a) Period and period spacings for Model 4 (filled circles) and Model 1 (empty squares) from Table 3. The observed pattern is shown in grey. b) The frequency difference between model frequencies and those detected in the observations δf_i from Eq. (6). Compared to Fig. 1b, the ordinate is enlarged 40 times; the grey band around zero is the 1σ frequency uncertainty range σ_i. A similar plot for Model 4, Model 8, and Model 11 is shown in Figs. A.1 and A.2 in the Appendix.