Emission Cores in h- and K-Lines III. The Wilson-Bappu Effect
Abstract
Widths of the emission components, W2, of the H- and K-lines of Ca ii are investigated, assuming that the lines are formed in optically thick chromospheres with temperature increasing outward. The line source function S is computed from an equation relating S to the Planck function and the divergence of the line flux W2 is found to be particularly sensitive to chromospheric opacity both in the line and in the continuum, to the damping parameter a, and to the chromospheric Doppler width We interpret the results to mean that the Wilson-Bappu effect arises primarily from changes in Doppler width, and, fur- ther, that there is a tendency among the chromospheres of late-type stars to have approximately the same line and continuum opacities and to have a < 3 X 1O~. To a first approximation, the intensity of the emission component is found to be uncorrelated with W
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1968
- DOI:
- 10.1086/149532
- Bibcode:
- 1968ApJ...152..141A