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3-D Simulations of i-Process Nucleosynthesis in the Early Universe

早期宇宙中 i-Process 核合成的 3-D 模拟

基本信息

批准号：
1440025
负责人：
Paul Woodward
金额：
$ 1.54万
依托单位：
University of Minnesota-Twin Cities
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2014
资助国家：
美国
起止时间：
2014-09-01 至 2015-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1440025&HistoricalAwards=false
关键词：
Simulations Process Nucleosynthesis Early Universe

项目摘要

Astronomical observations are now probing the early stages of the universe, in which galaxiesdeveloped and merged, and the formation of the structures in the universe at the present erawas set in motion. An important part of this story is the chemical evolution of galaxies. Theformation of the elements in the first stars and their subsequent dispersal are powerful tracersof structure formation and evolution in the early universe. This project involves the simulationof processes deep inside stars of the early universe that experience hydrogen ingestionevents caused by mixing of material across the boundaries of convection zones. In 1-D stellarevolution simulations, these give rise to rapid hydrogen burning, with enormous energy releaseand causing nucleosynthesis by neutron capture from neutron fluxes intermediate between theslow (s) and rapid (r) processes. This is the intermediate, or i-process nucleosynthesis thatis targeted in this study. Accurate treatment of the convective boundary mixing that drivesthis i-process requires full 3-D simulation. The rapid hydrogen burning that ensues, togetherwith the very large luminosities involved make 3-D simulation affordable on NSF?s powerfulnew supercomputing platform, Blue Waters, at NCSA.A new and powerful capability will be built in this project to simulate these events by couplingtogether 3-D simulations that cover brief time intervals with 1-D simulations spanning muchlonger times. In some cases that will be addressed, it is possible to simulate the entire eventin 3-D. In others, 3-D simulations performed at intervals as part of a coupled 1-D and 3-Dstellar evolution calculation will serve to recalibrate the coefficients in approximate 1-D modelsfor dynamic mixing processes. Such coupled calculations will use these periodic modelrecalibrations to validate the use of the models as the calculation progresses. When unacceptablylarge revisions of model "constants" are indicated, a recomputation with 3-D recalibrationstaken at shorter time intervals will result. This new process is called autocorrecting modeling.It involves periodic generation of large amounts of 3-D data from simulation codes. This datageneration is followed by a detailed analysis of the data in terms of 1-D models. The resultsof this analysis are then fed back into the 1-D stellar evolution computation. Pioneering thisnew approach is a major challenge of the project; the database of condensed simulation resultsthat will be built in the process will be a significant outcome of the project. This data will bemade available first to collaborators and ultimately to the broad community. It will be possibleto use this data to formulate, validate, and refine simplified models of the convective boundarymixing processes that are a major focus of this study. It will also be possible for others,potentially using quite different simulation software, to use this data to adopt an autocorrectingmodeling approach in studies of related problems. In the first year of this project, a continuationof present work with the well observed case of Sakurai's object is planned along with applicationof the new techniques to simulations of low-mass, low-metallicity AGB stars.

天文观测现在正在探索宇宙的早期阶段，在这个阶段，星系发展和合并，宇宙结构的形成在当前时代开始运动。这个故事的一个重要部分是星系的化学演化。第一批恒星中元素的形成和随后的扩散是早期宇宙结构形成和演化的强有力的踪迹。这个项目涉及模拟早期宇宙中恒星深处的过程，这些过程经历了由物质混合越过对流区边界引起的吸氢事件。在一维恒星旋转模拟中，它们引起快速的氢燃烧，释放出巨大的能量，并通过从流(S)和快(R)过程之间的中子流中俘获中子而引起核合成。这就是本研究的目标--中间体或I-过程核合成。精确处理驱动I过程的对流边界混合需要全三维模拟。随之而来的快速氢气燃烧，以及涉及的非常大的亮度，使得3-D模拟可以在国家科学基金会强大的新超级计算平台--国家科学院蓝水上进行。该项目将建立一个新的强大的能力来模拟这些事件，将覆盖短时间间隔的3-D模拟与跨越更长时间的1-D模拟结合在一起。在将被解决的某些情况下，有可能在3-D中模拟整个事件。在另一些情况下，作为耦合的一维和三维恒星演化计算的一部分，每隔一段时间进行的三维模拟将用于重新校准动态混合过程的近似一维模型中的系数。随着计算的进行，这种耦合计算将使用这些周期性的模型重新校准来验证模型的使用。当指出对模型“常数”进行不可接受的大修改时，将导致以较短的时间间隔进行三维重新校准的重新计算。这一新的过程被称为自动校正建模，它涉及从仿真代码定期生成大量三维数据。在此数据生成之后，根据一维模型对数据进行了详细分析。然后，这种分析的结果被反馈到一维恒星演化计算中。开创这一新方法是该项目的一个主要挑战；在此过程中将建立的浓缩模拟结果数据库将是该项目的一个重要成果。这些数据将首先提供给合作者，最终提供给广大社区。这将有可能利用这些数据来制定、验证和改进对流边界混合过程的简化模式，这是本研究的主要重点。其他人，可能使用完全不同的模拟软件，也可能使用这些数据在相关问题的研究中采用自动校正建模方法。在这个项目的第一年，计划继续目前的工作，以樱井天体为例，并将新技术应用于模拟低质量、低金属丰度的AGB恒星。