High-Precision Computational Spectroscopy Of Fe-Peak Elements

AST 0205827 Pradhan铁和铁峰元素的光谱是天文学的基本兴趣。尽管这些元素是超新星中恒星生命周期的最终产物，但它们可以追溯宇宙的化学和物理历史，甚至可以追溯到高红移（z）。特别是铁在大多数天文学来源中无处不在：恒星，活动星系核（AGN），超新星遗迹（SNR），以及星际和星系间介质（ISM和IGM）。一些基本的问题是：我们如何准确地分析光谱和确定各种类型的恒星的丰度？铁的丰度是恒星形成最早期的“计时器”吗？非峰元素的光谱能否作为“标准烛光”用于超新星的光谱校准？铁峰元素的光谱比较复杂。新一代望远镜和仪器的相当大的努力将指向高分辨率光谱学。但是观测的高分辨率在理论上要求高精度。由于基本原子参数的缺乏或缺乏，花费巨大努力和费用获得的光谱仍然没有得到充分的分析。铁和铁族元素尤其如此。然而，高精度的大规模计算是困难的，并且非常耗时。尽管在过去的十年中取得了进展，必要的精度和数量的原子参数的铁峰元素尚未达到使足够准确的numericalmodel。最近的进展主要归功于两个主要的国际原子天体物理学项目--不透明度项目和铁项目。虽然大多数最先进的理论工具都是在这些项目下开发的，但实际的计算还有待进行，需要进一步的发展。俄亥俄州州立大学的Anil Pradhan博士和同事们将根据铁和铁峰元素原子过程的相对论计算的最新进展进行全面的努力。这些主要涉及电子碰撞激发，光电离，复合和辐射跃迁概率。 Pradhan博士的努力是针对一些悬而未决的问题，需要数值光谱：（I）活动星系核和强Fe Ⅱ类星体的铁谱，（II）Fe峰元素（III）SNR中的Fe-Co-Ni光谱，（IV）用于恒星建模和丰度测定的非LTE单色不透明度，（V）非LTE模型中辐射传输的精确处理，（VI）研究活动星系核中的铁谱，Fe Ⅱ/Mg Ⅱ比值与红移的关系，以及SNR和星系中Fe Ⅱ/Ni Ⅱ丰度异常。物理激发机制，如莱曼α和紫外荧光将进行研究。目标原子处于低电离状态，主要在地面观测站的光学和近红外波段观测到。由于大量的计算资源是这项工作的先决条件，Pradhan博士在俄亥俄州哥伦布市的俄亥俄州超级计算机中心获得了大量的计算时间分配。

AST 0205827PradhanThe spectra of iron and iron-peak elements are of fundamental interest in astronomy. Althoughproduced as the end-products of stellar life cycles in supernovae, these elements trace the chemicaland physical history of the Universe even to high redshifts (z). Iron in particular is ubiquitous inmost astronomical sources: stars, active galactic nuclei (AGN), supernova remnants (SNR's), andthe interstellar and intergalactic media (ISM and IGM). Some of the basic questions are: Howaccurately can we analyze the spectra and determine abundances in various types of stars? Is theabundance of iron a `chronometer' of the earliest epochs of stellar formation? Can the spectra ofiron-peak elements be used for spectroscopic calibration of supernovae as `standard candles'?The spectra of iron-peak elements are complicated. A considerable effort by the new generation oftelescopes and instruments will be directed towards their high-resolution spectroscopy. But high resolution in observations demands high precision in theory. Spectra obtained with great effort and expense remain inadequately analyzed owing to the absence or paucity of fundamental atomic parameters. This is especially true of iron and iron-group elements. However, large-scale computations with high precision are difficult and very time consuming. Inspite of the progress made in the past decade, the requisite precision and quantity of the atomicparameters for iron-peak elements has not been attained to enable sufficiently accurate numericalmodels. Much of the progress in the recent past has been due to two major international projectsin atomic astrophysics - the Opacity Project and the Iron Project. While most of the state-of-the-art theoretical tools were developed under these projects, the actual computations are yet to be carried out and require further developments.Dr. Anil Pradhan and colleagues at the Ohio State University will carry out a comprehensive effort based on recent advances in relativistic calculations for atomic processes for iron and iron-peak elements. These relate primarily to electron impact excitation, photoionization, recombination, and radiative transition probabilities. Dr. Pradhan's effort is aimed at some outstanding problems that entail numerical spectroscopy of: (I) iron spectra from AGN and strong Fe II emitting quasars, (II) Fe-peak elements (Cr, Mn, Fe, Zn) in the IGM, (III) Fe-Co-Ni spectra in SNR's, (IV) Non-LTE monochromatic opacities for stellar modeling and abundance determinations, (V) an exact treatment of radiative transfer in Non-LTE models, using the new atomic data, for important ions such as Fe I-IV and Ni II, and (VI) for studies of iron spectra in AGN, Fe II/Mg II ratio vs. redshift, and Fe II/Ni II abundance anomalies in SNR's and galaxies. Physical excitation mechanisms such as Lyman-alpha and UV fluorescence will be studied. The targeted atomic species are in low-ionization statesobserved mainly in the Optical and Near-IR from ground-based observatories. As massive computational resources are an a priori requirement for this undertaking, Dr. Pradhan has secured a large allocation of computation time at the Ohio Supercomputer Center in Columbus, Ohio.***.