Abstract
Context.Stellar magnetic fields are often invoked to explain the missing transport of angular momentum observed in models of stellar interiors. However, the properties of an internal magnetic field and the consequences of its presence on stellar evolution are largely unknown.Aims.We study the effect of an axisymmetric internal magnetic field on the frequency of gravity modes in rapidly rotating stars to check whether gravity modes can be used to detect and probe such a field.Methods.Rotation is taken into account using the traditional approximation of rotation and the effect of the magnetic field is computed using a perturbative approach. As a proof of concept, we compute frequency shifts due to a mixed (i.e. with both poloidal and toroidal components) fossil magnetic field for a representative model of a known magnetic, rapidly rotating, slowly pulsating B-type star: HD 43317.Results.We find that frequency shifts induced by the magnetic field scale with the square of its amplitude. A magnetic field with a near-core strength of the order of 150 kG (which is consistent with the observed surface field strength of the order of 1 kG) leads to signatures that are detectable in period spacings for high-radial-order gravity modes.Conclusions.The predicted frequency shifts can be used to constrain internal magnetic fields and offer the potential for a significant step forward in our interpretation of the observed structure of gravity-mode period spacing patterns in rapidly rotating stars.
Highlights
The development of helio- and asteroseismology in recent decades has drastically improved our knowledge of stellar interiors
The goal of the present study is to develop a perturbative description of gravito-inertial modes in the presence of a stable, mixed, axisymmetric magnetic field within the traditional approximation of rotation (TAR)
In the present work we investigated the effect of a mixed, axisymmetric, internal large-scale magnetic field, which presumably is of fossil origin, on the oscillation frequencies of gravito-inertial modes in the traditional approximation of rotation
Summary
The development of helio- and asteroseismology in recent decades has drastically improved our knowledge of stellar interiors (see e.g. Aerts et al 2010, 2019; Chaplin & Miglio 2013; Hekker & Christensen-Dalsgaard 2017). Buysschaert et al (2018) considered the magnetic, rapidly rotating SPB star HD 43317, following the earlier studies of Pápics et al (2012), Briquet et al (2013), and Buysschaert et al (2017) They computed magnetic splittings due to an axisymmetric, purely poloidal dipolar field in the nonrotating case (following the perturbative formalism of Hasan et al 2005) and found that they were negligible with respect to rotational splittings, justifying the perturbative approach. The authors combined photometric and spectroscopic time series to perform mode identification and modelled the star using a grid of non-rotating, non-magnetic equilibrium stellar structure models They found tentative evidence for a low amount of convective core overshooting, which was interpreted as being caused by the large-scale magnetic field in HD 43317 (see Briquet et al 2012).
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