First metallicity determination from Near-Infrared spectra for five
  obscured Cepheids discovered in the inner Disk
  We report the discovery from our IRSF/SIRIUS Near-Infrared (NIR) variability
survey of five new classical Cepheids located in the inner Galactic Disk, at
longitude $l\simeq -40^{\circ}$. The new Cepheids are unique in probing the
kinematics and metallicity of young stars at the transition between the inner
Disk and the minor axis of the central Bar, where they are expected to be less
affected by its dynamical influence.This is also the first time that
metallicity of Cepheids is estimated on the basis of medium-resolution
($R\sim3,000$) NIR spectra, and we validated our results with data in the
literature, finding a minimal dependence on the adopted spectroscopic
diagnostics. This result is very promising for using Cepheids as stellar proxy
of the present-time chemical content of the obscured regions in the Disk. We
found that the three Cepheids within 8--10 kpc from us have metallicities
consistent with the mean radial metallicity gradient, and kinematics consistent
with the Galactic rotation curve. Instead, the closest ($\sim$4 kpc)/farthest
($\sim$12 kpc) Cepheids have significant negative/positive residuals, both in
velocity and in iron content. We discuss the possibility that such residuals
are related to large-scale dynamical instabilities, induced by the
bar/spiral-arm pattern, but the current sample is too limited to reach firm
conclusions.
