Silencing Stars: Upper limits on internal magnetic fields

Le résumé fourni par la source

Asteroseismology has shown that sufficiently strong internal magnetic fields can suppress gravity modes, preventing their propagation to the surface depending on their radial order. In this work, we place upper limits on the radial component of near-core magnetic fields in three pulsating stars using their observed gravity modes. We analyzed two main-sequence γ Doradus stars with many consecutive radial orders observed for modes of degree ℓ = 1, 2, 3 and rotational splitting, as well as one evolved δ Scuti star hosting mixed modes. For each target, we find best-fitting stellar models via forward modeling with MESA and compute adiabatic oscillation frequencies with GYRE. From magneto-hydrodynamical calculations in the Dedalus code, we determine the critical magnetic field strength required to suppress gravity modes of radial order higher than those observed. A variety of magnetic field configurations are explored, including poloidal fields with dipolar and quadrupolar components, and mixed geometries including a toroidal field.The targets were selected to study the impact of the mode degree and rotational splitting on our calculations. We find that the critical field strength required for mode suppression increases gradually with increasing spherical harmonic degree, up to ℓ = 3. Analysis of the individual components of the ℓ = 1 and ℓ = 2 rotational splittings further indicates that the inferred magnetic field strength is identical for prograde and retrograde modes. The resulting upper limits are consistent with magnetic field strengths measured in evolved red giants, supporting a scenario in which the observed fields originate from a core dynamo.

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