The dynamical properties of the solar corona from intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII.
Abstract
We have studied the line profiles of the solar coronal forbidden lines Si viii 1445.76 A, Fe XI 1467.08 A, and Fe xii 1242.03 A in quiet and active coronal regions from a survey of available limb spectra in the NRL Skylab data. The results show that the line widths of these lines are essentially the same in quiet-Sun regions as in active regions. For some active regions, however, the line widths are systematically narrower than those in quiet-Sun regions. In addition, the line widths are about the same in the height range from 0" to 30 . The widths are wider than the thermal Doppler widths at the ionization equilibrium temperature given by Jordan. The additional widths correspond to a nonthermal mass-motion velocity of 10-25 km -1 at 1.7 x 106 K (Fe xii), 10-17 km -1 at 1.5 x 10 K (Fe xi), and 10-20 km -1 at 9.3 x 10 K (Si viii). The intensities of the forbidden lines in active regions are about an order of magnitude greater than those in quiet-Sun regions. The distribution of column density calculated for the three different lines indicates that more plasma is near 1.7 x 106 K than near 9.3 x 10 K at a given height. The observational results are discussed in terms of coronal heating mechanisms. The dissipation of acoustic waves does not provide a sufficient heating rate. The dissipation of three modes of hydromagnetic waves-the slow mode, the fast mode, and the AlfVe'n mode-also cannot satisfactorily explain the observational results. It is difficult for heating by hydromagnetic waves to meet simultaneously the requirements of a large enough heating rate, a dissipation length comparable to the length of a coronal loop, and a velocity amplitude that agrees with observations. Subject headings: line profiles - Sun: corona - Sun: spectra - ultraviolet: spectra
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1979
- DOI:
- 10.1086/156811
- Bibcode:
- 1979ApJ...227.1037C
- Keywords:
-
- Forbidden Bands;
- Solar Corona;
- Solar Spectra;
- Spectral Line Width;
- Ultraviolet Astronomy;
- Emission Spectra;
- Far Ultraviolet Radiation;
- Iron;
- Magnetohydrodynamic Waves;
- Propagation Modes;
- Silicon;
- Solar Physics;
- Extreme UV:Solar Corona;
- Forbidden Lines:Solar Corona;
- Line Profiles:Solar Corona;
- Solar Corona:Heating