Metal-rich accretion and thermohaline instabilities in exoplanets-host stars: consequences on the light elements abundances

TL;DR

This paper investigates how metal-rich accretion events and thermohaline instabilities affect the surface composition and light element abundances in exoplanet-host stars, combining modeling, analysis, and observational implications.

Contribution

It provides a comprehensive model of thermohaline mixing due to metal-rich accretion and discusses its impact on stellar surface abundances, integrating recent numerical simulations.

Findings

Thermohaline mixing dilutes metal excess in stellar surfaces.

Light element abundances can trace past accretion events.

Consistent treatment of thermohaline convection aligns with recent simulations.

Abstract

The early evolution of planetary systems is expected to depend on various periods of disk matter accretion onto the central star, which may include the accretion of metal-rich matter after the star settles on the main sequence. When this happens, the accreted material is rapidly mixed within the surface convective zone and induces an inverse mean-molecular-weight gradient, unstable for thermohaline convection. The induced mixing, which dilutes the metal excess, may also have important consequences on the light elements abundances. We model and analyze this process, and present the results according to various possible accretion scenarios. We give a detailed discussion of the different ways of treating thermohaline mixing, as proposed by previous authors, and we converge on a consistent view, including the most recent numerical simulations. We show how the observations of light elements in stars can be used as tracers of such events.