  The origin of R Coronae Borealis stars has been elusive for over 200 years.
Currently, two theories for their formation have been presented. These are the
Final Flash scenario, in which a dying asymptotic giant branch (AGB) star
throws off its atmosphere to reveal the hydrogen poor, heavily processed
material underneath, and the double degenerate scenario, in which two white
dwarfs merge to produce a new star with renewed vigour. Some theories predict
that the temperatures reached during the latter scenario would destroy any
lithium originally present in the white dwarfs. The observed lithium content of
some R Coronae Borealis stars, therefore, is often interpreted as an indication
that the Final Flash scenario best describes their formation. In this paper, it
is shown that lithium production can, indeed, occur in the merging of a helium
white dwarf with a carbon-oxygen white dwarf if their chemical composition,
particularly that of 3He, is fully considered. The production mechanism is
described in detail, and the sensitivity of lithium production to the merger
environment is investigated. Nucleosynthesis post-processing calculations of
smoothed-particle hydrodynamics (SPH) tracer particles are performed to show
that any lithium produced in these environments will be concentrated towards
the cloud of material surrounding the R CrB star. Measurements of the lithium
content of these clouds would, therefore, provide a valuable insight into the
formation mechanism of R CrB stars.
