Effect of episodic accretion on the structure and the lithium depletion of low-mass stars and planet-hosting stars

摘要

Following up our recent analysis devoted to the impact of nonsteady accretion on the location of young low-mass stars or browndwarfs in the Herzsprung-Russell diagram, we perform a detailedanalysis devoted to the effect of burst accretion on the internalstructure of low-mass and solar type stars. We find that episodicaccretion can produce objects with significantly higher centraltemperatures than the onesof the non accreting counterparts of same mass and age. As aconsequence, lithium depletion can be severely enhanced in theseobjects.This provides a natural explanation for the unexpected level of lithiumdepletion observed in young objects for the inferred age of theirparent cluster. These results confirm the limited reliability oflithium abundance as a criterion for assessing or rejecting clustermembership. They also show that lithium is not a reliable ageindicator, because its fate strongly depends on the past accretionhistory of the star. Under the assumption that giant planets primarilyform in massive disks prone to gravitational instability and thus toaccretion burst episodes, the same analysis also explains the higher Lidepletion observed in planet hosting stars. At last, we show that,depending on the burst rate and intensity, accretion outbursts canproduce solar mass stars with lower convective envelope masses, at agesless than a few tens of Myr, than predicted by standard (non or slowlyaccreting) pre-main sequence models. This result has interesting,although speculative, implications for the recently discovereddepletion of refractory elements in the Sun. Key words: stars: formation - stars: low-mass - stars: abundances - accretion, accretion disks