Possible Stellar Metallicity Enhancements from the Accretion of Planets

A number of recently discovered extrasolar planet candidates havesurprisingly small orbits, which may indicate that considerable orbitalmigration takes place in protoplanetary systems. A natural consequence oforbital migration is for a series of planets to be accreted, destroyed, andthen thoroughly mixed into the convective envelope of the central star. Westudy the ramifications of planet accretion for the final main sequencemetallicity of the star. If maximum disk lifetimes are on the order of 10 Myr,stars with masses near 1 solar mass are predicted to have virtually nometallicity enhancement. On the other hand, early F and late A type stars withmasses of 1.5--2.0 solar masses can experience significant metallicityenhancements due to their considerably smaller convection zones during thefirst 10 Myr of pre-main-sequence evolution. We show that the metallicities ofan aggregate of unevolved F stars are consistent with an average star accretingabout 2 Jupiter-mass planets from a protoplanetary disk having a 10 Myrdispersal time.Comment: 14 pages, AAS LaTeX, 3 figures, accepted to ApJ Letter