Sub-Inertial Gravity Modes in the B8v Star Kic 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

Abstract

Thus far, KIC 7760680 is the richest slowly pulsating B star, exhibiting 36 consecutive dipole (ℓ = 1) gravity (g-) modes. The monotonically decreasing period spacing of the series, in addition to the local dips in the pattern, confirm that KIC 7760680 is a moderate rotator with clear mode trapping in chemically inhomogeneous layers. We employ the traditional approximation of rotation to incorporate rotational effects on g-mode frequencies. Our detailed forward asteroseismic modeling of this g-mode series reveals that KIC 7760680 is a moderately rotating B star with mass ∼3.25 M e . By simultaneously matching the slope of the period spacing and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 day −1 , which is 26% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than 1%. We succeed in tightly constraining the exponentially decaying convective core overshooting parameter to f ov ≈ 0.024 ± 0.001. This means that convective core overshooting can coexist with moderate rotation. Moreover, models with exponentially decaying overshoot from the core outperform those with the classical step-function overshoot. The best value for extra diffusive mixing in the radiatively stable envelope is confined to »  D log 0.75 0.25 ext (with D ext in cm 2 s −1 ), which is notably smaller than theoretical predictions.

Magnetic characterization of the SPB/β Cep hybrid pulsator HD 43317

“…In a future paper, the observed pulsation modes will be used to constrain the stellar structure through forward modeling (as done in, e.g., Degroote et al 2010;Pápics et al 2015;Van Reeth et al 2016;Moravveji et al 2016). At this stage, however, we can already employ several theoretical criteria to study whether or not the magnetic field at the stellar surface of HD 43317 is sufficiently strong to imply solid-body rotation.…”

Constraining the near-core rotation of theγDoradus star 43 Cygni using BRITE-Constellation data

“…The convection was treated using the mixing-length theory, with α MLT equal to 1.8, and the models include exponential core overshooting, assuming f ov equal to 0.015. These parameter values were chosen to be close to typical values found in the literature for main-sequence g-mode pulsators (e.g., Moravveji et al 2015Moravveji et al , 2016Schmid & Aerts 2016).…”

The potential of space observations for pulsating pre-main sequence stars

“…For three of these objects first signs of period spacings are detected in photometric time series only ∼ 22 and ∼ 39 days long. Similar as in the case for pre-MS γ Doradus g-mode pulsators, the main aim is to find period spacings that lead to a better constraint on rotation and diffusive mixing in young stars as it was done already for main sequence stars (e.g., for KIC 7760680) [16,17].…”