The atmospheric parameters of the components of the 16 Cygni binary system , in which the secondary has a gas giant planet detected , are measured accurately using high quality observational data .
Abundances relative to solar are obtained for 25 elements with a mean error of \sigma ( \mathrm { [ X / H ] } ) = 0.023 dex .
The fact that \cyga has about four times more lithium than 16 Cyg B is normal considering the slightly different masses of the stars .
The abundance patterns of \cyga and B , relative to iron , are typical of that observed in most of the so-called solar twin stars , with the exception of the heavy elements ( Z > 30 ) , which can , however , be explained by Galactic chemical evolution .
Differential ( A–B ) abundances are measured with even higher precision ( \sigma ( \Delta \mathrm { [ X / H ] } ) = 0.018 dex , on average ) .
We find that \cyga is more metal-rich than 16 Cyg B by \Delta \mathrm { [ M / H ] } = +0.041 \pm 0.007 dex .
On an element-to-element basis , no correlation between the A–B abundance differences and dust condensation temperature ( T _ { \mathrm { C } } ) is detected .
Based on these results , we conclude that if the process of planet formation around 16 Cyg B is responsible for the observed abundance pattern , the formation of gas giants produces a constant downwards shift in the photospheric abundance of metals , without a T _ { \mathrm { C } } correlation .
The latter would be produced by the formation of terrestrial planets instead , as suggested by other recent works on precise elemental abundances .
Nevertheless , a scenario consistent with these observations requires the convective envelopes of \simeq 1 M _ { \odot } stars to reach their present-day sizes about three times quicker than predicted by standard stellar evolution models .