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Title:
Extreme Ultraviolet Emission Lines of Fe XIII in Solar and Stellar Spectra
Authors:
Keenan, F. P.; Foster, V. J.; Drake, J. J.; Tayal, S. S.; Widing, K. G.
Publication:
Astrophysical Journal v.453, p.906 (ApJ Homepage)
Publication Date:
11/1995
Origin:
APJ; KNUDSEN
ApJ Keywords:
ATOMIC PROCESSES, SUN: FLARES, SUN: UV RADIATION, ULTRAVIOLET: STARS
DOI:
10.1086/176450
Bibliographic Code:
1995ApJ...453..906K

Abstract

Recent R-matrix calculations of electron impact excitation rates for Fe XIII are used to derive the theoretical electron density sensitive emission line ratios R1 = I(3s23p2 1D-3s3p3 1D)/I(3s23p2 3P2-3s3p3 3P2) = I(318.12 Å)/I(320.80 Å) and R2 = I(3s23p2 1D-3s3p3 1P)/I(3s22p2 3P2-3s3p3 3S) = 1(256.42 Å)/I(251.95 Å), which are found to be up to 70% different from earlier diagnostics. A comparison of the current line ratios with both solar flare and active region observations, obtained by the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals generally good agreement between densities deduced from Fe XIII and those estimated from diagnostic line ratios in species formed at similar temperatures, such as I(219.12 Å)/I(211.32 Å) in Fe XIV. This provides experimental support for the accuracy of the line ratio calculations, and hence the atomic data adopted in their derivation. In Extreme Ultraviolet Explorer satellite (EUVE) spectra the Fe XIII emission lines are found to be severely blended. However, an analysis of these lines measured in the spectra of Procyon and α Cen demonstrates that they still allow very approximate values of the electron density to be inferred. Moreover, it should be possible to increase the accuracy of the measured line fluxes, and hence of the inferred densities, if longer exposures of the stars concerned can be obtained.

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