A. K. Srivastava1,*, Jagdev Singh2, B. N.
Dwivedi1, S. Muneeer, T. Sakurai3, K.
Ichinmoto3
1 Department of Applied Physics, Institute of Technology,
Banaras Hindu University, Varanasi 221 005, India
2Indian Institute of Astrophysics, Bangalore 560 034,
India
3National Astronomical Observatory, Osawa, Mitaka, Tokyo, Japan
Abstract. We consider the first 27-level atomic model of Fe XIII (5.9 K < log Te < 6.4 K) to estimate its ground level populations, taking account of electron as well as proton collisional excitations and de-excitations, radiative cascades, radiative excitations and de-excitations. Radiative cascade is impor- tant but the effect of dilution factor is negligible at higher electron densities. The 3 P1 - 3 P0 and 3P2 -3 P1 transitions in the ground configuration 3s23p2 of Fe XIII result in two forbidden coronal emission lines in the infrared region, namely 10747 and 10798 Ao While the 5303 Aogreen line is formed in the 3s2 3p ground configuration of Fe XIV as a 2P3/2-2 P1/2 magnetic dipole transition. The line-widths of simultaneously observed Fe XIV green and Fe XIII infrared forbidden coronal emission lines can be a useful diagnostic tool to de- duce temperature and nonthermal velocity in the largescale coronal structures using intensity ratios of the lines as the temperature signature, instead of as- suming ion temperature to be equal to the electron temperature. Since the line intensity ratios IG5303 /II R10747 and IG5303 /II R10798 have very weak density de- pendence, they are ideal monitors of temperature mapping in the solar corona. The computed ratios will be compared with the recently obtained observations in our next paper.
Keywords: Sun : corona - Sun : infrared