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 investigated the pulsating magnetic B3.5V star HD 43317, inferred its interior properties and assessed whether the dipolar magnetic field with a surface strength of B p = 1312 ± 332 G caused different properties compared to those of non-magnetic stars. We analysed the latest version of the star's 150 d 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 rot = 0.897673 d. We performed forward seismic modelling based on non-magnetic, nonrotating 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 rot . This modelling was able to explain 16 of the 28 frequencies as gravity modes belonging to retrograde modes with ( , m) = (1, −1) and (2, −1) period spacing patterns and one distinct prograde (2, 2) mode. The modelling resulted in a stellar mass M = 5.8 +0.1 −0.2 M , a central hydrogen mass fraction X c = 0.54 +0.01 −0.02 , and exponential convective core overshooting parameter f ov = 0.004 +0.014 −0.002 . 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 assessed the frequency shifts of pulsation modes caused by the Lorentz and the Coriolis forces and found 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.

Asteroseismic masses, ages, and core properties of γ Doradus stars using gravito-inertial dipole modes and spectroscopy

“…Therefore, it is expected that high-mass γ Dor stars are slow rotators since they are closer to the TAMS than low-mass stars. Yet, the fact we do not observe any evolved fast rotators might also be caused by an observational selection bias, because the structure of a TAMS star combined with fast rotation creates a dense, and typically unresolvable spectrum of pulsation modes (e.g., Buysschaert et al 2018). Nevertheless, the fact that the fastest rotators in our sample are all found to be relatively young suggests that the transport of angular momentum from the core to the envelope must be efficient already early on in the stellar evolution.…”

Isochrone-cloud fitting of the extended main-sequence turn-off of young clusters

“…The asteroseismically calibrated levels of core overshooting led to values between typically 0.1 and 0.5 times the local pressure scale height, resulting in increased core masses compared to standard SSE models without extra mixing at the near-core boundary. With the exception of one magnetic g-mode pulsator (Buysschaert et al 2018), higherthan-standard core masses were found for almost all studied g-mode pulsators of intermediate mass (some 50 stars), covering the entire core-hydrogen burning phase, irrespective of their level of rotation.…”

The mass discrepancy in intermediate- and high-mass eclipsing binaries: The need for higher convective core masses

“…A notable characteristic of the primary component of V380 Cyg is its high value of the required microturbulent velocity ξ = 15 ± 1 km s −1 as measured by Tkachenko et al (2014) from high-resolution optical spectra. Having high values of the microturbulent velocity is a common phenomenon in massive evolved stars as demonstrated by Cantiello et al (2009) from samples of high-mass stars in the Galaxy and in the LMC. The authors also report a strong anti-correlation between the observed microturbulent velocities and stellar surface gravities, namely ξ tends to increase as log g decreases.…”

“…Stellar evolution dictates the formation of a sub-surface convection zone in high-mass stars as they approach the Terminal Age Main-Sequence (TAMS), giving rise to a higher microturbulent velocity field (e.g., Cantiello et al 2009). Ignoring the effect of microturbulence by fixing it to 2 km s −1 in stellar atmosphere models implies overestimation of the effective temperature of the star by means of a spectroscopic analysis.…”