  We aim to study the dust distribution in the central regions of the Keplerian
disk of the Red Rectangle, the prototype of binary post-AGB stars with rotating
circumbinary disks, and to compare it with the distribution of relevant
molecular gas tracers
  We present new high-resolution (20 milliarcseconds, mas) ALMA observations of
continuum and line emissions at 0.9 mm. The maps have been analyzed by means of
a simple model of dust and free-free emissionn that is able to reproduce the
continuum data.
  Resuts: i) We find that most of the dust emission in the Red Rectangle is
concentrated in the inner disk regions, with a typical size of 250 AU in
diameter and 50 AU in width. ii) The settlement of dust grains onto inner
equatorial regions is remarkable when compared with the relatively widespread
gas distribution. iii) This region is basically coincident with the warm PDR
(photo-dominated region) where CI, CII, and certain molecules such as HCN are
presumably formed, as well as probably PAHs (polycyclic aromatic hydrocarbons,
whose emission is very strong in this source). iv) We confirm the large size of
the grains, with a typical radius ~ 150 mu The opacity of dust at 0.9 mm is
deduced to be relatively large, ~0.5. v) We also confirm the existence of a
very compact HII region in the center, for which we measure an extent of 10 -
15 mas (~ 10 AU) and a total flux of 7 - 8 mJy at 0.9 mm.
