Observed and synthetic photometric variations of M-type AGB stars. Upper panels: photometric variations for a sample of observed targets, derived from sine fits of light-curves (see Fig. 4 and related text for details). Lower panels: photometric variations for the core-mantle grain models listed in Table 4 with colors calculated from sine fits of the light-curves, same as for the observational data in the top panels; the lines are color-coded by stellar parameters and pulsation amplitude.