The evolution of the Milky Way: New insights from open clusters
  We have collected high-dispersion echelle spectra of red giant members in the
twelve open clusters (OCs) and derived stellar parameters and chemical
abundances for 26 species by either line equivalent widths or synthetic
spectrum analyses. We confirm the lack of an age-metallicity relation for OCs
but argue that such a lack of trend for OCs arise from the limited coverage in
metallicity compared to that of field stars which span a wide range in
metallicity and age. We confirm that the radial metallicity gradient of OCs is
steeper (flatter) for Rgc < 12 kpc (> 12 kpc). We demonstrate that the sample
of clusters constituting a steep radial metallicity gradient of slope
$-$0.052$\pm$0.011 dex kpc$^{-1}$ at Rgc < 12 kpc are younger than 1.5 Gyr and
located close to the Galactic midplane (|z| < 0.5 kpc) with kinematics typical
of the thin disc. Whereas the clusters describing a shallow slope of
$-$0.015$\pm$0.007 dex kpc$^{-1}$ at Rgc > 12 kpc are relatively old, thick
disc members with a striking spread in age and height above the midplane (0.5 <
|z| < 2.5 kpc). Our investigation reveals that the OCs and field stars yield
consistent radial metallicity gradients if the comparison is limited to samples
drawn from the similar vertical heights. We argue via the computation of
Galactic orbits that all the outer disc clusters were actually born inward of
12 kpc but the orbital eccentricity has taken them to present locations very
far from their birthplaces.
