Solving the Nebular Abundances Anomaly: New Features in Photoionization and Recombination

该项目旨在解决长期以来在光电离弥漫星云，特别是行星状星云中常见元素（如碳、氮、氧和氖）丰度的差异。光薄环境中的电离结构是由光电离和复合控制的。谱线形成的物理过程是电子冲击激发（EIE）或电子-离子复合（RC）和辐射衰减率。在由eee激发的发射谱线和同一原子种类的电子-离子复合谱线产生的谱线之间，发现了一个令人困惑的丰度差异，高达一个数量级以上。这不仅对光电离和重组的基本物理学提出了质疑，而且对气体星云中元素的物理结构和分布的解释也提出了质疑。本项目将研究前者，以解决后者。具体来说，计算将基于：i)电子-离子复合的统一理论，包括辐射和介电子复合过程，并为光电离、复合和激发过程提供了一套自一致的原子数据；（ii）最新的r矩阵方法的扩展，包括迄今未考虑的相对论效应；(3)对光电离和重组的初步计算，证明了低能共振的作用，这可能对解决丰度异常问题至关重要。该项目将涉及对许多元素的关键原子参数进行大规模和高精度的计算。高精度是必要的，因为天体物理模型需要排除原子物理作为任何重要的不确定性来源。重点将放在低电离阶段的一些最突出的元素上：碳、氮、氧、氖、镁、硅和硫。该项目将产生广泛和自一致的高精度辐射和碰撞原子参数集。通过分析它们的光学和红外光谱，天文学家试图了解弥漫的星际云或“星云”中氢被电离的元素的丰度。他们通过测量不同元素离子的特征发射强度来确定星云的物理性质，包括组成元素的丰度。这些发射线可以通过几个过程被激发，并且在使用碰撞激发的光谱线与由于电子捕获而测量的丰度之间存在长期的差异。该项目旨在通过计算原子参数的理论值来消除一个不确定性水平，这些参数与激发和发射强度有关。这项研究的结果将适用于天体物理学的许多子领域，从研究我们自己的星系到最遥远的类星体的丰度。

This project aims to resolve longstanding discrepancies in the abundances of common elements such as carbon, nitrogen, oxygen, and neon in photoionizaed diffuse nebulae, particularly planetary nebulae. The ionization structure in optically thin environments is governed by photoionization and recombination. The physical processes underlying spectral line formation are electron impact excitation (EIE) or electron-ion recombination (RC), and radiative decay rates. A perplexing discrepancy in abundances, of up to an order of magnitude of more, is found between those derived from emission lines excited due to EIE and those from electron-ion recombination lines of the same atomic species. This not only calls into question the basic physics of photoionization and recombination, but also the interpretation of the physical structure and distribution of elements within gaseous nebulae. This project will examine the former in order to address the latter. Specifically, calculations will be based on: i) the unified theory of electron-ion recombination that subsumes radiative and dielectronic recombination processes, and provides a self-consistent set of atomic data for photoionization, recombination and excitation processes, (ii) recent extensions in the state-of-the-art R-matrix method including relativistic effects not heretofore considered, and (iii) pilot calculations for photoionization and recombination demonstrating the role of low-energy resonances that may be crucial to resolving the abundance(s) anomaly problem. The project will involve large-scale and high-accuracy calculations of the critical atomic parameters for a number of elements. High precision is imperative since astrophysical models need to rule out atomic physics as any significant source of uncertainty. The focus will be on some of the most prominent elements in low ionization stages: carbon, nitrogen, oxygen, neon, magnesium, silicon and sulfur. The project will result in extensive and self-consistent sets of high-accuracy radiative and collisional atomic parameters.Through analysis of their optical and infrared spectra, astronomers attempt to understand the abundances of the elements in diffuse insterstellar clouds or "nebulae" in which hydrogen is ionized. They do this by measuring the strengths of the characteristic emission from ions of different elements and use these to determine the physical properties within the nebula including the abundances of the constituent elements. These emission lines can be excited via several processes and there is a long standing discrepancy between the abundances measured using spectral lines excited by collisions versus those due to electron capture. This project aims to remove one level of uncertainty by calculating the theoretical values for the atomic parameters that relate the excitation to the strengths of the emission. The results of this research will be applicable across a number of sub-fields within astrophysics ranging from studies of our own galaxy to abundances in the most distant quasars.