Topology and obliquity of core magnetic fields in shaping seismic properties of slowly rotating evolved stars

Abstract

It is thought that magnetic fields must be present in the interiors of stars to resolve certain discrepancies between theory and observation (e.g. angular momentum transport), but such fields are difficult to detect and characterise. Asteroseismology is a powerful technique for inferring the internal structures of stars by measuring their oscillation frequencies, and succeeds particularly with evolved stars, owing to their mixed modes, which are sensitive to the deep interior. The goal of this work is to present a phenomenological study of the combined effects of rotation and magnetism in evolved stars, where both are assumed weak enough that first-order perturbation theory applies, and we focus on the regime where Coriolis and Lorentz forces are comparable. Axisymmetric "twisted-torus" field configurations are used, which are confined to the core and allowed to be misaligned with respect to the rotation axis. Factors such as the field radius, topology and obliquity are examined. We observe that fields with finer-scale radial structure and/or smaller radial extent produce smaller contributions to the frequency shift. The interplay of rotation and magnetism is shown to be complex: we demonstrate that it is possible for nearly symmetric multiplets of apparently low multiplicity to arise even under a substantial field, which might falsely appear to rule out its presence. Our results suggest that proper modelling of rotation and magnetism, in a simultaneous fashion, may be required to draw robust conclusions about the existence/non-existence of a core magnetic field in any given object.

arXiv comment19 pages, 20 figures, accepted for publication in MNRAS

References in corpus (41)

• Magnetic fields of non-degenerate stars
• Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
• Fast core rotation in red-giant stars revealed by gravity-dominated mixed modes
• Spin down of the core rotation in red giants
• Stable magnetic fields in stellar interiors
• Slowing the Spins of Stellar Cores
• Angular Momentum Transport in Stellar Interiors
• Minute-Timescale >100 MeV gamma-ray variability during the giant outburst of quasar 3C 279 observed by Fermi-LAT in 2015 June
• Characterization of the power excess of solar-like oscillations in red giants with Kepler
• The MiMeS Survey of Magnetism in Massive Stars: Introduction and overview
• Asteroseismology Can Reveal Strong Internal Magnetic Fields in Red Giant Stars
• Simulations of core convection in rotating A-type stars: Magnetic dynamo action
• A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Transport and mixing in the radiation zones of rotating stars II. Axisymmetric magnetic field
• Period spacings in red giants I. Disentangling rotation and revealing core structure discontinuities
• On the Stability of Non Force-Free Magnetic Equilibria in Stars
• Forward seismic modelling of the pulsating magnetic B-type star HD 43317
• Asteroseismic signatures of evolving internal stellar magnetic fields
• Dipole modes with depressed amplitudes in red giants are mixed modes
• Asteroseismology of evolved stars to constrain the internal transport of angular momentum II. Test of a revised prescription for transport by the Tayler instability
• Modeling of Magneto-Rotational Stellar Evolution I. Method and first applications
• Study of KIC 8561221 observed by Kepler: an early red giant showing depressed dipolar modes
• Period spacings of gravity modes in rapidly rotating magnetic stars I. Axisymmetric fossil field with poloidal and toroidal components
• Conversion of Internal Gravity Waves into Magnetic Waves
• Effect of a fossil magnetic field on the structure of a young Sun
• Asteroseismology and Oblique Pulsator Model of Beta Cephei
• Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants
• Normal Modes of Rotating Magnetic Stars
• Probing the internal magnetic field of slowly pulsating B-stars through g modes
• Detecting axisymmetric magnetic fields using gravity modes in intermediate-mass stars
• Period spacings of gravity modes in rapidly rotating magnetic stars II. The case of an oblique dipolar fossil magnetic field
• Discovery of the magnetic field in the pulsating B star beta Cephei
• Effect of a strong magnetic field on gravity-mode period spacings in red giant stars
• Effects of a strong magnetic field on internal gravity waves: trapping, phase mixing, reflection and dynamical chaos
• Magnetic Helicity and the Relaxation of Fossil Fields
• Magneto-gravity wave packet dynamics in strongly magnetised cores of evolved stars
• Probing the internal solar magnetic field through g-modes
• Core magnetic field imprint in the non-radial oscillations of red giant stars
• Probing the Missing Link between the Diffuse Interstellar Bands and the Total-to-Selective Extinction Ratio $R_V$ $-$ I. Extinction versus Reddening
• Low-degree mixed modes in red giant stars with moderate core magnetic fields

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• Mode Mixing and Rotational Splittings: I. Near-Degeneracy Effects Revisited
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• Oscillations of red giant stars with magnetic damping in the core. I. Dissipation of mode energy in dipole-like magnetic fields
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