Detecting axisymmetric magnetic fields using gravity modes in intermediate-mass stars

¹ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, Leuven 3001, Belgium
e-mail: jordan.vanbeeck@kuleuven.be
² AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, Gif-sur-Yvette 91191, France
³ LESIA, Observatoire de Paris, PSL University, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, Meudon 92195, France
⁴ Department of Astrophysics, IMAPP, Radboud University Nijmegen, Nijmegen 6500 GL, The Netherlands
⁵ Max Planck Institute for Astronomy, Koenigstuhl 17, Heidelberg 69117, Germany

Received: 19 December 2019
Accepted: 4 May 2020

Abstract

Context. Angular momentum (AM) transport models of stellar interiors require improvements to explain the strong extraction of AM from stellar cores that is observed with asteroseismology. One of the frequently invoked mediators of AM transport are internal magnetic fields, even though their properties, observational signatures, and influence on stellar evolution are largely unknown.

Aims. We study how a fossil, axisymmetric internal magnetic field affects period spacing patterns of dipolar gravity mode oscillations in main sequence stars with masses of 1.3, 2.0, and 3.0 M_⊙. We assess the influence of fundamental stellar parameters on the magnitude of pulsation mode frequency shifts.

Methods. We computed dipolar gravity mode frequency shifts due to a fossil, axisymmetric poloidal–toroidal internal magnetic field for a grid of stellar evolution models, varying stellar fundamental parameters. Rigid rotation was taken into account using the traditional approximation of rotation, and the influence of the magnetic field was computed using a perturbative approach.

Results. We find magnetic signatures for dipolar gravity mode oscillations in terminal-age main sequence stars that are measurable for a near-core field strength larger than 10⁵ G. The predicted signatures differ appreciably from those due to rotation.

Conclusions. Our formalism demonstrates the potential for the future detection and characterization of strong fossil, axisymmetric internal magnetic fields in gravity-mode pulsators near the end of core-hydrogen burning from Kepler photometry, if such fields exist.