Échelle diagram of p modes with (quasi-)regular frequency spacing from the Fourier spectrum of KIC 8975515 (Table 2). Symbol size refers to the amplitude of the p modes. Color coding and symbols are similar to Fig. 3. The symbol size is associated with the mode amplitudes. Panel a: frequency modulo of the mean rotational frequency spacing value associated with the slowly-rotating star, 0.419 d⁻¹ (magenta circles), was plotted twice. Panel b: frequency modulo of the mean rotational frequency spacing value associated with the fast-rotating star, 1.654 d⁻¹ (blue squares), was plotted twice.