Hydrodynamical instabilities induced by atomic diffusion in A stars and their consequences

¹ Laboratoire Univers et Particules de Montpellier (LUPM), UMR 5299, Université de Montpellier, CNRS, place Eugène Bataillon, 34095 Montpellier Cedex 5, France
e-mail: morgan.deal@umontpellier.fr
² Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse Cedex 4, France
³ CNRS, IRAP, 14 avenue Edouard Belin, 31400 Toulouse, France

Received: 25 January 2016
Accepted: 8 March 2016

Abstract

Aims. Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to important variations of the chemical composition inside the stars. The accumulation in specific layers of the elements, which are the main contributors of the local opacity, leads to hydrodynamical instabilities that modify the internal stellar structure and surface abundances. Our aim is to study these effects and compare the resulting surface abundances with spectroscopic observations

Methods. We computed the detailed structure of A-type stars including these effects. We used the Toulouse-Geneva Evolution Code (TGEC), where radiative accelerations are computed using the single valued parameter (SVP) method, and we added double-diffusive convection with mixing coefficients deduced from three-dimensional (3D) simulations.

Results. We show that the modification of the initial chemical composition has important effects on the internal stellar mixing and leads to different surface abundances of the elements. The results fit the observed surface chemical composition well if the layers, which are individually mixed by double-diffusive convection, are connected.