# Asteroseismic inference of the near-core magnetic field strength in the main sequence B star HD 43317

**Authors:** Daniel Lecoanet, Dominic M. Bowman, Timothy Van Reeth  
**arXiv:** [2202.03440](https://arxiv.org/abs/2202.03440)  
**Date:** 2022-02-07  
**Summary page:** https://www.summarizepaper.com/en/paper/2202.03440v1/

## Key points

- Recent advancements in asteroseismology have allowed for new insights into the study of magnetic fields in the interiors of stars.
- The pulsating and magnetic B star HD 43317 has been studied using asteroseismology to infer an upper limit for the magnetic field strength in its near-core region.
- A result of approximately $5 \times 10^5$ G was found to be sufficient to suppress high-radial order g modes and reproduce the observed frequency spectrum of HD 43317, which contains only high-frequency g modes.
- This is significant as it is the first inference of the magnetic field strength inside a main-sequence star.
- Previous studies on magnetism in stars include research on intermediate- and high-mass dwarf stars that host strong large-scale magnetic fields at their surface, thought to be of fossil field origin.
- Massive stars harbor convective cores while on the main sequence, making asteroseismology of g modes useful for providing constraints on core masses but not yet used to probe interior magnetic fields.
- The authors use data from various sources including A&A papers by Pápics et al., Prat et al., Van Beeck et al., and Townsend et al., as well as MNRAS papers by Wade et al., Paxton et al., Shultz et al., Stello et al., Van Reeth et al., and Townsend et al. They also reference other works such as Power's Master's thesis from Queen's University and Ricker et al.'s Journal of Astronomical Telescopes article.
- In this study, 20 best-fitting asteroseismic models were used to estimate critical magnetic field strengths for internal gravity waves (IGWs) with frequencies of ℓ = 2, npg = −16 (npg = −15) modes.
- The mean estimate across all 20 models was approximately 4 kG.
- This study provides valuable insights into the magnetic fields within stars and opens up new avenues for future research in this area.

## Summary

The study of magnetic fields in the interiors of stars has been a challenging task, but recent advancements in asteroseismology have allowed for new insights. In particular, the pulsating and magnetic B star HD 43317 has been studied using asteroseismology to infer an upper limit for the magnetic field strength in its near-core region. The interaction between a magnetic field and gravity (g) modes was used to constrain the magnetic field strength, with a result of approximately $5 \times 10^5$ G being sufficient to suppress high-radial order g modes and reproduce the observed frequency spectrum of HD 43317, which contains only high-frequency g modes. This finding is significant as it is the first inference of the magnetic field strength inside a main-sequence star. Previous studies on magnetism in stars include research on intermediate- and high-mass dwarf stars that host strong large-scale magnetic fields at their surface, thought to be of fossil field origin. However, there are few inferences about the magnetic field strength and geometry within deep interiors. Massive stars harbor convective cores while on the main sequence, making asteroseismology of g modes useful for providing constraints on core masses but not yet used to probe interior magnetic fields. The authors use data from various sources including A&A papers by Pápics et al., Prat et al., Van Beeck et al., and Townsend et al., as well as MNRAS papers by Wade et al., Paxton et al., Shultz et al., Stello et al., Van Reeth et al., and Townsend et al. They also reference other works such as Power's Master's thesis from Queen's University and Ricker et al. 's Journal of Astronomical Telescopes article. In this study, 20 best-fitting asteroseismic models were used to estimate critical magnetic field strengths for internal gravity waves (IGWs) with frequencies of ℓ = 2, npg = −16 (npg = −15) modes. The mean of these estimates was taken as an estimate of the stellar magnetic field resulting in a value of approximately 4 kG across all 20 models. This study provides valuable insights into the magnetic fields within stars and opens up new avenues for future research in this area.