Excitation of the Fe XIII Spectrum in the Solar Corona
Abstract
Summary. The statistical equilibrium equations of the 3P0,1,2, `D2 and 15o levels of the ground 3p2 configuration of Fe +12 have been solved for the ranges of electron temperature, electron density and geometrical dilution factor believed to be relevant to Fe xiii emission from the solar corona. Direct collisional and radiative transitions between these levels and indirect collisional excitation of allowed transitions to the 3s 3p3 and 3p 3d configurations followed by radiative decay to the ground configuration are taken into account using new atomic data calculated in intermediate coupling allowing for the effects of configuration interaction. Particular attention is paid to assessing the remaining uncertainties in the atomic parameters. The indirect process is found to be the dominant collisional process in the statistical equilibrium equations. The variation of the t0747/ 10798 and 3388/ 10747 line intensity ratios are presented as functions of electron density and consistent values of the electron density of the emitting region are obtained when the calculated intensity ratios are combined with existing observations. Key words: solar corona  silicon isoelectronic sequence  statistical equilibrium equations
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 1973
 Bibcode:
 1973A&A....24..181F