合并时，这两类恒星都会出现。路易斯安那州立大学（LSU）的一个研究小组计划使用计算机模型来模拟RCB恒星的演化，以详细研究RCB恒星，以回答有关它们的形成、寿命和演化为不同类型恒星的问题。通过研究这种类型的WD合并，路易斯安那州立大学的研究小组还将有助于更好地了解Ia型超新星的起源，这对理解宇宙的膨胀非常重要。研究人员将继续参与外展工作，包括公众观测之夜和讲座，让业余天文学家参与研究项目，开发创新的远程学习和在线天文学课程，这些课程将覆盖大量公众。他们还在培训下一代天文学研究人员，并努力增加天文学的多样性。路易斯安那州立大学的研究小组计划利用他们新的自引力流体力学代码和MESA（一个一维恒星演化模块）的组合来模拟RCB恒星的演化。他们的新代码Octo-tiger/HPX是一个具有牛顿引力的三维、有限体积自适应网格细化（AMR）流体力学代码。该小组将开发一个辐射传输模块，并整合一个有限的核反应网络。Octo-tiger/HPX在多核高性能计算机上并行执行，这将允许它们探测参数空间的新领域，如更高的空间分辨率，更大的网格和多个动态时间尺度。这项工作的结果不仅将扩大对导致RCB恒星的恒星合并事件的理解，而且还将揭示许多其他相关物体，包括接触双星，蓝离散星，热亚矮星，红新星，大质量恒星合并，x射线双星，灾难性变量，短伽马射线暴和Ia型超新星，合并和共同包层演化可能起着至关重要的作用。在天体物理学领域之外，这项研究有望为其他需要高度线性和角动量守恒的流体模拟、核模拟、多物理场模拟和AMR技术铺平道路。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。

Stellar mergers are mysterious phenomena that pack a broad range of physical processes into a small volume and a fleeting time duration. In a merger, two stars become one as their structures and evolution are violently perturbed. A stellar merger is a natural experiment that can help astronomers answer important questions about stellar evolution. The R Coronae Borealis (RCB) stars are rare, hydrogen-deficient, carbon-rich, supergiant stars surrounded by circumstellar dust. It has been suggested that there is a possible connection between the RCB stars and certain stellar explosions called Type Ia supernovae (SNe), where both classes arise when two white dwarf stars (WDs) merge. A research group at Louisiana State University (LSU) plans to study RCB stars in detail using computer models to simulate the evolution of an RCB star to answer questions about their formation, lifetime, and evolution into a different type of star. By investigating this type of WD merger, the LSU group will also help to better understand the origin of Type Ia SNe, which are important for understanding the expansion of the universe. The researchers will continue to participate in outreach efforts including public observing nights and talks, involving amateur astronomers in research projects and developing innovative distance learning and online astronomy courses that will reach large numbers of the public. They are also training the next generation of astronomy researchers and working to increase diversity in astronomy.The LSU group plans to simulate the evolution of an RCB star using a combination of their new self-gravitating hydrodynamics code and MESA, a 1-D stellar evolution module. Their new code, Octo-tiger/HPX, is a 3-D, finite-volume adaptive mesh refinement (AMR) hydrodynamics code with Newtonian gravity. The group will develop a radiation transport module and incorporate a limited nuclear reaction network. Octo-tiger/HPX is parallelized for execution on multi-core high performance computers, which will allow them to probe new areas of parameter space such as much higher spatial resolution, much larger grids, and multiple dynamical time scales. The results of this work will not only broaden the understanding of stellar merger events that lead to RCB stars, but will also shed light on many other related objects for which mergers and common envelope evolution may play a crucial role, including contact binaries, blue stragglers, hot subdwarfs, red novae, massive star mergers, X-ray binaries, cataclysmic variables, short gamma-ray bursts, and Type Ia supernovae. Beyond the astrophysics domain, the research has promise to pave the way for other fluid simulations requiring a high degree of linear and angular momentum conservation, nuclear simulation, multi-physics simulation, and AMR techniques.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.