Periodogram for KIC 10553698. This is the same FT as in Fig. 3, but with period on the abscissa. The first panel starts where the last panel in Fig. 3 ends, and frequencies shorter than the triplet at 86 μHz have been truncated. Radial order according to the asymptotic relation (Eq. (4)) is indicated on the top axis, with inward tick marks counting the ℓ = 1 spacing and outward tick marks counting the ℓ = 2 spacing.