Constraints on the properties of macroscopic transport in the Sun from combined lithium and beryllium depletion

TL;DR

This study uses lithium and beryllium depletion data to constrain the properties of macroscopic transport processes in the Sun, revealing limitations of current models and the need for improved understanding of internal mixing mechanisms.

Contribution

It provides new constraints on the efficiency and extent of macroscopic mixing below the solar convective envelope based on recent abundance measurements.

Findings

Power law density dependence with index 3-6 fits the data

Macroscopic mixing efficiency around 6000 cm²/s at the convective base

Current magnetic Tayler instability models do not match observations

Abstract

Context. The Sun is a privileged laboratory of stellar evolution, thanks to the quality and complementary nature of available constraints. Using these observations, we are able to draw a detailed picture of its internal structure and dynamics which form the basis of the successes of solar modelling. Amongst such constraints, the depletion of lithium and beryllium are key tracers of the required efficiency and extent of macroscopic mixing just below the solar convective envelope. Thanks to revised determinations of these abundances, we may use them in conjunction with other existing spectroscopic and helioseismic constraints to study in detail the properties of macroscopic transport. Aims. We aim at constraining the efficiency of macroscopic transport at the base of the convective envelope and determining the compatibility of the observations with a suggested candidate linked with the transport of angular momentum in the solar radiative interior. Methods. We use recent spectroscopic observations of lithium and beryllium abundance and include them in solar evolutionary model calibrations. We test the agreement of such models in terms of position of the convective envelope, helium mass fraction in convective zone, sound speed profile inversions and neutrino fluxes. Results. We constrain the required efficiency and extent of the macroscopic mixing at the base of the solar convective envelope, finding that a power law of density with an index n between 3 and 6 would reproduce the data, with efficiencies at the base of the envelope of about 6000 cm2 /s, depending on the value of n. We also confirm that macroscopic mixing worsens the agreement with neutrino fluxes and that the current implementations of the magnetic Tayler instability are unable to explain the observations.