Various morphologies observed in the power spectra of suppressed-dipole mode red giants

The Kepler mission provided light curves for over 16,000 red giants, of which a small fraction show reduced power in the dipole modes. We analysed both the radial and dipole modes in the power spectra of almost 600 red giants with low dipole-mode amplitudes. We found that the radial modes are unaffected by the suppression, suggesting that the suppression is mostly active in the central regions of the star. Moreover, we confirm that the majority of these stars still have observable mixed dipole modes, i.e., no complete suppression of the contribution from the inner regions to the dipole modes. This is in contradiction with the assumption of certain suppression mechanisms proposed in the literature. Finally, we also find different types of frequency-dependent suppression in the power spectra related to the stellar evolution. These new suppression types can lead to new constraints on and insights into the suppression mechanism(s) at play.