High-Precision Computational Spectroscopy Of Fe-Peak Elements

铁和铁峰元素的光谱在天文学中具有重要意义。虽然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)。铁尤其普遍存在于大多数天文来源中：恒星、活动星系核(AGN)、超新星遗迹(SNR‘s)以及星际和星际介质(ISM和IGM)。一些基本的问题是：我们如何准确地分析光谱并确定不同类型恒星的丰度？铁的丰度是恒星形成最早时期的“天文计时器”吗？非峰元素的光谱是否可以作为“标准蜡烛”用于超新星的光谱定标？铁峰元素的光谱很复杂。新一代望远镜和仪器的相当大的努力将指向它们的高分辨率光谱学。但高分辨率的观测在理论上要求有很高的精度。由于缺乏或缺乏基本原子参数，花费大量精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和非常耗时的。尽管在过去十年中取得了进展，但铁峰元素的原子参数还没有达到足够精确的数值模型所需的精度和数量。最近取得的许多进展归功于原子天体物理领域的两个重大国际项目--不透明项目和铁项目。虽然大多数最先进的理论工具都是在这些项目下开发的，但实际计算仍有待进行，需要进一步发展。俄亥俄州立大学的阿尼尔·普拉丹和他的同事们将基于铁和铁峰元素原子过程的相对论计算的最新进展，开展一项全面的努力。这些主要与电子碰撞激发、光致电离、复合和辐射跃迁几率有关。Pradhan博士的努力针对的是一些突出的问题，这些问题需要数值光谱分析：(I)来自活动星系核和发射强FeII的类星体的铁谱，(Ii)IGM中的铁峰元素(Cr，Mn，Fe，Zn)，(Iii)SNR中的Fe-Co-Ni谱，(Iv)用于恒星模型和丰度测定的非LTE单色不透明度，(V)使用新的原子数据精确处理非LTE模型中的辐射传递，用于重要离子，如Fe I-IV和Ni II，以及(Vi)用于研究AGN中的铁谱，信噪比和星系中Fe II/Mg II比值与红移的关系，以及Fe II/Ni II丰度异常。物理激发机制，如莱曼-阿尔法和紫外光荧光将被研究。目标原子物种处于低电离态，主要在地面观测站的光学和近红外光谱中观察到。由于大量的计算资源是这项工作的先天要求，普拉丹博士已经在俄亥俄州哥伦布市的俄亥俄超级计算机中心获得了大量计算时间的分配。

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.***.