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Description
We want to investigate how planet formation is imprinted on stellar surface composition using up-to-date stellar evolution models. We simulate the evolution of pre-main-sequence stars as a function of the efficiency of heat injection during accretion, the deuterium mass fraction, and the stellar mass, M*. For simplicity, we assume that planet formation leads to the late accretion of zero-metallicity gas, diluting the surface stellar composition as a function of the mass of the stellar outer convective zone. We estimate that in the solar system, between 97 and 168 Mearth of condensates formed planets or were ejected from the system. We adopt 150 M_earth_(M*/M_sun_)(Z/Z_sun_) as an uncertain but plausible estimate of the mass of heavy elements that is not accreted by stars with giant planets, including our Sun. By combining our stellar evolution models to these estimates, we evaluate the consequences of planet formation on stellar surface compositions. We show that after the first ~0.1 million years (Myr) during which stellar structure can differ widely from the usually assumed fully-convective structure, the evolution of the convective zone follows classical pre-main-sequence evolutionary tracks within a factor of two in age. We find that planet formation should lead to a scatter in stellar surface composition that is larger for high-mass stars than for low-mass stars. We predict a spread in [Fe/H] of approximately 0.05dex for stars of temperature Teff~6500K, to 0.02dex for Teff~5500K, marginally compatible with differences in metallicities observed in some binary stars with planets. Stars with Teff>=7000K may show much larger [Fe/H] deficits, by 0.6dex or more, in the presence of efficient planet formation, compatible with the existence of refractory-poor lambda Boo stars. We also find that planet formation may explain the lack of refractory elements seen in the Sun as compared to solar twins, but only if the ice-to-rock ratio in the solar-system planets is less than ~0.4 and planet formation began less than ~1.3Myr after the beginning of the formation of the Sun.
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