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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611826
• 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。