Emission UV de l’ion azote N2+ et son application au diagnostic en température électronique de la région de transition solaire

Abstract

We are interested in diagnostic of the electron temperature Te of the solar transition region which is a relatively thin area of the solar atmosphere located between the cool chromosphere and the hot corona. The temperature diagnostic is based on the intensity ratio R of the UV emission lines of the nitrogen ion N2+ at wavelengths 980 and 990 Å. We have performed detailed calculations of the ratio R as a function of Te in the range (4-16)104 K, using a collisional-radiative model in which the first 20 fine structure levels of the N2+ ion were taken into account. The atomic data needed in the calculations of the populations of the higher levels of the lines were obtained in part with FAC (Flexible Atomic Code). We have applied the results of our calculations of the R intensity ratio to deduce the temperature Te of the transition region from a UV spectrum of high spatial resolution recorded by the spectrometer SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on board of the satellite SOHO (SOlar and Heliospheric Observatory) which is located at about 1.5 millions of kilometers from the planet earth in direction of the sun.