Atomic data for the astrophysics: Fe XII soft X-ray lines.

G. Del Zanna, P. J. Storey, N. R. Badnell, H.E. Mason

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Abstract

We present new large-scale R-matrix (up to n = 4) and distorted-wave (DW, up to n = 6) scattering calculations for electron collisional excitation of Fe xii. The first aim is to provide accurate atomic data for the soft X-rays, where strong decays from the n = 4 levels are present. As found in previous work on Fe x, resonances attached to n = 4 levels increase the cross-sections for excitations from the ground state to some n = 4 levels, when compared to DW calculations. Cascading from higher levels is also important. We provide a number of models and line intensities, and list a number of strong unidentified lines. The second aim is to assess the effects of the large R-matrix calculation on the n = 3 transitions. Compared to our previous (n = 3) R-matrix calculation, we find overall excellent agreement to within a few percent, however a few key density diagnostic EUV intensities differ by about 60% at coronal densities. The new atomic data result in lower electron densities, resolving previous discrepancies with solar observations.
Original languageEnglish
Article numberA139
Number of pages10
JournalAstronomy and Astrophysics
Volume543
DOIs
Publication statusPublished - 12 Jul 2012

Keywords

  • atomic data
  • identification line
  • spectroscopic techniques
  • sun
  • corona
  • Fe xii
  • electron collisional excitation
  • coronal densities
  • extreme ultraviolet lines

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