The Gaia-ESO Survey: Insights on the inner-disc evolution from open
  clusters
  Context. The inner disc, linking the thin disc with the bulge, has been
somehow neglected in the past because of intrinsic difficulties in its study,
due, e.g., to crowding and high extinction. Open clusters located in the inner
disc are among the best tracers of its chemistry at different ages and
distances. Aims. We analyse the chemical patterns of four open clusters located
within 7 kpc of the Galactic Centre and of field stars to infer the properties
of the inner disc with the Gaia-ESO survey idr2/3 data release. Methods. We
derive the parameters of the newly observed cluster, Berkeley 81, finding an
age of about 1 Gyr and a Galactocentric distance of 5.4 kpc. We construct the
chemical patterns of clusters and we compare them with those of field stars in
the Solar neighbourhood and in the inner-disc samples. Results. Comparing the
three populations we observe that inner-disc clusters and field stars are both,
on average, enhanced in [O/Fe], [Mg/Fe] and [Si/Fe]. Using the idr2/3 results
of M67, we estimate the non-local thermodynamic equilibrium (NLTE) effect on
the abundances of Mg and Si in giant stars. After empirically correcting for
NLTE effects, we note that NGC 6705 and Be 81 still have a high [{\alpha}/Fe].
Conclusions. The location of the four open clusters and of the field population
reveals that the evolution of the metallicity [Fe/H] and of [alpha/Fe] can be
explained within the framework of a simple chemical evolution model: both
[Fe/H] and [{\alpha}/Fe] of Trumpler 20 and of NGC 4815 are in agreement with
expectations from a simple chemical evolution model. On the other hand, NGC
6705, and at a lower level Berkeley 81, have higher [{\alpha}/Fe] than expected
for their ages, location in the disc, and metallicity. These differences might
originate from local enrichment processes as explained in the inhomogeneous
evolution framework.
