With the aim of connecting the compositions of stars and planets , we present the abundances of carbon and oxygen , as well as iron and nickel , for the transiting exoplanet host star XO-2N and its wide-separation binary companion XO-2S .
Stellar parameters are derived from high-resolution , high-signal-to-noise spectra , and the two stars are found to be similar in their T _ { eff } , log g , iron ( [ Fe/H ] ) , nickel ( [ Ni/H ] ) abundances .
Their carbon ( [ C/H ] ) and oxygen ( [ O/H ] ) abundances also overlap within errors , although XO-2N may be slightly more C-rich and O-rich than XO-2S .
The C/O ratios of both stars ( \sim 0.60 \pm 0.20 ) may also be somewhat larger than solar ( C/O \sim 0.50 ) .
The XO-2 system has a transiting hot Jupiter orbiting one binary component but not the other , allowing us to probe the potential effects planet formation might have on the host star composition .
Additionally , with multiple observations of its atmosphere the transiting exoplanet XO-2b lends itself to compositional analysis , which can be compared to the natal chemical environment established by our binary star elemental abundances .
This work sets the stage for determining how similar/different exoplanet and host star compositions are , and the implications for planet formation , by discussing the C/O ratio measurements in the unique environment of a visual binary system with one star hosting a transiting hot Jupiter .