GEPI

We present homogeneous and accurate iron abundances for 130 Galactic Cepheids based on high–spectral resolution (R∼ 38,000) high signal-to-noise ratio (SNR ≥ 100) optical spectra collected with UVES at VLT. The above abundances were complemented with high–quality iron abundances available in the literature. We paid attention in deriving a homogeneous metallicity scale and ended up with a sample of 450 Cepheids. We also estimated for the entire sample accurate individual distances by using homogeneous near-infrared (NIR) photometry and the reddening free Period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (RG ∼5–20 kpc) and agrees quite well with similar estimates available in the literature(-0.060±0.002 dex/kpc). We also uncover evidence which suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid Groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers H II regions, OB associations and open clusters. We found very similar metallicity gradients for ages younger than 3 Gyrs, while for older ages we found a shallower slope and an increase in the intrinsic spread. We also present preliminary results concerning alpha-element gradients. We found that they agree, within the errors, with the iron gradient.