S⁴N: A spectroscopic survey of stars in the solar neighborhood: The nearest 15 pc

We report the results of a high-resolution spectroscopic survey of all the stars more luminous than M_v = 6.5 mag within 14.5 pc from the Sun. The Hipparcos catalog's completeness limits guarantee that our survey is comprehensive and free from some of the selection effects in other samples of nearby stars. The resulting spectroscopic database, which we have made publicly available, includes spectra for 118 stars obtained with a resolving power of R ≃ 50 000, continuous spectral coverage between ∼362-921 nm, and typical signal-to-noise ratios in the range 150-600. We derive stellar parameters and perform a preliminary abundance and kinematic analysis of the F-G-K stars in the sample. The inferred metallicity ([Fe/H]) distribution is centered at about -0.1 dex, and shows a standard deviation of 0.2 dex. A comparison with larger samples of Hipparcos stars, some of which have been part of previous abundance studies, suggests that our limited sample is representative of a larger volume of the local thin disk. We identify a number of metal-rich K-type stars which appear to be very old, confirming the claims for the existence of such stars in the solar neighborhood. With atmospheric effective temperatures and gravities derived independently of the spectra, we find that our classical LTE model-atmosphere analysis of metal-rich (and mainly K-type) stars provides discrepant abundances from neutral and ionized lines of several metals. This ionization imbalance could be a sign of departures from LTE or inhomogeneous structure, which are ignored in the interpretation of the spectra. Alternatively, but seemingly unlikely, the mismatch could be explained by systematic errors in the scale of effective temperatures. Based on transitions of majority species, we discuss abundances of 16 chemical elements. In agreement with earlier studies we find that the abundance ratios to iron of Si, Sc, Ti, Co, and Zn become smaller as the iron abundance increases until approaching the solar values, but the trends reverse for higher iron abundances. At any given metallicity, stars with a low galactic rotational velocity tend to have high abundances of Mg, Si, Ca, Sc, Ti, Co, Zn, and Eu, but low abundances of Ba, Ce, and Nd. The Sun appears deficient by roughly 0.1 dex in O, Si, Ca, Sc, Ti, Y, Ce, Nd, and Eu, compared to its immediate neighbors with similar iron abundances.