The solar XUV He I and He II emission lines. I. Intensities and gross center-to-limb behavior.
Abstract
The center-to-limb variation of the He II 304- and 256-A lines and He I 584- and 537-A lines is derived for different solar features, but averaged over the chromospheric supergranulation structure. The general trend is for limb brightening in quiet-sun regions, limb neutrality in unipolar magnetic regions (UMR), and limb darkening in polar coronal holes. The center-to-limb behavior in these optically thick emission lines indicates collisional excitation and decreasing transition-region temperature gradients with respect to optical depth in the sequence quiet sun to UMR to coronal hole.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1978
- DOI:
- 10.1086/155952
- Bibcode:
- 1978ApJ...220..683M
- Keywords:
-
- Chromosphere;
- Helium Ions;
- Limb Darkening;
- Solar Corona;
- Spectroheliographs;
- Ultraviolet Spectra;
- Data Reduction;
- Electron Scattering;
- Resonant Frequencies;
- Solar Radiation;
- Temperature Gradients;
- Solar Physics;
- Extreme UV:Solar Chromosphere;
- Limb Darkening:Sun;
- Line Intensities:Solar Spectrum