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Description
Using high-quality spectra of the twin stars in the XO-2 binary system, we have detected significant differences in the chemical composition of their photospheres. The differences correlate strongly with the elements' dust condensation temperature. In XO-2N, volatiles are enhanced by about 0.015dex and refractories are overabundant by up to 0.090dex. On average, our error bar in relative abundance is 0.012dex. We present an early metal-depletion scenario in which the formation of the gas giant planets known to exist around these stars are responsible for a 0.015 dex offset in the abundances of all elements while 20M_{Earth}_ of non-detected rocky objects that formed around XO-2S explain the additional refractory-element difference. An alternative explanation involves the late accretion of at least 20M_{Earth}_of planet-like material by XO-2N, allegedly as a result of the migration of the hot Jupiter detected around that star. Dust cleansing by a nearby hot star as well as age or Galactic birthplace effects can be ruled out as valid explanations for this phenomenon.
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