Planet accretion and the abundances of lithium isotopes

Abstract

Planet accretion onto solar type stars may significantly change the stellar atmospheric abundances of 6Li and 7Li if it takes place after the star has arrived at the main sequence. Ingestion of planets at an earlier phase will not affect theses abundances because of extensive pre-main sequence mixing and burning. We present quantitative estimates of the main sequence evolution of stellar surface lithium abundances after planet ingestion. At solar metallicities, for stellar masses in the range ∼1.3-1.1 M⊙, a large fraction of the ingested 6Li is likely to be preserved during the whole main sequence lifetime according to the standard model. Preservation of the less fragile 7Li isotope occurs in a larger mass range ∼1.3-0.9 M⊙, At high metallicities typical of planet host stars, the ranges of masses are slightly reduced essentially due to the thicker convective zones. Further reduction is expected if non-standard processes cause extra-mixing of material below the base of the convective zone, but even in this case there are stellar masses where both isotopes are significantly preserved. We conclude that there is a range of stellar effective temperature where migration and accretion of planets and planetary material can be empirically tested using high-resolution spectroscopy of the lithium isotopes.