Homogeneous abundance analysis of FGK dwarf, subgiant, and giant stars with and without giant planets
Aims: We have analyzed high-resolution and high signal-to-noise-ratio optical spectra of nearby FGK stars with and without detected giant planets in order to homogeneously measure their photospheric parameters, mass, age, and the abundances of volatile (C, N, and O) and refractory (Na, Mg, Si, Ca, Ti, V, Mn, Fe, Ni, Cu, and Ba) elements. Our sample contains 309 stars from the solar neighborhood (up to the distance of 100 pc), out of which 140 are dwarfs, 29 are subgiants, and 140 are giants.
Methods: The photospheric parameters are derived from the equivalent widths of Fe i and Fe ii lines. Masses and ages come from the interpolation in evolutionary tracks and isochrones on the Hertzsprung-Russell diagram. The abundance determination is based on the equivalent widths of selected atomic lines of the refractory elements and on the spectral synthesis of C2, CN, C i, O i, and Na i features. We apply a set of statistical methods to analyze the abundances derived for the three subsamples.
Results: Our results show that: i) giant stars systematically exhibit underabundance in [C/Fe] and overabundance in [N/Fe] and [Na/Fe] in comparison with dwarfs, a result that is normally attributed to evolution-induced mixing processes in the envelope of evolved stars; ii) for solar analogs alone, the abundance trends with the condensation temperature of the elements are correlated with age and anticorrelated with the surface gravity, which agrees with recent studies; iii) as in the case of [Fe/H], dwarf stars with giant planets are systematically enriched in [X/H] for all the analyzed elements, except for O and Ba (the former due to limitations of statistics), confirming previous findings in the literature that it is not only iron that has an important relation with the planetary formation; and iv) giant planet hosts are also significantly overabundant for the same metallicity when the elements from Mg to Cu are combined.