Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-07-10
Astronomy and Astrophysics
Astrophysics
15 pgs., 5 color figs., Invited Review, Proceedings of the Workshop on Stellar Atmosphere Modeling, Tuebingen, Germany, April
Scientific paper
Latest developments in theoretical computations since the international Opacity Project (OP), under the new the Iron Project (IP) and extensions, are described for applications to a variety of objects such as stellar atmospheres, nebulae, and active galactic nuclei. The primary atomic processes are: electron impact excitation (EIE), photoionization, electron-ion recombination, and bound-bound transitions, all considered using the accurate and powerful R-matrix method including relativistic effects. As an extension of the OP and the IP, a self-consistent and unified theoretical treatment of photoionization and recombination has been developed. Both the radiative and the dielectronic recombination (RR and DR) processes are considered in a unified manner. Photoionization and recombination cross sections are computed with identical wavefunction expansions, thus ensuring self-consistency in an ab initio manner. The new unified results differ from the sum of previous results for RR and DR by up to a factor of 4 for the important but complex atomic systems such as Fe I - V. The fundamental differences are due to quantum mechanical intereference and coupling effects neglected in simpler approximations that unphysically treat RR and DR separately, which can not be independently measured or observed. I will also describe the electronic, web-interactive, database, TIPTOPBASE, to archive the OP/IP data in a readily accessible manner. TIPTOPBASE would also include electron-ion recombination data and new fine structure transition probabilities. Efficient codes developed by M.J. Seaton to calculate `customized' mixture opacities and radiative accelerations ('levitation') in stars will also be available.
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