How were the elements made in the first stars?

拟议的研究计划有条不紊地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、超新星物理和前身、太阳前颗粒和相互作用的双星等领域实现了一系列科学目标。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。我们能够产生一些独特的天体物理模拟，例如第一个NuGrid产额数据集，白矮星前恒星燃烧的流体动力学模拟，双简并后恒星的核合成等等。**因此，我们现在制定了新的目标，这将再次构成通过高保真模拟理解天体物理过程的根本进步。具体地说，我们建议消除传统的球对称恒星演化在描述多维过程方面的一些限制。有了一个原创的、创新的、新的工具，我们将能够解决一些紧迫的问题，即早期宇宙中形成的恒星中的元素是如何构成的。**例如，我们将首次能够对贫金属星的流体动力对流和核合成过程进行现实模拟，这些恒星拥有一种特殊的、鲜为人知的中间中子俘获过程。这一中间过程或I过程的丰度特征在异常的贫金属C增强的S+r星中被观测到。它们是在大约十年前被发现的，它们是我们理解元素是如何在我们的宇宙黎明时期形成的关键。到目前为止，它们非常不寻常的丰度模式一直难以得到令人满意的解释。最近，我们发现了这个谜题的一个明显而吸引人的解决方案。在贫金属的恒星模型中，当富氢包层物质对流混合在更热、更深的对流不稳定层中时，会遇到对流反应燃烧条件(类似于喷气发动机中的情况，除了核燃烧而不是化学燃烧)，那里有丰富的新鲜制造的12C。在这样的条件下，可以实现公认的慢(S)过程和快(R)过程之间的中子密度。有了我们的新模拟能力，我们能够在超级渐近巨星分支中为这个I过程确定一个可能的地点。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，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。在进一步的第二步中，我们计划利用我们在大规模后处理核合成模拟中的经验，创建一种可以在三维模拟表示中确定核合成的设施。**虽然我们将继续使用我们现有的非常强大的模拟工具，例如NuGrid模拟代码，以生成数据集，以便立即应用于解释天文观测(例如，通过星系化学演化模型)，但我们建议为我们的计划提供充足的资金，以便创建新一代模拟工具，使我们能够解决现有和未来观测数据产生的未决问题。

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.