POSSIBLE STELLAR METALLICITY ENHANCEMENTS FROM THE ACCRETION OF PLANETS

A number of recently discovered extrasolar planet candidates have surp risingly small orbits, which may indicate that considerable orbital mi gration takes place in protoplanetary systems. A natural consequence o f orbital migration is for a series of planets to be accreted, destroy ed, and then thoroughly mixed into the convective envelope of the cent ral star: We study the ramifications of planet accretion for the final main-sequence metallicity of the star. If maximum disk lifetimes are on the order of similar to 10 Myr, stars with masses near 1.0 M-circle dot are predicted to have virtually no metallicity enhancement. On th e other hand, early F-and late A-type stars with masses M- approximat e to 1.5-2.0 M circle dot can experience significant metallicity enhan cements due to their considerably smaller convection zones during the first 10 Myr of pre-main-sequence evolution. We show that the metallic ities of an aggregate of unevolved F stars are consistent with an aver age star accreting similar to 2 Jupiter-mass planets from a protoplane tary disk having a 10 Myr dispersal time.