Jagdev Singh1*, S. Muneer1, Takashi
Sakurai2 and Kiyoshi Ichimoto2
1Indian Institute of Astrophysics, Bangalore 560034, India
2National Astronomical Observatory of Japan, Mitaka, Japan
Abstract. It is generally believed that the magnetic pressure is much higher than the gas pressure in the coronal loops and these loops are isothermal in nature. We made systematic observations of four strong coronal emission lines in the visible and near infrared part of the spectrum for about 8 years. Two emission lines were observed at a time, making raster scans of a steady coronal region. We studied the variation of line widths of these lines and intensity ratios as a function of height. The relationship between the widths of these lines and intensity ratios indicates that the steady coronal loops are not magnetically isolated. These findings put restrictions on coronal loop models and indicate that the magnetic pressure in coronal loops may be much less than assumed. These results strongly suggest that magnetic field strength in the corona needs to be measured accurately.
Keywords: solar corona - coronal loops - emission lines - spectroscopy - line width - intensity ratio