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

TL;DR

This study investigates how atomic diffusion and radiative accelerations induce hydrodynamical instabilities in A stars, affecting their internal structure and surface element abundances, with results aligning well with spectroscopic observations.

Contribution

It introduces detailed stellar models including atomic diffusion, radiative accelerations, and double-diffusive convection, providing new insights into surface abundance variations in A stars.

Findings

Chemical composition modifications significantly affect internal mixing.

Surface abundances match observations when layers are connected by double-diffusive convection.

Models show the importance of layered mixing in stellar surface composition.

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.