High Precision Abundances in the 16 Cyg Binary System: A Signature of the Rocky Core in the Giant Planet
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We study the stars of the binary system 16 Cygni to determine with high precision their chemical composition. Knowing that the component B has a detected planet of at least 1.5 Jupiter masses, we investigate if there are chemical peculiarities that could be attributed to planet Formation around this star. We perform a differential abundance analysis using high resolution (R = 81,000) and high S/N (similar to 700) CFHT/ESPaDOnS spectra of the 16 Cygni stars and the Sun; the latter was obtained from light reflected of asteroids. We determine differential abundances of the binary components relative to the Sun and between components A and B as well. We achieve a precision of sigma less than or similar to 0.005 dex and a total error similar to 0.01 dex for most elements. The effective temperatures and surface gravities found for 16 Cyg A and B are T-eff = 5830 +/- 7 K, log g = 4.30 +/- 0.02 dex, and T-eff = 5751 +/- 6K, log g = 4.35 +/- 0.02 dex, respectively. The component 16 Cyg A has ametallicity ([Fe/H]) higher by 0.047 +/- 0.005 dex than 16 Cyg B, as well as a microturbulence velocity higher by 0.08 km s(-1). All elements show abundance differences between the binary components, but while the volatile difference is about 0.03 dex, the refractories differ by more and show a trend with condensation temperature, which could be interpreted as the signature of the rocky accretion core of the giant planet 16 Cyg Bb. We estimate a mass of about 1.5-6 M-circle times for this rocky core, in good agreement with estimates of Jupiter's core.