Abstract
Recent R-matrix calculations of electron impact excitation rates in Fe xii are used to derive the theoretical emission line ratio R 1 = I(195.1 Å)/I(1242 Å), which is potentially a useful electron density diagnostic for the solar inner corona (r ≤ 1.05 61-01). These results are found to be significantly different from the earlier estimates of Withbroe and Raymond (1984), but are in good agreement with the observed values of R 1, for the quiet Sun and an active region. Adoption of the R-matrix atomic data for the 1242 Å line in the coronal iron abundance determination removes an existing discrepancy between results derived from the EUV transition and other iron lines in the solar XUV spectrum. The R-matrix calculations confirm the prediction of Withbroe and Raymond that the earlier discrepancies in R 1 and the iron abundance were due to the 1242 Å line excitation rates being underestimated by a factor of ~2. Withbroe and Raymond's paper is, therefore, an excellent example of how astronomical observations can be used to accurately predict atomic physics data.
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Keenan, F.P., Tayal, S.S. & Henry, R.J.W. The Fe xii 195.1 Å/1242 Å emission line ratio in the solar corona. Sol Phys 125, 61–65 (1990). https://doi.org/10.1007/BF00154779
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DOI: https://doi.org/10.1007/BF00154779