Wide binaries in Planetary Nebulae with Gaia DR2
  Gaia Data Release 2 (DR2) was used to select a sample of 211 central stars of
planetary nebulae (CSPNe) with good quality astrometric measurements, that we
refer to as GAPN, Golden Astrometry Planetary Nebulae. Gaia astrometric and
photometric measurements allowed us to derive accurate distances and radii, and
to calculate luminosities with the addition of self-consistent literature
values. Such information was used to plot the position of these stars in a
Hertzsprung-Russel (HR) diagram and to study their evolutionary status in
comparison with CSPNe evolutionary tracks.
  The extremely precise measurement of parallaxes and proper motions in Gaia
DR2 has allowed us to search for wide binary companions in a region close to
each of the central stars in the GAPN sample. We limited our search to a region
around 20,000 AU of each CSPN to minimise accidental detections, and only
considered stars with good parallax and proper motions data, i.e. with errors
below 30% in DR2. We determined that the hypothetical binary pairs should show
a statistically significant agreement for the three astrometric quantities,
i.e. parallax and both components of proper motions.
  We found 8 wide binary systems among our GAPN sample. One of them is in a
triple system. We compiled the astrometric and photometric measurements of
these binary systems and discussed them in comparison with previously published
searches for binaries in PNe. By analysing the position in the HR diagram of
the companion stars using Gaia photometry, we are able to estimatetheir
temperatures, luminosities, masses and, for one star, the evolutionary age. The
derived quantities yield a consistent scenario when compared with the
corresponding values as obtained for the central stars using stellar
evolutionary models in the postAGB phase.
