Abstract details

We analyze a sample of about 3000 stars extracted from the Sloan Digital Sky Survey (SDSS-DR5) with Teff in the range 4750-7000 K and log g greater than 1.5 dex. For these objects atmospheric parameter estimates are obtained by comparing observed and synthetic spectral indices. The latter are derived from an "ad hoc" library of synthetic spectra computed either with Solar-Scaled (SSA grid) or alpha-enhanced Abundances (NSSA grid). The models and the synthetic spectra are at fixed [Fe/H]=+0.5, +0.2, +0.0, -0.5, -1.0, -1.5, -2.0, and -2.5 with [alpha/Fe]=+0.0 and +0.4. Distances are derived by using the evolutionary tracks by Girardi et al.(2004). The dependence of the alpha-enhancement phenomenon on stellar metallicity and on galactic position is investigated.