Magnetic characterization of the SPB/$\mathbf{\beta}$ Cep hybrid pulsator HD 43317

TL;DR

This study characterizes the surface magnetic field of the hybrid pulsator HD 43317, revealing a strong dipolar magnetic field that influences its internal structure and pulsation behavior, with implications for stellar evolution modeling.

Contribution

It provides the first detailed measurement of the magnetic field geometry and strength in HD 43317, combining spectropolarimetry and a grid-based modeling approach.

Findings

Magnetic field strength is approximately 1-1.5 kG.

Obliquity angle between magnetic and rotation axes is 67-90 degrees.

Magnetic field influences internal rotation and convective core overshooting.

Abstract

Large-scale magnetic fields at the surface of massive stars do not only influence the outer-most layers of the star, but also have consequences for the deep interior, only observationally accessible through asteroseismology. We performed a detailed characterization of the dipolar magnetic field at the surface of the B3.5V star HD 43317, a SPB/$\beta$ Cep hybrid pulsator, by studying the rotationally modulated magnetic field of archival and new Narval spectropolarimetry. Additionally, we employed a grid-based approach to compare the Zeeman signatures with model profiles. By studying the rotational modulation of the He lines in both the Narval and HARPS spectroscopy caused by co-rotating surface abundance inhomogeneities, we updated the rotation period to $0.897673\pm0.000004$d. The inclination angle between the rotation axis and the observer's line of sight remains ill-defined, because of the low level of variability in Stokes V and deformations in the intensity profiles by stellar pulsation modes. The obliquity angle between the rotation and magnetic axes is constrained to $\beta \in [67,90]^{\circ}$, and the strength of the dipolar magnetic field is of the order of 1kG to 1.5kG. This magnetic field at the stellar surface is sufficiently strong to warrant a uniformly rotating radiative envelope, causing less convective core overshooting, which should be visible in future forward seismic modeling.