Spectroscopic Studies of the Solar Corona III. Density Diagnostics Using the Infrared Lines of Fe <scp>xiii</scp>

Abstract

Abstract We have obtained spectrographic observations of several coronal regions in three emission lines (6374 Å [Fe x ], 10747 Å [Fe xiii], and 10798 Å [Fe xiii]) simultaneously. The 25-cm coronagraph at Norikura Observatory and two large-format CCD cameras were used. The peak intensity, velocity, and line-width values were derived from Gaussian fits to the observed line profile at each location of the observed region. The ratio of the intensities of the 10747 Å and 10798 Å emission lines in the individual coronal structures range between 1.0 and 2.5 at $ 10''$ above the limb, which corresponds to a density range of $ 9.8 \times 10^9 \hbox{--} 2.4 \times 10^8 \,\mathrm{cm}^{-3}$. The scale-height temperature values, derived from the variations of the intensity ratio with height above the limb for all individual coronal structures, range between $ 0.6 \times 10^ 6 \,\mathrm{K}$ and $ 8.3 \times 10^6 \,\mathrm{K}$ with a most frequent value around $ 1.8 \times 10^6 \,\mathrm{K}$. The large values of the scale-height temperature for 70% of the structures indicate that these structures may not be in hydrostatic equilibrium nor be isothermal in nature.