  Studies suggest that the pollution of white dwarf (WD) atmospheres arises
from the accretion of minor planets, but the exact properties of polluting
material, and in particular the evidence for water in some cases are not yet
understood. Previous works studied the water retention in minor planets around
main-sequence and evolving host stars, in order to evaluate the possibility
that water survives inside minor planets around WDs. However, all of these
studies focused on small, comet-sized to moonlet-sized minor planets, when the
inferred mass inside the convection zones of He-dominated WDs could actually
also be compatible with much more massive minor planets. In this study we
therefore explore for the first time, the water retention inside exo-planetary
dwarf planets, or moderate-sized moons, with radii of the order of hundreds of
kilometres. We now cover nearly the entire potential mass range of minor
planets. The rest of the parameter space considered in this study is identical
to that of our previous study, and also includes multiple WD progenitor star
masses. We find that water retention in more massive minor planets is still
affected by the mass of the WD progenitor, however not as much as when small
minor planets were considered. We also find that water retention is now almost
always greater than zero. On average, the detected water fraction in
He-dominated WD atmospheres should be at least 5\%, irrespective of the assumed
initial water composition, if it came from a single accretion event of an icy
dwarf planet or moon. This finding also strengthens the possibility of WD
habitability. To finalize our previous and current findings, we provide a code
which may be freely used as a service to the community. The code calculates ice
and water retention by interpolation, spanning the full mass range of both
minor planets and their host stars.
