Structure and dynamics of the inner nebula around the symbiotic stellar
  system R Aqr
  We investigate the structure, dynamics, and chemistry of the molecule-rich
nebula around the stellar symbiotic system R Aqr, which is significantly
affected by the presence of a white dwarf (WD) companion. We study the effects
of the strong dynamical interaction between the AGB wind and the WD and of
photodissociation by the WD UV radiation on the circumstellar shells.
  We obtained high-quality ALMA maps of the 12CO J=2-1, J=3-2, and J=6-5 lines
and of 13CO J=3-2. The maps were analyzed by means of a heuristic 3D model that
is able to reproduce the observations. In order to interpret this description
of the molecule-rich nebula, we performed sophisticated calculations of
hydrodynamical interaction and photoinduced chemistry.
  We find that the CO-emitting gas is distributed within a relatively small
region <~ 1.5". Its structure consists of a central dense component plus
strongly disrupted outer regions, which seem to be parts of spiral arms that
are highly focused on the orbital plane. The structure and dynamics of these
spiral arms are compatible with our hydrodynamical calculations. We argue that
the observed nebula is the result of the dynamical interaction between the wind
and the gravitational attraction of the WD. We also find that UV emission from
the hot companion efficiently photodissociates molecules except in the densest
and best-shielded regions, that is, in the close surroundings of the AGB star
and some shreds of the spiral arms from which the detected lines come. We can
offer a faithful description of the distribution of nebular gas in this
prototypical source, which will be a useful template for studying material
around other tight binary systems.
