Journal Article

Emission lines of Fe <span class="smallCaps">xi</span> in the 257–407 Å wavelength region observed in solar spectra from EIS/<i>Hinode</i> and SERTS

F. P. Keenan, R. O. Milligan, D. B. Jess, K. M. Aggarwal, M. Mathioudakis, R. J. Thomas, J. W. Brosius and J. M. Davila

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 404, issue 3, pages 1617-1624
Published in print May 2010 | ISSN: 0035-8711
Published online May 2010 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2010.16389.x
Emission lines of Fe xi in the 257–407 Å wavelength region observed in solar spectra from EIS/Hinode and SERTS

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Theoretical emission-line ratios involving Fe xi transitions in the 257–407 Å wavelength range are derived using fully relativistic calculations of radiative rates and electron impact excitation cross-sections. These are subsequently compared with both long wavelength channel Extreme-Ultraviolet Imaging Spectrometer (EIS) spectra from the Hinode satellite (covering 245–291 Å) and first-order observations (∼235–449 Å) obtained by the Solar Extreme-ultraviolet Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and 276.36 Å lines of Fe xi are detected in two EIS spectra, confirming earlier identifications of these features, and 276.36 Å is found to provide an electron density (Ne) diagnostic when ratioed against the 257.55 Å transition. Agreement between theory and observation is found to be generally good for the SERTS data sets, with discrepancies normally being due to known line blends, while the 257.55 Å feature is detected for the first time in SERTS spectra. The most useful Fe xi electron density diagnostic is found to be the 308.54/352.67 intensity ratio, which varies by a factor of 8.4 between Ne= 108 and 1011 cm−3, while showing little temperature sensitivity. However, the 349.04/352.67 ratio potentially provides a superior diagnostic, as it involves lines which are closer in wavelength, and varies by a factor of 14.7 between Ne= 108 and 1011 cm−3. Unfortunately, the 349.04 Å line is relatively weak, and also blended with the second-order Fe x 174.52 Å feature, unless the first-order instrument response is enhanced.

Keywords: atomic data; Sun: activity; Sun: corona; Sun: UV radiation

Journal Article.  5663 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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