AAS 206th Meeting, 29 May - 2 June 2005
Session 31 Highlights in Laboratory Astrophysics
Topical Session, Wednesday, 8:30-10:00am, 10:45am-12:30pm, 2:30-4:00pm, 4:15-6:00pm, June 1, 2005, 102 D

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[31.23] Dielectronic Recombination, Photoionization and Opacities

N. R. Badnell (University of Strathclyde, UK)

As first noted by Alan Burgess, dielectronic recombination (DR) is the dominant electron-ion recombination process in many astrophysical and laboratory plasmas. DR rate coefficients are needed for determining both the level populations and the ionization balance of plasmas over a wide range of electron densities and plasma timescales. Accurate DR rate coefficients are essential for the reliable spectral diagnosis of non-equilibrium laboratory and astrophysical plasmas.

The rapid advancement of X-ray satellite resolving power (Chandra, XMM-Newton) places new demands on the theoretical modelling of photoionized plasmas. Here the ionization balance occurs at much lower temperatures, for the same ion, compared to electron collision dominated plasmas. In particular, DR through non-dipole core excitations becomes important, viz. between terms of the ground configuration and between levels of the ground term.

In an effort to provide a comprehensive upgrade to the DR database available, over and above the familiar Burgess General Formula for example, we have embarked on a programme for the generation of a DR database which would meet modern demands. We will review methodologies for describing DR and look briefly at the state-of-play of theory vs experiment. We then discuss how to deliver DR data in a form suitable for modelling and we review the status of our partial and total DR database being assembled for the modelling of photoionized and/or dynamic finite-density plasmas.

We also consider the inverse process of photoionization and discuss how the same approach to DR is being used for inner-shell photoionization and the determination of opacities in stellar interiors. In particular, we pay attention to the role of opacity in resolving the discrepancy between the helioseismology observations and stellar evolution models for the position of the base of the solar convective zone.

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