Volume 420, Number 1, June II 2004
|Page(s)||183 - 205|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||14 May 2004|
The Nearest 15 pc
McDonald Observatory and Department of Astronomy, University of Texas, Austin, TX 78712-1083, USA e-mail: email@example.com
2 Uppsala Astronomical Observatory, Box 515, 751-20 Uppsala, Sweden e-mail: firstname.lastname@example.org
3 Observatório Nacional, Rua General José Cristino 77 CEP 20921-400, Rio de Janeiro, Brazil e-mail: email@example.com
Corresponding author: C. Allende Prieto, firstname.lastname@example.org
Accepted: 3 March 2004
We report the results of a high-resolution spectroscopic survey of all the stars more luminous than MV = 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 , continuous spectral coverage between nm, and typical signal-to-noise ratios in the range . 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.
Key words: surveys / stars: fundamental parameters / stars: abundances / Galaxy: solar neighbourhood
Based on observations made with the 2.7 m telescope at the McDonald Observatory of the University of Texas at Austin (Texas), and the 1.52 m telescope at the European Southern Observatory (La Silla, Chile) under the agreement with the CNPq/Observatorio Nacional (Brazil).
© ESO, 2004
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