The infrared triplet lines of ionized calcium as a diagnostic tool for F, G, K-type stellar atmospheres

LTE calculations of the profiles of the infrared triplet lines of ionized calcium in the spectrum of F, G and K stars are described in detail with explicit quantitative consideration of their perturbation by hydrogen Paschen lines. The results of such calculations obtained with five different solar model atmospheres are discussed. The sensitivity of the profiles to changes in basic stellar atmospheric parameters is illustrated. The flux in the center of the lambda 8542 Ä line is related empirically to the Mount-Wilson chromospheric activity indicator R'_HK. The predictive power of observations of the infrared triplet lines is then summed up.