EDP Sciences
Free Access
Volume 508, Number 1, December II 2009
Page(s) 513 - 524
Section Atomic, molecular, and nuclear data
DOI https://doi.org/10.1051/0004-6361/200912557
Published online 08 October 2009
A&A 508, 513-524 (2009)
DOI: 10.1051/0004-6361/200912557

Benchmarking atomic data for astrophysics: Fe VIII EUV lines

G. Del Zanna

DAMTP, Centre for Mathematical Sciences, Wilberforce road, Cambridge CB3 0WA, UK
    e-mail: GDelZanna@spd.aas.org

Received 22 May 2009 / Accepted 17 September 2009

The EUV spectrum of $\ion{Fe}{viii}$ is reviewed, using new solar observations from the Hinode EUV Imaging Spectrometer (EIS), together with older solar and laboratory data. The most up-to-date scattering calculations are benchmarked against these experimental data, with the use of a large atomic structure calculation. Once adjustments are made to the excitation rates, good agreement is found between calculated and observed line intensities. All previous line identifications have been re-assessed. Several lines are identified here for the first time, most notably the strong decays from the 3s2 3p5 3d2 4Dj levels. It is shown that they provide a new, important diagnostic of electron temperature for the upper transition region. The temperatures obtained at the base of solar coronal loops are lower (log T [K] = 5.5) than those predicted by assuming ionization equilibrium (log T [K] = 5.6), however firm measurements will only be possible once better scattering calculations are available, and the EIS radiometric calibration is properly assessed.

Key words: line: identification -- atomic data -- Sun: transition region -- techniques: spectroscopic

© ESO 2009