Non-Zero Impact Parameter White Dwarf Collisions in FLASH

We systematically explore non-zero impact parameter collisions of white dwarfs with the Eulerian adaptive grid code FLASH for 0.64+0.64 Msun and 0.81+0.81 Msun mass pairings. For both mass pairings, we use two impact parameters, b=1 (one white dwarf radius from center to center at the time of collision), and b=2 (two white dwarf radii from center to center at the time of collision). Our models span a range of effective linear spatial resolutions from 6.25E7 to 1.37E7 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 suggest that quantitative predictions of the ejected elemental abundances that are generated by binary white dwarf 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 Msun b=1 collision model produces 0.0562 Msun of Ni-56 and 0.494 Msun of Si-28, while the 0.81+0.81 Msun b=1 collision model produces 0.100 Msun of Ni-56 and 0.656 Msun of Si-28 at the highest spatial resolutions. Both mass pairings produce ~0.3 Msun of unburned C-12+O-16. For the b=2 case, neither mass pairing produces a significant amount of Ni-56 due to the relatively slow process of merging.