Dip formation in the gravity-mode period spacing pattern: The magnetic picture

Understanding angular momentum transport is a major challenge for the theory of stellar evolution. Recent asteroseismic studies from Kepler detected dips in the gravity-mode period spacing vs period diagram of γ Doradus stars. One of the mechanisms causing such dips is the interaction of gravito-inertial modes in the radiative envelope with pure inertial modes in the convective core. In this work, we derive the effect of internal magnetic fields on the Lorentzian shape of the dip, magnetic fields being one of the main candidates to efficiently redistribute angular momentum throughout stellar evolution. For this, considering a toroidal magnetic topology corresponding to a uniform Alfvén frequency in the radiative envelope and in the convective core, we study the wave behavior in both regions and we demonstrate that the magneto-hydrodynamic coupling problem shows similarities with the pure hydrodynamic case. We identify the three main influences of the magnetic field: a shift of the average period spacing in the co-rotating frame, an additional decrease of the period spacing pattern in period, and a shift of the period of the dip in the inertial frame. We extend the study to non-Kelvin modes previously detected in γ Doradus stars. Our work demonstrates the remarkable potential of studying such dips to probe internal stellar magnetism and provides predictions for further detections in asteroseismic data.