ZERO IMPACT PARAMETER WHITE DWARF COLLISIONS IN FLASH

We systematically explore zero impact parameter collisions of white dwarfs (WDs) with the Eulerian adaptive grid code FLASH for 0.64 + 0.64 M-circle dot and 0.81 + 0.81 M-circle dot mass pairings. Our models span a range of effective linear spatial resolutions from 5.2 x 10(7) to 1.2 x 10(7) cm. However, even the highest resolution models do not quite achieve strict numerical convergence, due to the challenge of properly resolving small-scale burning and energy transport. The lack of strict numerical convergence from these idealized configurations suggests that quantitative predictions of the ejected elemental abundances that are generated by binary WD collision and merger simulations should be viewed with caution. Nevertheless, the convergence trends do allow some patterns to be discerned. We find that the 0.64 + 0.64 M-circle dot head-on collision model produces 0.32 M-circle dot of Ni-56 and 0.38 M-circle dot of Si-28, while the 0.81 + 0.81 M-circle dot head-on collision model produces 0.39 M-circle dot of Ni-56 and 0.55 M-circle dot of Si-28 at the highest spatial resolutions. Both mass pairings produce similar to 0.2 M-circle dot of unburned C-12+O-16. We also find the 0.64 + 0.64 M-circle dot head-on collision begins carbon burning in the central region of the stalled shock between the two WDs, while the more energetic 0.81 + 0.81 M-circle dot head-on collision raises the initial post-shock temperature enough to burn the entire stalled shock region to nuclear statistical equilibrium.