Extreme ultraviolet transitions of Fe XXI in solar, stellar and laboratory spectra

Francis Keenan, Kanti Aggarwal, Michail Mathioudakis, D.R. Williams, K.J.H. Phillips

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


Recent R-matrix calculations of electron impact excitation rates for transitions among the 2s(2)2p(2), 2s2p(3) and 2p(4) levels of Fe XXI are used to derive theoretical electron density (N-e) sensitive emission-line ratios involving 2S2(2)p(2)-2s2p(3) transitions in the similar to 98-146 Angstrom wavelength range. A comparison of these with observations from the PLT tokamak plasma, for which the electron density has been independently determined, reveals generally very good agreement between theory and experiment, and in some instances removes discrepancies found previously. The observed Fe XXI ratios for a solar flare, obtained with the OSO-5 satellite, imply electron densities which are consistent, with discrepancies that do not exceed 0.2 dex. In addition, the derived values of N-e are similar to those estimated for the high-temperature regions of other solar flares. The good agreement between theory and observation, in particular for the tokamak spectra, provides experimental support for the accuracy of the present line-ratio calculations, and hence for the atomic data on which they are based.
Original languageEnglish
Pages (from-to)1387-1390
Number of pages4
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 01 Oct 2001

ASJC Scopus subject areas

  • Space and Planetary Science


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