Theory of Recombination Lines in Astrophysical Sources

天体物理源中的复合线理论

• 批准号: 0506889
• 负责人: Anil Pradhan
• 金额: $ 29.4万
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-07-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0506889&HistoricalAwards=false
• 关键词: Theory; Recombination; Lines; Astrophysical; Sources

AST-0506889PradhanDetermination of accurate element abundances is a fundamental problem in astrophysics. But abundance anomalies and inaccuracies abound in individual and entire classes of sources. Galactic and extragalactic H II regions are among the most extensively observed objects; yet, abundances from different methods are discrepant by several factors or even orders of magnitude, such as the large variations in the iron/nickel ratio deduced from emission line studies. Dr. Anil Pradhan's effort with this award will enable accurate determination of physical conditions and element abundances derived from emission lines by (A) the first calculations of recombination line intensities for a number of astrophysically abundant ions, and (B) including the heretofore neglected contribution of electron-ion recombination to prominent emission lines. The main theoretical issue (as opposed to observational uncertainties) is that accurate analysis of observed lines from abundant atomic ions depend on atomic parameters that are highly uncertain. The two primary mechanismsare collisional excitation and electron-ion recombination. A longstanding problem in astrophysics is the continuing discrepancy between abundances derived using these two methods. Whereas considerable theoretical work has been done on the calculation of collisional excitation cross sections and rate coefficients, little effort has been devoted to the theory of recombination lines except for hydrogen-like, helium-like and a few other light ions. This is due to the inherent difficulty in the treatment of the atomic physics of a large number of levels that contribute to the formation of recombination lines. Abundance inhomogeneities may also be related to structure and physical processes. Very detailed optical and near-infrared (O/NIR) spectra already exist, and will undergo a huge increase in quality and quantity with the advent of new 8-m class telescopes and high-resolution spectrographs. In principle, therefore, spectral studies should be able to ascertain element abundances precisely. Dr. Pradhan's work will help rule out uncertainties due to atomic data and neglected atomic processes. He will utilize recent extensions of the most advanced atomic physics techniques, developed under the Opacity Project and the ongoing Iron Project, using the powerful and state-of-the-art relativistic R-matrix method, and a new method for calculating total and level-specific recombination rate coefficients subsuming both the radiative and the dielectronic recombination processes. Detailed treatments of relativistic fine structure and resonance phenomena are essential for accuracy, and would be incorporated in an ab initio manner. The primary emphasis will be on some of the most important elements C,N,O,Ne,Si,S, Fe, and Ni in multiple ionization states.Several areas of physics and astrophysics should benefit from the study of radiative processes and data in the proposed research. Very accurate and large sets of transition probabilities will be calculated for use in the construction of recombination-cascade matrices that yield the effective rate coefficients. In addition, Dr. Pradhan's theoretical approach is based on a self-consistent treatment of photoionization and recombination in an ab initio quantum mechanical manner. A wide range of applications to laboratory and astrophysical plasma sources are envisaged. The results of this work should be broadly applicable to the understanding of elemental composition of stars, nebulae and HII regions, galaxies, supernovae, etc., and hence the chemical history of the Universe. This project is especially designed for training of graduate students as the next generation of astrophysicists capable of these complex calculations. The project relies heavily on high-performance computing. The computational tools and resources needed for this undertaking have been secured on a variety of vector and massively parallel platforms through a Special Allocation at the Ohio Supercomputer Center at no cost to NSF.***

准确测定元素丰度是天体物理学中的一个基本问题。但是丰度异常和不准确性在个别和整个源类中比比皆是。银河系和河外H II区是最广泛观测的天体之一;然而，不同方法的丰度有几个因素甚至几个数量级的差异，例如从发射线研究中推导出的铁/镍比的变化很大。 Anil Pradhan博士获得该奖项的努力将能够准确地确定物理条件和元素丰度，这些元素来自于（A）对许多天体物理丰富的离子的复合线强度的首次计算，以及（B）包括迄今为止被忽视的电子-离子复合对突出发射线的贡献。主要的理论问题（相对于观测的不确定性）是，对大量原子离子的观测谱线的准确分析取决于高度不确定的原子参数。两个主要机制是碰撞激发和电子-离子复合。天体物理学中一个长期存在的问题是使用这两种方法得出的丰度之间的持续差异。尽管在碰撞激发截面和速率系数的计算方面已经做了大量的理论工作，但除了类氢、类氦和少数其他轻离子外，很少有人致力于复合线的理论。这是由于在处理的原子物理学的大量的水平，有助于复合线的形成固有的困难。 绝对不均匀性也可能与结构和物理过程有关。非常详细的光学和近红外光谱已经存在，并且随着新的8米级望远镜和高分辨率摄谱仪的出现，质量和数量都将大幅增加。因此，原则上，光谱研究应该能够精确地确定元素丰度。 Pradhan博士的工作将有助于排除由于原子数据和被忽视的原子过程造成的不确定性。 他将利用最先进的原子物理技术的最新扩展，在不透明度项目和正在进行的铁项目下开发，使用强大的和最先进的相对论R矩阵方法，以及一种新的方法来计算总的和特定水平的复合速率系数，包括辐射和双电子复合过程。相对论精细结构和共振现象的详细处理是必不可少的准确性，并将纳入从头算的方式。主要的重点将放在一些最重要的元素C，N，O，Ne，Si，S，Fe和Ni的多电离态。物理学和天体物理学的几个领域应该受益于辐射过程的研究和数据在拟议的研究。将计算非常精确和大量的转移概率，用于构建产生有效速率系数的重组级联矩阵。此外，Pradhan博士的理论方法是基于从头算量子力学方式的光电离和复合的自洽处理。 广泛的应用，实验室和天体物理等离子体源的设想。这项工作的结果应广泛适用于了解恒星、星云和HII区、星系、超新星等的元素组成，也就是宇宙的化学史该项目是专门为培养研究生而设计的，他们将成为能够进行这些复杂计算的下一代天体物理学家。该项目在很大程度上依赖于高性能计算。这项工作所需的计算工具和资源已通过俄亥俄州超级计算机中心的特别分配在各种矢量和大规模并行平台上得到保障，NSF不承担任何费用。*