Atomic data for astrophysics: improved collision strengths for Fe VIII

G. Del Zanna, N.R. Badnell

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Abstract

We describe, and present the results of, a new large-scale R-matrix scattering calculation for the electron collisional excitation of Fe viii. We first discuss the limitations of the previous calculations, in particular concerning some strong EUV lines observed in the solar corona by the Hinode EUV Imaging Spectrometer. We then present a new target which represents an improvement over the previous ones for this particularly complex ion. We developed a new method, based on the use of term energy corrections within the intermediate coupling frame transformation method, to calculate the collision strengths. We compare predicted and observed line intensities using laboratory and solar spectra, finding excellent agreement for all the main soft X-ray and extreme ultraviolet (EUV) transitions, using the present atomic data. In particular, we show that Fe viii EUV lines observed by Hinode EIS can now be used to provide reliable electron temperatures for the solar corona.
Original languageEnglish
Article numberA56
Number of pages9
JournalAstronomy and Astrophysics
Volume570
Early online date16 Oct 2014
DOIs
Publication statusPublished - Oct 2014

Keywords

  • atomic data
  • Fe VIII
  • collision strengths
  • electron temperatures
  • sun flares

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