Fundamental parameters for 45 open clusters with Gaia DR2, an improved
  extinction correction and a metallicity gradient prior
  Reliable fundamental parameters of open clusters such as distance, age and
extinction are key to our understanding of Galactic structure and stellar
evolution. In this work we use {\it Gaia} DR2 to investigate 45 open clusters
listed in the \emph{New catalogue of optically visible open clusters and
candidates} (DAML) but with no previous astrometric membership estimation based
on {\it Gaia} DR2. In the process of selecting targets for this study we found
that some clusters reported as new discoveries in recent papers based on {\it
Gaia} DR2 were already known clusters listed in DAML. Cluster memberships were
determined using a maximum likelihood method applied to {\it Gaia} DR2
astrometry. This has allowed us to estimate mean proper motions and mean
parallaxes for all investigated clusters. Mean radial velocities were also
determined for 12 clusters, 7 of which had no previous published values. We
have improved our isochrone fitting code to account for interstellar extinction
using an updated extinction polynomial for the {\it Gaia} DR2 photometric
band-passes and the Galactic abundance gradient as a prior for metallicity. The
updated procedure was validated with a sample of clusters with high quality
$[Fe/H]$ determinations. We then did a critical review of the literature and
verified that our cluster parameter determinations represent a substantial
improvement over previous values.
