Magneto-convective models of red dwarfs: constraints imposed by the lithium abundance

TL;DR

This study uses magneto-convective models to explore how magnetic fields influence lithium depletion in low-mass stars, providing insights into their internal magnetic structures and their effects on stellar evolution.

Contribution

It introduces magneto-convective models constrained by empirical data to analyze lithium abundance and magnetic fields in specific low-mass stars, highlighting differences in magnetic field origins.

Findings

YY Gem's magnetic field is consistent with a dynamo origin.

CU Cnc's lithium abundance suggests a magnetic field too strong for a typical dynamo.

Models successfully match observed stellar parameters and lithium levels.

Abstract

Magnetic fields impede the onset of convection, thereby altering the thermal structure of a convective envelope in a low mass star: this has an effect on the amount of lithium depletion in a magnetized star. In order to quantify this effect, we have applied a magneto-convective model to two low mass stars for which lithium abundances and precise structural parameters are known: YY Gem and CU Cnc. For both stars, we have obtained models which satisfy empirical constraints on the following parameters: R, L, surface magnetic field strength, and Li abundance. In the case of YY Gem, we have obtained a model which satisfies the empirical constraints with an internal magnetic field of several megagauss: such a field strength is within the range of a dynamo where the field energy is in equipartition with rotational energy deep inside the convection zone. However, in the case of CU Cnc, the Li requires an internal magnetic field which is probably too strong for a dynamo origin: we suggest possible alternatives which might account for the reported Li abundance in CU Cnc.