Discovery of a magnetic field in the CoRoT hybrid B-type pulsator HD 43317

TL;DR

This study directly detected a magnetic field in the hybrid B-type pulsator HD 43317, revealing an oblique dipolar magnetic field of about 1 kG, which impacts future asteroseismic modeling of the star.

Contribution

First direct detection and characterization of a magnetic field in the hybrid pulsator HD 43317, linking magnetic properties with pulsational and rotational behavior.

Findings

Zeeman signatures clearly detected in HD 43317

Magnetic field is oblique and dipolar with about 1 kG strength

Magnetic modulation matches the star's rotation period

Abstract

A promising way of testing the impact of a magnetic field on internal mixing (core overshooting, internal rotation) in main-sequence B-type stars is to perform asteroseismic studies of a sample of magnetic pulsators. The CoRoT satellite revealed that the B3IV star HD 43317 is a hybrid SPB/beta Cep-type pulsator that has a wealth of pulsational constraints on which one can perform a seismic modelling, in particular, probing the extent of its convective core and mixing processes. Moreover, indirect indicators of a magnetic field in the star were observed: rotational modulation due to chemical or temperature spots and X-ray emission. Our goal was to directly investigate the field in HD 43317 and, if it is magnetic, to characterise it. We collected data with the Narval spectropolarimeter installed at TBL (T\'elescope Bernard Lyot, Pic du Midi, France) and applied the least-squares deconvolution technique to measure the circular polarisation of the light emitted from HD 43317. We modelled the longitudinal field measurements directly with a dipole. Zeeman signatures in the Stokes V profiles of HD 43317 are clearly detected and rotationally modulated, which proves that this star exhibits an oblique magnetic field. The modulation with the rotation period deduced from the CoRoT light curve is also confirmed, and we found a field strength at the poles of about 1 kG. Our result must be taken into account in future seismic modelling work of this star.