Tight asteroseismic constraints on core overshooting and diffusive mixing in the slowly rotating pulsating B8.3V star KIC 10526294

KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra diffusive mixing. We find a tight mass, metallicity relation within the ranges $M$ ~ 3.13 to 3.25 Msun and $Z$ ~ 0.014 to 0.028. We deduce that an exponentially decaying diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of $f_{ov}$ between 0.017 and 0.018. Moreover, the inclusion of extra diffusive mixing with a value of $\log D_{\rm mix}$ between 1.75 and 2.00 dex (with $D_{\rm mix}$ in cm^2/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra mixing is considered, irrespective of the $(M,Z)$ combination within the allowed seismic range. The inclusion of diffusive mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.Comment: 13 pages, 4 tables, 12 figures, accepted for publication in Astronomy & Astrophyic

Recipes for bolometric corrections and Gaia luminosities of B-type stars: Application to an asteroseismic sample

We provide three statistical model prescriptions for the bolometric corrections appropriate for B-type stars as a function of: 1) T_eff, 2) T_eff, log g, and 3) T_eff, log g, [M/H]. These statistical models have been calculated for 27 different filters, including those of the Gaia space mission, and were derived based on two different grids of bolometric corrections assuming LTE and LTE+NLTE, respectively. Previous such work has mainly been limited to a single photometric passband without taking into account NLTE effects on the bolometric corrections. Using these statistical models, we calculate the luminosities of 34 slowly pulsating B-type (SPB) stars with available spectroscopic parameters, to place them in the Hertzsprung-Russell diagram and compare their position to the theoretical SPB instability strip. We find that excluding NLTE effects has no significant impact on the derived luminosities for the temperature range 11500-21000 K. We conclude that spectroscopic parameters are needed in order to achieve meaningful luminosities of B-type stars. The three prescriptions for the bolometric corrections are valid for any galactic B-type star with effective temperatures and surface gravities in the ranges 10000-30000 K and 2.5-4.5 dex, respectively, covering regimes below the Eddington limit.Comment: 17 pages, 12 figures, accepted for publication in MNRA