Benchmarking atomic data for astrophysics: Fe VII and other cool lines observed by Hinode EIS
DAMTP, Centre for Mathematical Sciences, Wilberforce road Cambridge CB3 0WA, UK e-mail: GDelZanna@spd.aas.org
Accepted: 11 September 2009
The EUV spectrum of is reviewed, using new rates for electron impact excitation, atomic structure calculations, and experimental data. In particular, solar observations of a sunspot loop spectrum obtained from the Hinode EUV Imaging Spectrometer (EIS) are used. Previous line identifications, mostly based on laboratory data, have been assessed. Large discrepancies between observed and predicted line intensities and wavelengths are found for the decays from the 3s2 3p5 3d3 configuration, which are strong EUV lines. We ascribe these discrepancies to incorrect line identifications. A number of new identifications are proposed. With these, very good agreement between theory and experimental data is found. A few transitions, in particular from the 3s2 3p6 3d 4s configuration, are observed for the first time, and are shown to provide a new important diagnostic for measuring the electron temperature in the solar transition region. The temperatures obtained at the base of solar coronal loops are found to be close to the temperature of maximum abundance in ionization equilibrium (K). The assessment of the lines was done in conjunction with an assessment of all the strongest cool lines observed with EIS. This spectrum is rich in transition region lines. Some new identifications are presented, in particular for . Most of the strongest transitions are identified, however a large number of lines still awaits firm identification.
Key words: atomic data / line: identification / Sun: transition region / techniques: spectroscopic
© ESO, 2009