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

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 investigate the pulsating magnetic B3.5V star HD 43317, infer its interior properties and assess whether the dipolar magnetic field with a surface strength of B _p = 1312 ± 332 G causes different properties compared to those of non-magnetic stars. We analyze the latest version of the star’s 150 d CoRoT light curve and extract 35 significant frequencies, 28 of which are found to be independent and not related to the known surface rotation period of P _rot = 0.897673 d. We perform forward seismic modeling based on non-magnetic, non-rotating 1D MESA models and the adiabatic module of the pulsation code GYRE, using 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 _rot. This modeling is able to explain 16 of the 28 frequencies as gravity modes belonging to retrograde modes with ( ℓ, m) = (1, −1) and (2, −1) period spacing patterns and one distinct prograde (2, +2) mode. The modeling resulted in a stellar mass M _⋆ = 5.8 _−0.2 ^+0.1 M _⊙, a central hydrogen mass fraction X _c  = 0.54 _−0.02 ^+0.01, and exponential convective core overshooting parameter f _ov = 0.004 _−0.002 ^+0.014. The low value for f _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. We assess the frequency shifts of pulsation modes caused by the Lorentz and the Coriolis forces and find magnetism to have a lower impact than rotation for this star. Including magnetism in future pulsation computations would be highly relevant to exploit current and future photometric time series spanning at least one year, such as those assembled by the Kepler space telescope and expected from the TESS (Continuous Viewing Zone) and PLATO space missions.