Diagnostic en densité des régions actives solaires basé sur les raies d’émission EUV de l’ion Fe12+

Abstract

The emission lines of the iron ion Fe12+ in the range of extreme ultraviolet are frequently used in spectroscopic diagnostics of hot plasmas of the universe in order to determine the electron density Ne. We have studied the variations of the emissivity ratio of the lines corresponding to the transitions 3s23p3d 3P1  3s23p2 3P0 at 202.0 Å and 3s23p3d 3D2,3  3s23p2 3P2 at 203.8 Å as a function of Ne going from 108 to 1011 cm3. For this, we have evaluated the populations of the higher levels of these lines by employing a model which takes into account of the processes of collisional excitations and de-excitations as well as spontaneous radiative decays between the first 27 fine structure levels of Fe12+ ion. The computer code ‘‘Flexible Atomic Code’’ was run to obtain all the atomic data required in the calculations of the R ratio. The results of our R calculations have been applied to deduce the Ne density of solar active regions from high resolution spectra observed with spectrometers on board rocket and satellite.