The inertial dip in the period-spacing pattern of fast rotating γ-Dor stars results from the interaction of core and envelope modes. As such, it gives an unprecedented window on the convective core structure and dynamics. In this article, we build a theoretical framework enabling the analysis of the inertial dip's sensitivity to magnetism.
γ-Dor stars are ideal targets for studies of stellar innermost dynamical properties due to their rich asteroseismic spectrum of gravity modes. Integrating internal magnetism to the picture appears as the next milestone of detailed asteroseismic studies, for its prime importance on stellar evolution. The inertial dip in prograde dipole modes period-spacing pattern of γ-Dors stands out as a unique window on the convective core structure and dynamics. Recent studies have highlighted the dependence of the dip structure on core density stratification, contrast of the near-core Brunt- Väisälä frequency and rotation rate, as well as the core-to-near-core differential rotation. In the meantime, the effect of envelope magnetism has been derived on low-frequency magneto-gravito-inertial waves.
We aim to revisit the inertial dip formation including core and envelope magnetism, and explore the probing power of this feature on dynamo-generated core fields.
We consider as a first step a toroidal magnetic field with a bi-layer (core and envelope) Alfvén frequency. This configuration allows us to revisit the coupling problem using our knowledge on both core magneto-inertial modes and envelope magneto-gravito-inertial modes. Using this configuration, we can stay in an analytical framework to exhibit the magnetic effects on the inertial dip shape and location. This configuration allows to set up a laboratory towards the comprehension of magnetic effects on the dip structure.
We show a shift of the inertial dip towards lower spin parameter values and a thinner dip with increasing core magnetic field’s strength, quite similar to the signature of differential rotation. The magnetic effects become sizeable when the ratio between the magnetic and the Coriolis effects is large enough. We explore the potential degeneracy of the magnetic effects with differential rotation. We study the detectability of core magnetism, considering both observational constraints on the periods of the modes and potential gravito-inertial mode suppression.