Observation and Interpretation of Rare Earth Spectra.
Abstract
We have observed spectral lines of the rare earth ion Ce II in the wavelength range 4000-4700 A. Photoelectric and photographic observations cover the disk from its center to beyond the limb. The height resolution of the observations near the limb is enhanced through Fourier transform techniques. The residual spread function has 0.7-1.4 sec of arc half-width at half-maximum, and low-amplitude wings. The observed chromospheric emission line profiles yield 2.0+0.1 km/ sec non-thermal broadening velocities in the height range 0 <h <400 km. The observed Ce II lines reverse from absorption to emission on the disk. The reversal height depends on wavelength. At shorter wavelengths emission lines extend farther onto the disk. The center-limb variation of absorption line equivalent widths is analyzed by Altrock's method (Ph.D. thesis, University of Colorado, 1967). The ratio of the line- to-continuum source functions S/B >1, and increases with decreasing wavelength. This suggests that scattering contributes to the line source function. Athay and Skumanich's method (Ann. Astrophys. 30, 669,1967) is used with recent solar models to calculate pure absorption and pure noncoherent scattering line profiles. Noncoherent scattering produces better agreement with the observed profiles. The atmospheric parameters that provide the best agreement with the observed absorption lines are then applied to the extreme limb spectra. Using these parameters, noncoherent scattering also correctly predicts both the existence of emission lines on the disk and the observed wavelength dependence of the reversal height.
- Publication:
-
The Astronomical Journal Supplement
- Pub Date:
- 1968
- Bibcode:
- 1968AJS....73Q..57C