Exploring the probing power of gamma-Dor's inertial dip to core magnetism

Inertial dips in the period-spacing pattern of fast-rotating γ-Dor stars observed by Kepler stand out as a unique window on their convective core dynamics, such as its rotation and internal magnetic field. They result from a core inertial - envelope gravito-inertial modes interaction (Ouazzani et al. 2020). Measurements of convective core magnetic field in γ-Dors would bear new constraints on dynamo generation and angular momentum transport during the main sequence of intermediate mass stars. Integrating these results with previous knowledge on red giants’ inner fields will bring a dynamical view on internal magnetic field evolution in this mass range, a cornerstone of modern stellar physics. We thus aim to explore the probing power of inertial dips for core magnetism, building on a first study on core-to-envelope differential rotation (Barrault et al. 2025). We consider a toroidal magnetic field configuration with uniform Alfvén frequencies in both the convective core and the radiative envelope. This framework allows for setting up an analytical laboratory towards the fine comprehension of the magnetic effects on the dip formation. We derive the coupling equation that we further solve, providing an analytical expression for the dip profile. We exhibit a dip shifted towards low periods and thinner with increasing core magnetic field. We investigate the detectability of the magnetic signature with three typical MESA γ-Dor models, exploring masses and rotation regimes across the instability strip. We discuss the degeneracy of magnetic and core-to-envelope differential rotation effects, and give hints on how to overcome the detection challenges. Our work shows the remarkable potential of the dip study to probe core processes quite similarly to mixed pressure-gravity modes in evolved stars. It advocates for integrating all effects known to alter the dip shape and location to perform future magnetic field detections in γ-Dor’s convective cores from asteroseismic data.