How were the elements made in the first stars?

拟议的研究计划以计算恒星和核天体物理学为中心，在恒星考古学、近场宇宙学、超新星物理学和祖先、前太阳颗粒和相互作用双星等领域有一系列科学目标。在我们之前的nserc资助期间，我们在研究计划的三个领域显著提高了我们的计算能力：核合成，恒星演化和恒星流体动力学。我们能够生成一些独特的天体物理模拟，例如第一个NuGrid产量数据集，前白矮星中恒星燃烧的流体动力学模拟，后双简并并合恒星的核合成等等。**因此，我们现在确实设定了新的目标，这些目标将再次构成通过高保真模拟理解天体物理学过程的根本进步。我们特别提出消除传统球对称恒星演化在描述多维过程中的一些局限性。有了这个原创的、创新的新工具，我们将能够解决一些亟待解决的问题，比如早期宇宙中形成的恒星中的元素是如何形成的。**例如，我们将能够第一次对金属贫星中的流体动力学对流和核合成过程进行真实的模拟，这是一个特殊的、鲜为人知的中间中子捕获过程。这种中间过程的丰度特征是在异常的c增强金属贫s+r恒星中观测到的。它们大约在十年前被发现，它们是我们理解宇宙初期元素形成的关键。到目前为止，它们非常不寻常的丰度模式还没有一个令人满意的解释。最近，我们发现了一个明显的、吸引人的解决方案。在缺乏金属的恒星模型中，当富h包层材料对流混合在更热、更深的对流不稳定层中，那里有丰富的新鲜生成的12C，就会遇到对流反应燃烧条件（类似于喷气发动机中的情况，只不过是用核燃烧而不是化学燃烧）。在这种条件下，可以实现已确定的慢(s)和快(r)过程之间的中子密度。利用我们新的模拟能力，我们能够在超渐近巨星分支恒星中确定这个i过程的可能位置。我们进行了一些探索性计算来确定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来澄清这个问题的某些方面。**为了验证这一假设，我们将通过将一维恒星演化与三维恒星流体力学交织在一起，建立一种新的模拟能力。进一步第二步我们计划部署我们的经验在大型后处理核合成模拟创建一个工具,可以确定核合成的三维模拟表示。**虽然我们将继续使用我们现有的和非常强大的模拟工具，例如NuGrid模拟代码，为解释天文观测（例如通过星系化学演化模型）的即时应用生成数据集，但我们建议为我们的计划提供足够的资金，以创建新一代的模拟工具，使我们能够解决由现有和未来的观测数据产生的开放问题。

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.