Forward seismic modelling of the pulsating magnetic B-type star HD 43317

TL;DR

This study uses asteroseismology and forward seismic modelling to investigate the internal structure of the magnetic B-type star HD 43317, revealing its mass, age, and core overshooting, and assessing magnetic effects on stellar mixing.

Contribution

First detailed seismic analysis of a magnetic B-type star, estimating its internal properties and exploring magnetic influence on stellar structure and mixing.

Findings

Mode identification of gravity and prograde modes.

Estimated stellar mass ~5.8 solar masses.

Derived core overshooting parameter compatible with magnetic suppression.

Abstract

The large-scale magnetic fields detected at the surface of about 10% of hot stars extend into the stellar interior, where they may alter the structure. Deep inner regions of stars are only observable using asteroseismology. Here, we investigated the pulsating magnetic B3.5V star HD43317, inferred its interior properties and assessed whether the dipolar magnetic field with a surface strength of $B_p = 1312 \pm 332$G caused different properties compared to those of non-magnetic stars. We analysed the latest version of the star's 150d CoRoT light curve and extracted 35 significant frequencies, 28 of which were determined to be independent and not related to the known surface rotation period of $P_{\rm rot} = 0.897673$d. We performed forward seismic modelling based on non-magnetic, non-rotating 1D MESA models and the adiabatic module of the pulsation code GYRE, utilizing a grid-based approach. Our aim was to estimate the stellar mass, age, and convective core overshooting. The GYRE calculations were done for uniform rotation with $P_{\rm rot}$. This modelling was able to explain 16 of the 28 frequencies as gravity modes belonging to retrograde modes with $(\ell, m) = (1, -1)$ and $(2, -1)$ period spacing patterns and one distinct prograde $(2,2)$ mode. The modelling resulted in a stellar mass $M_{\star} = 5.8^{+0.1}_{-0.2}$$\mathrm{M_{\odot}}$, a central hydrogen mass fraction $X_c = 0.54^{+0.01}_{-0.02}$, and exponential convective core overshooting parameter $f_{\rm ov} = 0.004^{+0.014}_{-0.002}$. The low value for $f_{\rm ov}$ is compatible with the suppression of near-core mixing due to a magnetic field but the uncertainties are too large to pinpoint such suppression as the sole physical interpretation. $[...]$