  Post-asymptotic giant branch (post-AGB) binaries are surrounded by massive
disks of gas and dust that are similar to protoplanetary disks around young
stars. We assembled a catalog of all known Galactic post-AGB binaries with
disks. We explore the correlations between the different observables with the
aim of learning more about potential disk-binary interactions. We compiled
spectral energy distributions of 85 Galactic post-AGB binary systems. We built
a color-color diagram to differentiate between the different disk morphologies
traced by the infrared excess. We categorized the different disk types and
searched for correlations with other observational characteristics of these
systems. Between 8 and 12% of our targets are surrounded by transition disks,
that is, disks having no or low near-infrared excess. We find a strong link
between these transition disks and the depletion of refractory elements on the
surface of the post-AGB star. We interpret this link as evidence of a mechanism
that stimulates the dust and gas separation within the disk and that also
produces the transition disk structure. We propose that such a mechanism is
likely to be due to a giant planet carving a hole in the disk, effectively
trapping the dust in the outer disk parts. We propose disk evolutionary
scenarios, depending on the presence of such a giant planet in the disk. We
advocate that giant planets can successfully explain the link between the
transition disks and the observed depletion of refractory materials. If the
planetary scenario is confirmed, disks around post-AGB binaries could be a
unique laboratory for testing planet-disk interactions and their influence on
the late evolution of binary stars. The question of whether such planets are
first- or second-generation bodies remains to be considered. We argue that
these disks are ideal for studying planet formation in unprecedented parameter
space.

Earth and Planetary Astrophysics;Solar and Stellar Astrophysics