Power spectrum fit of the oscillating stars of the sample. Left: background fitting. The gray line represents the power spectral density and the black line corresponds to its smoothed version. The sum of the two super-Lorentzian functions and the white noise model is shown in red and the total background, with the Gaussian envelope of the modes, in green. See Sect. 3.1.1 for a description of the method. Right: an échelle diagram. The blue, green, and red lines correspond to the ridges of the radial, dipolar, and quadrupolar modes, respectively. These curves were computed from Eqs. (1)–(3). The dashed horizontal line indicates the value of ν_max. The value of Δν is reported under the x-axis.