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

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 $0.897673\pm 0.000004$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.

18 pages, 10 figures, 4 tables, accepted for publication in A&A

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