Diagrams of the CoRoT light curve of HD 174648, folded on the dominant frequencies f₁ (top) and f₂ (bottom), after prewhitening all other detected frequencies. The top phase diagram clearly illustrates the non-sinusoidal shape of the variations for f₁; the nonsinusoidal shape for f₂ in the bottom diagram is less obvious, but is clearly demonstrated by the presence of the first harmonic of this frequency at 2f₂, labelled f₄ in Table 3.