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: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=588600
• 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、太阳前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，我们在我们的研究计划的三个领域显着提高了我们的计算能力：核合成，恒星演化和恒星流体力学。我们能够生成一些独特的天体物理学模拟，例如第一个NuGrid产量数据集，前白矮星恒星燃烧的流体动力学模拟，双简并恒星后的核合成等等。 因此，我们现在制定了新的目标，这些目标将再次构成通过高保真模拟理解天体物理过程的根本进步。具体而言，我们建议消除传统的球对称恒星演化在描述多维过程中的一些限制。有了一个原创和创新的新工具，我们将能够解决一些关于早期宇宙中形成的恒星中元素是如何形成的问题。 例如，我们将能够执行第一次逼真的模拟流体动力学对流和核合成过程中的贫金属恒星，其中主机一个奇特的和鲜为人知的中间中子捕获过程。在异常的C增强贫金属s+r星中观测到了这种中间或i过程的丰度特征。它们是在大约十年前被发现的，它们是我们理解宇宙初期元素如何形成的关键。到目前为止，它们非常不寻常的丰度模式一直无法得到令人满意的解释。最近，我们发现了一个明显而吸引人的解决这个难题的方法。在贫金属的星星模型中，当富氢包层材料在更热、更深的对流不稳定层中对流混合时，就会遇到对流反应燃烧条件（类似于喷气发动机中的条件，除了用核燃烧而不是化学燃烧），其中有丰富的新鲜制造的12 C。在这样的条件下，可以实现公认的慢（s）和快（r）过程之间的中子密度。与我们的新的模拟能力，我们能够确定一个可能的网站，这i过程中的超级渐近巨星分支明星。我们进行了一些探索性的计算，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，以澄清这个问题的某些方面。 为了检验这一假设，我们将建立一个新的模拟能力交织的一维恒星演化与三维恒星流体动力学。在进一步的第二步，我们计划部署我们的经验，在大规模的后处理核合成模拟，以创建一个设施，可以确定在三维模拟表示的核合成。 虽然我们将继续使用我们现有的非常强大的仿真工具，例如NuGrid仿真代码，生成数据集，以便立即用于解释天文观测（例如通过银河系化学演化模型）我们建议为我们的计划提供足够的资金，以便创建新一代的模拟工具，使我们能够解决现有和未来的开放性问题观测数据