Nearby stars of the Galactic disk and halo

Model atmosphere analyses of echelle spectra of some fifty nearby F- and G-type stars are presented. The sample is confined to the main-sequence, turnoff and subgiant region, regardless of the metal abundance. On the base of these data, spectroscopic parallaxes are calculated and compared to the Hipparcos astrometry to explore the reliability of the derived stellar parameters, notably the surface gravity and metal abundance scale. The spectroscopic distance scale is found in good agreement with the Hipparcos parallaxes and is characterized by a 5% rms uncertainty. The results suggest a precision in log g of ~ 0.1 dex, and 0.05-0.10 dex for the metallicity. There is also reasonable evidence for the spectroscopic effective temperature scale to be free of systematic errors; typical uncertainties are assessed to ~ 80 K. The basic spectroscopic parameters are supplemented by data for the microturbulence velocities, the projected rotational velocities, stellar radii and alpha -enhancement abundances, the latter represented by the element magnesium. Stellar masses are also given, though many are probably subject to small adjustments (typically 5%) in forthcoming analyses. The well-defined distance correlation is also demonstrated to be an efficient means for an identification of spectroscopic binaries. The results are discussed in terms of a spectroscopically established distance scale, the sites of the stellar populations in the [Mg/H]-[Fe/Mg] plane, a timescale for the Galactic thin disk, and the potential of future T_eff-log g Kiel diagrams for a precise determination of Galactic globular clusters ages. Based on observations at the German Spanish Astronomical Center, Calar Alto, Spain.