The Gaia-ESO Survey: Probes of the inner disk abundance gradient
  The nature of the metallicity gradient inside the solar circle (R_GC < 8 kpc)
is poorly understood, but studies of Cepheids and a small sample of open
clusters suggest that it steepens in the inner disk. We investigate the
metallicity gradient of the inner disk using a sample of inner disk open
clusters that is three times larger than has previously been studied in the
literature to better characterize the gradient in this part of the disk. We
used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars
in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H]
values were determined based on a membership analysis for each cluster. Where
necessary, distances and ages to clusters were determined via comparison to
theoretical isochrones. The GES open clusters exhibit a radial metallicity
gradient of -0.10+-0.02 dex/kpc, consistent with the gradient measured by other
literature studies of field red giant stars and open clusters in the range R_GC
~ 6-12 kpc. We also measure a trend of increasing [Fe/H] with increasing
cluster age, as has also been found in the literature. We find no evidence for
a steepening of the inner disk metallicity gradient inside the solar circle as
earlier studies indicated. The age-metallicity relation shown by the clusters
is consistent with that predicted by chemical evolution models that include the
effects of radial migration, but a more detailed comparison between cluster
observations and models would be premature.
