Cairo University

MTPR Journal

 

The Iron Project: RADIATIVE ATOMIC PROCESSES IN ASTROPHYSICS

& doi: https://doi.org/10.1142/9789814317511_0002
SULTANA N. NAHAR
Dept of Astronomy, The Ohio State University, Columbus, OH 43210, USA
Vol./Issue: 11 , id: 305

Astronomical objects, such as, stars, galaxies, blackhole environments, etc are studied through their spectra produced by various atomic processes in their plasmas. The positions, shifts, and strengths of the spectral lines provide information on physical processes with elements in all ionization states, and various diagnostics for temperature, density, distance, etc of these objects. With presence of a radiative source, such as a star, the astrophysical plasma is dominated by radiative atomic processes such as photoionization, electron-ion recombination, bound-bound transitions or photo-excitations and de-excitations. The relevant atomic parameters, such as photoionization cross sections, electron-ion recombination rate coefficients, oscillator strengths, radiative transition rates, rates for dielectronic satellite lines etc are needed to be highly accurate for precise diagnostics of physical conditions as well as accurate modeling, such as, for opacities of astrophysical plasmas. for opacities of astrophysical plasmas. This report illustrates detailed features of radiative atomic processes obtained from accurate ab initio methods of the latest developments in theoretical quantum mechanical calculations, especially under the international collaborations known as the Iron Project (IP) and the Opacity Project (OP). These projects aim in accurate study of radiative and collsional atomic processes of all astrophysically abundant atoms and ions, from hydrogen to nickel, and calculate stellar opacities and have resulted in a large number of atomic parameters for photoionization and radiative transition probabilities. The unified method, which is an extension of the OP and the IP, is a self-consistent treatment for the total electron-ion recombination and photoionization. It incorporates both the radiative and the dielectronic recombination processes and provides total recombination rates and level-specific recombination rates for hundreds of levels for a wide range of temperature of an ion. The recombination features are demonstrated. Calculations are carried out using the accurate and powerful R-matrix method in the close-coupling approximation. The relativistic fine structure effects are included in the Breit-Pauli approximation. The atomic data and opacities are available on-line from databases at CDS in France and at the Ohio Supercomputer Center in the USA. Some astrophysical applications of the results of the OP and IP from the Ohio State atomic-astrophysics group are also presented. These same studies, however with different elements, can be extended for bio-medical applications for treatments. This will also be explained with some preliminary findings.