The impact of stellar companion UV photons on the chemistry of the
  circumstellar environments of AGB stars
  Spherical asymmetries are prevalent within the outflows of AGB stars. Since
binary interaction with a stellar or planetary companion is thought to be the
underlying mechanism behind large-scale structures, we included the effects of
UV radiation originating from a stellar companion in our chemical kinetics
model. The one-dimensional model provides a first approximation of its effects
on the chemistry throughout the outflow. The presence of a close-by stellar
companion can strongly influence the chemistry within the entire outflow. Its
impact depends on the intensity of the radiation (set by the stellar radius and
blackbody temperature) and on the extinction the UV radiation experiences (set
by the outflow density, density structure, and assumed radius of dust
formation). Parent species can be photodissociated by the companion, initiating
a rich photon-driven chemistry in the inner parts of the outflow. The outcome
depends on the balance between two-body reactions and photoreactions. If
two-body reactions dominate, chemical complexity within the outflow increases.
This can make the abundance profiles of daughters appear like those of parents,
with a larger inner abundance and a gaussian decline. If photoreactions
dominate, the outflow can appear molecule-poor. We model three stellar
companions. The impact of a red dwarf companion is limited. Solar-like
companions show the largest effect, followed by a white dwarf. A stellar
companion can also lead to the formation of unexpected species. The outflow's
molecular content, especially combined with abundance profiles, can indicate a
stellar companion's presence. Our results pave the way for further
outflow-specific (three-dimensional) model development.
