Estimate of ΔΠ₁ for KIC7778197 (left panels) and KIC7509923 (right panels) using the method presented in Sect. 5.2 and Appendix A. Top panel: optimal values of χ² (see Eq. (A.9)) obtained for each tested value of ΔΠ₁. The vertical dotted line indicates the best fit to the data. Bottom panel: oscillation spectrum shown in the shape of an échelle diagram. Blue vertical dashed lines correspond to the best fit to the detected peaks, which are indicated as red vertical solid lines. No clear signature of rotation was found in the spectrum of KIC7778197, whereas it is evident for KIC7509923 (see text).