Benchmarking atomic data for astrophysics: Si III

G. Del Zanna, L. Fernandez Menchero, N.R. Badnell

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We investigate the main spectral diagnostics for Si iii UV lines, which have been previously used to measure electron densities, temperatures, and to suggest that non-Maxwellian electron distributions might be present in the low transition region of the solar atmosphere. Previous atomic calculations and observations are reviewed. We benchmark the observations using a new large-scale R-matrix scattering calculation for electron collisional excitation of Si iii, carried out with the intermediate-coupling frame transformation (ICFT) method. We find generally good agreement between predicted and observed line intensities, if one takes into account the different temperature sensitivity of the lines, and the structure of the solar transition region. We find no conclusive evidence for the presence of non-Maxwellian electron distributions.
Original languageEnglish
Article numberA99
Number of pages11
JournalAstronomy and Astrophysics
Early online date30 Jan 2015
Publication statusPublished - 1 Feb 2015


  • atomic data
  • spetroscopic techniques
  • corona
  • identification line

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