Spectroscopic Studies of the Solar Corona III. Density Diagnostics Using the Infrared Lines of Fe XIII

Abstract

We have obtained spectrographic observations of several coronal regions in three emission lines (6374Å [Fe X ], 10747Å [Fe XIII ], and 10798Å [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 10747Å and 10798Å 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 x 10/sup9/-2.4x10/sup8/ cm/sup-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 × 10/sup6/K and 8.3 × 10/sup6/K with a most frequent value around 1.8 × 10/sup6/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.