Local value of the exponent α_B of the background as derived from Eq. (3), as a function of ν_max. The dashed line indicates the median value estimated in the range [5, 120 μHz]. The increase of α_B at large frequency is an artefact due to the Nyquist frequency. The color code indicates the evolutionary status: clump stars in red, red giant branch stars in blue, and undetermined status in black.