A non-LTE study of neutral calcium in late-type stars with special reference to Pollux

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Abstract
Detailed simultaneous radiative transfer–statistical equilibrium calculations have been undertaken for neutral calcium using model stellar atmospheres corresponding to a variety of late spectral types. The results are used to investigate non-LTE effects and trends with differing stellar parameters, and to estimate the likely influence of departures from LTE on model atmosphere analyses. The behavior of individual Ca I atomic levels and lines is discussed in connection with calculations carried out for a model atmosphere corresponding to the K0 III giant Pollux (β Gem). Non-LTE effects in Ca I in solar-type dwarf stars are likely to be insignificant, but are expected to become increasingly significant toward lower gravity stars, with individual multiplets indicating widely different abundances in giant stars. Overionization effects are not expected to increase in severity in metal-poor stars due to a decrease in photospheric temperature gradient with decreasing metailicity, and in giant stars and hotter solar-type dwarfs because of enhancements of the Balmer continuous opacity in these spectral types.

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