Nov 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978soph...60...19.&link_type=abstract
behavior of Ca I lambda 6573 and Ca II lambda 7324. T. R. Ayres and L. Testerman (Kitt Peak National Observatory, Tucson, Ariz.)
Physics
Calcium, Line Spectra, Photosphere, Solar Spectra, Abundance, Forbidden Transitions, Photoionization, Spectral Line Width, Stellar Atmospheres, Stellar Models
Scientific paper
Center-to-limb measurements of the Ca I 6573 intercombination line and the Ca II 7324 forbidden line are compared with synthetic profiles based on a simple representation of the non-LTE Ca-Ca(+) ionization equilibrium. The effects of photoionizations from low lying excited states of neutral calcium are found to reduce the sensitivity of the 6573 center-to-limb behavior as a thermal structure diagnostic. The synthetic center-to-limb behavior is also sensitive to uncertainties in the nonthermal broadening. Nevertheless, the measured center-to-limb behavior of 6573 favors a 'cool' photospheric model over hotter models based on the Ca II K wings. The non-LTE calcium abundance obtained from the disk center equivalent widths of 6573 and 7324 using the best fit model is A(Ca) = 2.1 plus or minus 0.2 x 10 to the -6th (by number relative to hydrogen).
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