High-Precision Computational Spectroscopy Of Fe-Peak Elements

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

AST 0205827 Pradhan The spectra of iron and iron-peak elements are of fundamental interest in astronomy. Although produced as the end-products of stellar life cycles in supernovae, these elements trace the chemical and physical history of the Universe even to high redshifts (z). Iron in particular is ubiquitous in most astronomical sources: stars, active galactic nuclei (AGN), supernova remnants (SNR's), and the interstellar and intergalactic media (ISM and IGM). Some of the basic questions are: How accurately can we analyze the spectra and determine abundances in various types of stars? Is the abundance of iron a `chronometer' of the earliest epochs of stellar formation? Can the spectra of iron-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 of telescopes 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. In spite of the progress made in the past decade, the requisite precision and quantity of the atomic parameters for iron-peak elements has not been attained to enable sufficiently accurate numerical models. Much of the progress in the recent past has been due to two major international projects in 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 states observed 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. *** .