Échelle diagram for ℓ = 1 (left) and ℓ = 2 (right). Detected modes are marked according to their period on the abscissa, with a cyclic folding on the asymptotic period on the ordinate axis. The right-hand axis gives the order n of the mode, according to the asymptotic relation (Eq. (4)). Blue circles mark modes identified as ℓ = 1, with outlined cyan circles indicating those that appear in multiplets. Red squares mark ℓ = 2 modes, again with outlined points indicating multiplets. Cyan diamonds mark trapped ℓ = 1 modes, red diamonds mark trapped ℓ = 2 modes, and green diamonds mark modes that do not fit either sequence. Outlined cyan squares indicate modes that can be either ℓ = 1 or ℓ = 2. The high-amplitude peaks (A > 250 ppm) in the full dataset are marked with enlarged symbols.