  We study the properties of double white dwarf (DWD) mergers by performing
hydrodynamic simulations using the new and improved adaptive mesh refinement
code Octo-Tiger. We follow the orbital evolution of DWD systems of mass ratio
q=0.7 for tens of orbits until and after the merger to investigate them as a
possible origin for R Coronae Borealis (RCB) type stars. We reproduce previous
results, finding that during the merger, the Helium WD donor star is tidally
disrupted within 20-80 minutes since the beginning of the simulation onto the
accretor Carbon-Oxygen WD, creating a high temperature shell around the
accretor. We investigate the possible Helium burning in this shell and the
merged object's general structure. Specifically, we are interested in the
amount of Oxygen-16 dredged-up to the hot shell and the amount of Oxygen-18
produced. This is critical as the discovery of very low Oxygen-16 to Oxygen-18
ratios in RCB stars pointed out the merger scenario as a favorable explanation
for their origin. A small amount of hydrogen in the donor may help keep the
Oxygen-16 to Oxygen-18 ratios within observational bounds, even if moderate
dredge-up from the accretor occurs. In addition, we perform a resolution study
to reconcile the difference found in the amount of Oxygen-16 dredge-up between
smoothed-particle hydrodynamics and grid-based simulations.
