The Gaia-ESO Survey: Lithium depletion in the Gamma Velorum cluster and inflated radii in low-mass pre-main-sequence stars

TL;DR

This study reveals that accounting for radius inflation in low-mass pre-main-sequence stars resolves discrepancies between observed lithium depletion patterns and color-magnitude diagrams, suggesting stars are older and larger than previously modeled.

Contribution

It introduces the concept that radius inflation due to magnetic activity explains lithium depletion and CMD observations in young clusters, revising stellar age and mass estimates.

Findings

Radius inflation of ~10% explains lithium depletion patterns.

Stars are at least twice as old as non-magnetic models suggest.

Incorporating magnetic effects alters stellar mass and temperature estimates.

Abstract

We show that non-magnetic models for the evolution of pre-main-sequence (PMS) stars *cannot* simultaneously describe the colour-magnitude diagram (CMD) and the pattern of lithium depletion seen in the cluster of young, low-mass stars surrounding $\gamma^2$ Velorum. The age of 7.5+/-1 Myr inferred from the CMD is much younger than that implied by the strong Li depletion seen in the cluster M-dwarfs and the Li depletion occurs at much redder colours than predicted. The epoch at which a star of a given mass depletes its Li and the surface temperature of that star are both dependent on its radius. We demonstrate that if the low-mass stars have radii ~10 per cent larger at a given mass and age, then both the CMD and Li depletion pattern of the Gamma Vel cluster are explained at a common age of 18-21 Myr. This radius inflation could be produced by some combination of magnetic suppression of convection and extensive cool starspots. Models that incorporate radius inflation suggest that PMS stars similar to those in the Gamma Vel cluster, in the range 0.2<M/Msun<0.7, are at least a factor of two older and ~7 per cent cooler than previously thought and that their masses are much larger (by >30 per cent) than inferred from conventional, non-magnetic models in the Hertzsprung-Russell diagram. Systematic changes of this size may be of great importance in understanding the evolution of young stars, disc lifetimes and the formation of planetary systems.