The intensities of helium lines in the solar EUV spectrum.
Abstract
The present paper points out that the lines of neutral and singly ionized helium in the solar EUV spectrum have anomalously high intensities when compared with lines of other ions formed at similar temperatures. It is suggested that the observed absolute and relative intensities, and, in addition, the line widths, can be accounted for if a mechanism which causes the helium atoms and ions to be excited by electrons with temperatures greater than the ionization equilibrium value is operating. Further, the observed decrease of helium line intensities in coronal holes, while other transition-region lines decrease little if at all, can be accounted for by the reduction of the enhancement mechanism in coronal holes and/or by the reduced temperature gradient in these regions. An essential factor that makes the helium lines so sensitive to the presence of such a mechanism is the large value of the ratio of the excitation potential of the lines to the electron temperature.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 1975
- DOI:
- 10.1093/mnras/170.2.429
- Bibcode:
- 1975MNRAS.170..429J
- Keywords:
-
- Far Ultraviolet Radiation;
- Helium Ions;
- Line Spectra;
- Solar Spectra;
- Spectral Line Width;
- Ultraviolet Spectra;
- Atomic Energy Levels;
- Atomic Spectra;
- Electron Energy;
- Emission Spectra;
- Helium Atoms;
- Luminous Intensity;
- Mathematical Models;
- Optical Thickness;
- Temperature Effects;
- Solar Physics