Journal Article

Extreme ultraviolet emission lines of Ar <span class="smallCaps">xiv</span> in solar active region and flare spectra

F. P. Keenan, A. C. Katsiyannis, R. H. G. Reid, A. K. Pradhan, H. L. Zhang and K. G. Widing

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 346, issue 1, pages 58-62
Published in print November 2003 | ISSN: 0035-8711
Published online November 2003 | e-ISSN: 1365-2966 | DOI:
Extreme ultraviolet emission lines of Ar xiv in solar active region and flare spectra

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New R-matrix calculations of electron impact excitation rates for transitions among the 2s22p, 2s2p2 and 2p3 levels of Ar xiv are presented. These data are subsequently used to derive the theoretical electron density diagnostic emission-line intensity ratios R1=I(187.95 Å)/I(194.41 Å) and R2=I(257.40 Å)/I(243.78 Å) for a range of densities (Ne= 109–1013 cm−3) and electron temperatures (Te= 106.3–106.7 K) appropriate to solar transition region and coronal plasmas. A comparison of these diagnostics with observational data for solar active regions and flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals that the electron densities determined from R1 are in good agreement with those estimated from line ratios in Fe xiv or Fe xv, which are formed at similar electron temperatures to Ar xiv. However, there are large discrepancies between densities inferred from the R2 ratio and those from Fe xiv or Fe xv, confirming that the Ar xiv 243.78- and 257.40- Å lines are badly blended with Fe xv 243.79 Å and Fe xiv 257.38 Å, respectively. Hence, R2 cannot be employed as a density diagnostic, in contrast to R1, which does provide reliable Ne estimates.

Keywords: atomic data; Sun: activity; Sun: flares; ultraviolet: general

Journal Article.  2124 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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