Frequency spectrum of the star 241 with sequential prewhitening. Some characteristic frequencies are labeled with their identification. Sat refers to frequencies connected to the orbit of the CoRoT satellite. a) The original spectrum dominated by the first overtone pulsation mode (f₁). b) After prewhitening with f₁ and its harmonics. c) The result of removing f′ and all combination terms involving f₁ and f′. d) Prewhitening with all f₁ ± k ∗ f_m and f′ ± k ∗ f_m frequencies. e) After removing all significant f₁ ± k ∗ f_b and f′ ± k ∗ f_b frequencies. f) Removing another 13 frequencies including those from the satellite and third order linear combinations of {f₁,f′,f_m,f_b}.