How were the elements made in the first stars?

第一批恒星中的元素是如何形成的？

• 批准号: RGPIN-2014-05762
• 负责人: Herwig, Falk
• 金额: $ 3.06万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=653495
• 关键词: How; were; elements; made; first

The proposed research program is methodically centered in computational stellar and nuclear astrophysics with a range of science goals in areas like stellar archeology, near- field cosmology, supernova physics and progenitors, pre-solar grains and interacting binary stars. During our previous NSERC-funding period we have significantly advanced our computational capabilities in the three areas of our research program: nucleosynthesis, stellar evolution and stellar hydrodynamics. We were able to generate some unique astrophysics simulations, such as the first NuGrid yield data set, hydrodynamic simulations of stellar combustion in pre-white dwarfs, nucleosynthesis in post-double degenerate merger stars and many more.**We do therefore now set out new goals that will again constitute a fundamental advance of understanding astrophysics processes through high-fidelity simulations. Specifically we propose remove some limitations of traditional spherically symmetric stellar evolution in describing multi-dimensional processes. With an original and innovative, new tool we will be able to address some burning question regarding how the elements are made in stars that formed in the early universe. **For example, we will be able to perform for the first time realistic simulations of the hydrodynamic convection and nucleosynthesis processes in metal poor stars, which host a peculiar and little understood intermediate neutron capture process. The abundance signatures of this intermediate or i process are observationally found in the anomalous C-enhanced metal-poor-s+r stars. They have been discovered about a decade ago, and they are key for our understanding of how elements are formed during the dawn of our universe. So far their very unusual abundance patterns have resisted a satisfactory explanation. Very recently we have discovered an obvious and appealing solution to this puzzle. In metal-poor star models convective-reactive combustion conditions (similar to those in a jet engine, except with nuclear instead of chemical burn) are encountered when H-rich envelope material is convectively mixed in hotter, deeper convectively unstable layers where abundant, freshly made 12C is available. In such conditions neutron densities between the well-established slow (s) and rapid (r) process can be realized. With our new simulation capabilities we were able to identify a possible site for this i process in super-Asymptotic Giant Branch stars. We performed some exploratory calculations to determine the general nucleosynthetic signatures of the i process, and we were already able to run some high-resolution stellar hydrodynamics simulations to clarify some aspects of this problem. **In order to test this hypothesis we will build a new simulation capability by interweaving one-dimensional stellar evolution with three-dimensional stellar hydrodynamics. In a further second step we plan to deploy our experience in large-scale post-processing nucleosynthesis simulations to create a facility that can determine the nucleosynthesis in three-dimensional simulation representations. **While we will continue to use our existing and very powerful simulation tools, for example the NuGrid simulation codes, to generate data sets for immediate applications in interpreting astronomical observations (e.g. through galactic chemical evolution models) we propose to fund our program sufficiently in order to create a new generation of simulation tools that will enable us to address open questions that are resulting from existing and future observational data.

拟议的研究计划有条不紊地集中在计算恒星和核天体物理学中，在恒星考古，近场宇宙学，超新星物理学和祖细胞，近极晶粒和相互作用的二元星等领域具有一系列科学目标。在以前的NSERC资助期间，我们在研究计划的三个领域中显着提高了计算能力：核合成，恒星进化和出色的水力学。我们能够生成一些独特的天体物理学模拟，例如第一个NUGRID屈服数据集，白色前矮人中出现恒星燃烧的流体动力模拟，后双变性后的合并后的核合成等等。新目标将再次构成通过高保真模拟理解天体物理学过程的基本进步。具体而言，我们建议在描述多维过程中删除传统球形对称恒星演变的一些局限性。有了一种原始的创新，新工具，我们将能够解决一些关于如何在早期宇宙中形成的恒星中制成的元素的问题。 **例如，我们将能够在金属贫穷恒星中首次对流体动力对流和核合成过程进行现实模拟，这些恒星却含有一个特殊且鲜为人知的中间中子中子捕获过程。该中间或I过程的丰度特征在异常的C增强金属贫困S+R星中观察到。它们大约十年前已经被发现，这是我们了解宇宙曙光期间元素如何形成的关键。到目前为止，他们非常不寻常的丰富模式已经抵制了令人满意的解释。最近，我们发现了这个难题的明显而有吸引力的解决方案。在金属贫穷的星模型中，当H富富富的信封材料以对流混合在更热，更深的对流不稳定的层中时，会遇到对流反应性燃烧条件（类似于喷气发动机中的相似之处，除了用核燃烧而不是化学燃烧）遇到可以使用12C。在这种情况下，可以实现良好的慢速（S）和快速（R）过程之间的中子密度。借助我们的新仿真功能，我们能够在超级反应巨型分支星星中识别我在此过程中进行的一个可能位点。我们进行了一些探索性计算，以确定I过程的一般核合成特征，并且我们已经能够运行一些高分辨率的恒星流体动力学模拟，以阐明该问题的某些方面。 **为了检验这一假设，我们将通过将一维恒星进化与三维恒星流体动力学相结合来构建新的模拟能力。在第二步中，我们计划将我们的经验部署在大规模的后处理核合成模拟中，以创建一个可以在三维模拟表示中确定核合成的设施。 **尽管我们将继续使用现有且非常强大的模拟工具（例如Nugrid仿真代码）来生成数据集，以在解释天文观测（例如通过银河系化学演化模型）来立即应用，但我们建议我们提供足够的资金。为了创建新一代的仿真工具，该工具将使我们能够解决现有和将来的观察数据引起的开放问题。