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 ( \sim 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 \lesssim 0.005 dex and a total error \sim 0.01 dex for most elements .
The effective temperatures and surface gravities found for 16 Cyg A and B are T _ { eff } = 5830 \pm 7 K , \log g = 4.30 \pm 0.02 dex , and T _ { eff } = 5751 \pm 6 K , \log g = 4.35 \pm 0.02 dex , respectively .
The component 16 Cyg A has a metallicity ( \mathrm { [ Fe / H ] } ) higher by 0.047 \pm 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 _ { \earth } for this rocky core , in good agreement with estimates of Jupiter ’ s core .