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Aims.Non-local thermodynamical equilibrium (NLTE) line formation for neutral and singly-ionized calcium is considered through a range of spectral types when the Ca abundance varies from the solar value down to Ca/H = -5. We evaluate the influence of departures from LTE on Ca abundance determinations and inspect the possibility of using / line-strength ratios as indicators of surface gravity for extremely metal-poor stars.
Mashonkina et al. (Wed,) studied this question.