Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.......118b&link_type=abstract
Thesis (PhD). QUEEN'S UNIVERSITY OF BELFAST (NORTHERN IRELAND), Source DAI-C 60/01, p. 144, Spring 1999, 162 pages.
Astronomy and Astrophysics
Astrophysics
Scientific paper
The relevance of iron in astrophysics is explained using the iron K/alpha line as example. Results are presented from 11-target and 31-target R- matrix calculations of Fe XXIV and Fe XXIII 1s photoejection respectively. These are seen to be within a few % of the best existing (relativistic) data. However, no resonance structure is evident in the old data and the new data displays a large amount of resonance structure, up to several orders of magnitude greater than background in cases. The excellent agreement with existing relativistic data suggests that, as has been concluded elsewhere, relativisitic effects may be neglected in a sufficiently complex LS coupling calculation for high Z ions. Results are also presented of a 9-target R-matrix calculation on the 1s photoejection of Fe I. The resulting cross-section is seen to be a different shape and up to 41% higher than the best existing data. Simple rates calculations suggest that there will be a marked difference in modelling calculations (up to about 20% in cases) using these more accurate cross-sections presented. The Fe I calculation was complex because of the large energy gap between the initial Fe I ground state and the final '1s hole' Fe II target states. Although it made the calculation more complex, the Fe II ground state was excluded from the wavefunction expansion to make it more physically accurate. It was thought the calculation would progress anyway as long as the (N + 1) electron terms dominated the close-coupling wavefunction expansion. This was seen to be true, and it was thus shown that the R- matrix codes could be applied successfully to calculations of deep inner-shell phenomena, without the inclusion of intermediate states in the wavefunction expansion (such as the Fe II ground state). This is the first proof that the R-matrix codes may be applied to such phenomena, and in such a novel way.
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