On the metallicity distribution of classical Cepheids in the Galactic
  inner disk
  We present homogeneous and accurate iron abundances for almost four dozen
(47) of Galactic Cepheids using high-spectral resolution (R$\sim$40,000) high
signal-to-noise ratio (S/N $\ge$ 100) optical spectra collected with UVES at
VLT. A significant fraction of the sample (32) is located in the inner disk (RG
$le$ 6.9 kpc) and for half of them we provide new iron abundances. Current
findings indicate a steady increase in iron abundance when approaching the
innermost regions of the thin disk. The metallicity is super-solar and ranges
from 0.2 dex for RG $\sim$ 6.5 kpc to 0.4 dex for RG $\sim$ 5.5 kpc. Moreover,
we do not find evidence of correlation between iron abundance and distance from
the Galactic plane. We collected similar data available in the literature and
ended up with a sample of 420 Cepheids. Current data suggest that the mean
metallicity and the metallicity dispersion in the four quadrants of the
Galactic disk attain similar values. The first-second quadrants show a more
extended metal-poor tail, while the third-fourth quadrants show a more extended
metal-rich tail, but the bulk of the sample is at solar iron abundance.
Finally, we found a significant difference between the iron abundance of
Cepheids located close to the edge of the inner disk ([Fe/H]$\sim$0.4) and
young stars located either along the Galactic bar or in the nuclear bulge
([Fe/H]$\sim$0). Thus suggesting that the above regions have had different
chemical enrichment histories. The same outcome applies to the metallicity
gradient of the Galactic bulge, since mounting empirical evidence indicates
that the mean metallicity increases when moving from the outer to the inner
bulge regions.
