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A high precision chemical abundance analysis of the HAT-P-1 stellar binary: constraints on planet formation

We present a high-precision, differential elemental abundance analysis of the HAT-P-1 stellar binary based on high-resolution, high signal-to-noise ratio Keck/HIRES spectra. The secondary star in this double system is known to host a transiting giant planet while no planets have yet been detected around the primary star. The derived metallicities ([Fe/H]) of the primary and secondary stars are identical within the errors: $0.146 \pm 0.014$ dex ($σ$ = 0.033 dex) and $0.155 \pm 0.007$ dex ($σ$ = 0.023 dex), respectively. Extremely precise differential abundance ratios of 23 elements have been measured (mean error of $σ$([X/Fe]) = 0.013 dex) and are found to be indistinguishable between the two stars: $Δ$[X/Fe] (secondary - primary) = $+0.001 \pm 0.006$ dex ($σ$ = 0.008 dex). The striking similarity in the chemical composition of the two stellar components in HAT-P-1 is contrary to the possible 0.04 dex level difference seen in 16 Cyg A+B, which also hosts a giant planet, at least 3 times more massive than the one around HAT-P-1 secondary star. We conclude that the presence of giant planets does not necessarily imply differences in the chemical compositions of the host stars. The elemental abundances of each star in HAT-P-1 relative to the Sun show an identical, positive correlation with the condensation temperature of the elements; their abundance patterns are thus very similar to those observed in the majority of solar twins. In view of the Melendez et al. (2009)'s interpretation of the peculiar solar abundance pattern, we conclude that HAT-P-1 experienced less efficient formation of terrestrial planets than the Sun. This is in line with the expectation that the presence of close-in giant planets preventing the formation or survival of terrestrial planets.