Effect of a strong magnetic field on gravity-mode period spacings in red giant stars

Abstract

When a star evolves into a red giant, the enhanced coupling between core-based gravity modes and envelope-based pressure modes forms mixed modes, allowing its deep interior to be probed by asteroseismology. The ability to obtain information about stellar interiors is important for constraining theories of stellar structure and evolution, for which the origin of various discrepancies between prediction and observation are still under debate. Ongoing speculation surrounds the possibility that some red giant stars may harbour strong (dynamically significant) magnetic fields in their cores, but interpretation of the observational data remains controversial. In part, this is tied to shortfalls in our understanding of the effects of strong fields on the seismic properties of gravity modes, which lies beyond the regime of standard perturbative methods. Here we seek to investigate the effect of a strong magnetic field on the asymptotic period spacings of gravity modes. We use a Hamiltonian ray approach to measure the volume of phase space occupied by mode-forming rays, this being roughly proportional to the average density of modes (number of modes per unit frequency interval). A strong field appears to systematically increase this by about 10%, which predicts a ~10% smaller period spacing. Evidence of near integrability in the ray dynamics hints that the gravity-mode spectrum may still exhibit pseudo-regularities under a strong field.

14 pages, 11 figures, accepted for publication in MNRAS

References in corpus (12)

• Slowing the Spins of Stellar Cores
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Inhibition of thermohaline mixing by a magnetic field in Ap star descendants: Implications for the Galactic evolution of 3He
• Period spacings in red giants; III. Coupling factors of mixed modes
• An Elementary Introduction to the JWKB Approximation
• Period spacings of gravity modes in rapidly rotating magnetic stars I. Axisymmetric fossil field with poloidal and toroidal components
• Detecting axisymmetric magnetic fields using gravity modes in intermediate-mass stars
• Regular Oscillation Sub-spectrum of Rapidly Rotating Stars
• Asteroseismology of evolved stars to constrain the internal transport of angular momentum. III. Using the rotation rates of intermediate-mass stars to test the Fuller-formalism
• Period spacing of gravity modes strongly affected by rotation. Going beyond the traditional approximation
• Solar-like Oscillations: An Observational Perspective
• Low-degree mixed modes in red giant stars with moderate core magnetic fields

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• Magnetic signatures on mixed-mode frequencies. II. Period spacings as a probe of the internal magnetism of red giants
• Gravity waves in strong magnetic fields
• Detecting deep axisymmetric toroidal magnetic fields in stars. The traditional approximation of rotation for differentially rotating deep spherical shells with a general azimuthal magnetic field
• Spinning up the Surface: Evidence for Planetary Engulfment or Unexpected Angular Momentum Transport?
• In search of gravity mode signatures in main sequence solar-type stars observed by Kepler