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

¹ STAR Institute, Université de Liège, Liège, Belgium
² Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516 751 20 Uppsala, Sweden
³ University of Virginia, Astronomy Building, 530 McCormick Road, PO Box 400325 Charlottesville, VA 22904, USA
⁴ LUPM, Université de Montpellier, CNRS, Place Eugène Bataillon, 34095 Montpellier, France
⁵ Centre Spatial de Liège, Université de Liège, Angleur-Liège, Belgium

^⋆ Corresponding author; gbuldgen@uliege.be

Received: 7 November 2024
Accepted: 6 January 2025

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 forms the basis of the successes of solar modelling. Amongst such observations, constraints on 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 to constrain the efficiency of macroscopic transport at the base of the solar convective zone (BCZ) 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 the 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 BCZ, finding that a power-law density with an index, n, between 3 and 6 would reproduce the data, with efficiencies at the BCZ 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.