Paper detail

Homogeneous photospheric parameters and C abundances in G and K nearby stars with and without planets

We present a determination of photospheric parameters and C abundances for a sample of 172 G and K dwarfs, subgiants, and giants with and without detected planets in the solar neighbourhood. The analysis was based on high S/N and high resolution spectra observed with the ELODIE spectrograph, and for which the observational data was publicly available. We intend to contribute precise and homogeneous C abundances in studies that compare the behaviour of light elements in stars, hosting planets or not. This will bring new arguments to the discussion of possible anomalies that have been suggested and will contribute to a better understanding of different planetary formation process. The photospheric parameters were computed through the excitation potential, equivalent widths, and ionisation equilibrium of Fe lines selected in the spectra. C abundances were derived from spectral synthesis applied to prominent molecular head bands of C_2 Swan (5128 and 5165) and to a C atomic line (5380.3). The distribution of [C/Fe] vs. [Fe/H] shows no difference in the behaviour of planet-host stars in comparison with stars for which no planet was detected, for both dwarf and giant subsamples. This result is in agreement with the hypothesis of primordial origin for the chemical abundances presently observed instead of self-enrichment during the planetary system formation and evolution. Additionally, giants are clearly depleted in [C/Fe] (~0.14 dex) when compared with dwarfs, which is probably related to evolution-induced mixing of H-burning products in the envelope of evolved stars. Subgiants, although in small number, seems to follow the same C abundance distribution as dwarfs. We also analysed the kinematics of the sample stars that, in majority, are members of the Galaxy's thin disc. Finally, comparisons with other analogue studies were performed and, within the uncertainties, showed good agreement.