Lithium depletion in solar-like stars: effect of overshooting based on realistic multi-dimensional simulations
Astrophysical Journal Letters
American Astronomical Society / IOP Publishing
© 2017. The American Astronomical Society. All rights reserved.
We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from $\sim$ 50 Myr to $\sim$ 4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long standing problem of lithium depletion in pre-main sequence and main sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.
This work is funded by the ERC grant No. 320478-TOFU. It used the DiRAC Complexity system which is part of the STFC DiRAC HPC Facility (funded by BIS National E-Infrastructure capital grant ST/K000373/1 and Operations grant ST/K0003259/1). This work also used the University of Exeter Supercomputer ISCA.
This is the final version of the article. Available from American Astronomical Society via the DOI in this record.
Vol. 845 (1), article L6