OCCASO II. Physical parameters and Fe abundances of Red Clump stars in
  18 Open Clusters
  Open Clusters have long been used to study the chemo-dynamical evolution of
the Galactic disk. This requires an homogeneously analysed sample covering a
wide range of ages and distances. In this aper we present the OCCASO second
data release. This comprises a sample of high-resolution ($R>65,000$) and high
signal-to-noise spectra of 115 Red Clump stars in 18 Open Clusters. We derive
atmospheric parameters ($T_{\mathrm{eff}}$, $\log g$, $\xi$), and [Fe/H]
abundances using two analysis techniques: equivalent widths and spectral
synthesis. A detailed comparison and a critical review of the results of the
two methods are made. Both methods are carefully tested between them, with the
\emph{Gaia} FGK Benchmark stars, and with an extensive sample of literature
values. We perform a membership study using radial velocities and the resulting
abundances. Finally, we compare our results with a chemo-dynamical model of the
Milky Way thin disk concluding that the oldest Open Clusters are consistent
with the models only when dynamical effects are taken into account.
