New insights in the origin and evolution of the old, metal-rich open
  cluster NGC 6791
  NGC 6791 is one of the most studied open clusters, it is massive
($\sim5000\,M_{\odot}$), located at the solar circle, old ($~8\,$Gyr) and yet
the most metal-rich cluster (${\rm [Fe/H]}\simeq0.4$) known in the Milky Way.
By performing an orbital analysis within a Galactic model including spiral arms
and a bar, we found that it is plausible that NGC 6791 formed in the inner thin
disc or in the bulge, and later displaced by radial migration to its current
orbit. We apply different tools to simulate NGC 6791, including direct $N$-body
summation in time-varying potentials, to test its survivability when going
through different Galactic environments. In order to survive the 8 Gyr journey
moving on a migrating orbit, NGC 6791 must have been more massive, $M_0 \geq
5\times10^4 M_{\odot}$, when formed. We find independent confirmation of this
initial mass in the stellar mass function, which is observed to be flat; this
can only be explained if the average tidal field strength experienced by the
cluster is stronger than what it is at its current orbit. Therefore, the birth
place and journeys of NGC 6791 are imprinted in its chemical composition, in
its mass loss, and in its flat stellar mass function, supporting its origin in
the inner thin disc or in the bulge.
