Probing the shape of the mixing profile and of the thermal structure at the convective core boundary through asteroseismology

¹ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: mathias.michielsen@kuleuven.be
² AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sarbonne Paris Cité, 91191 Gif-sur-Yvette Cedex, France
³ Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands

Received: 23 April 2019
Accepted: 11 June 2019

Abstract

Aims. We investigate from a theoretical perspective if space asteroseismology can be used to distinguish between different thermal structures and shapes of the near-core mixing profiles for different types of coherent oscillation modes in massive stars with convective cores; we also examine whether this capacity depends on the evolutionary stage of the models along the main sequence.

Methods. We computed 1D stellar structure and evolution models for four different prescriptions of the mixing and temperature gradient in the near-core region. We investigated their effect on the frequencies of dipole prograde gravity modes in slowly pulsating B stars and in β Cep stars as well as pressure modes in β Cep stars.

Results. A comparison between the mode frequencies of the different models at various stages during the main sequence evolution reveals that they are more sensitive to a change in temperature gradient than to the exact shape of the mixing profile in the near-core region. Depending on the duration of the observed light curve, we can distinguish between either just the temperature gradient, or also between the shapes of the mixing coefficient. The relative frequency differences are in general larger for more evolved models and are largest for the higher frequency pressure modes in β Cep stars.

Conclusions. In order to unravel the core boundary mixing and thermal structure of the near-core region, we must have asteroseismic masses and radii with ∼1% relative precision for hundreds of stars.