Dependency of Ca II IRT flux on metallicity. a. Example relation for a colour bin of B–V=0.62–0.63 for IRT-1 (log-linear presentation). Small dots are the data of 706 targets in this B–V bin. The line is a polynomial fit of the second order. b. Overplot of the polynomial fits for all B–V bins. c. Logarithmic radiative loss from the entire triplet and for the full available B–V range. The colour denotes the number density (darkest red is 600, darkest blue is 1 target).