The effect of binding energy and resolution in simulations of the common envelope binary interaction

Abstract

The common envelope binary interaction remains one of the least understood\nphases in the evolution of compact binaries, including those that result in\nType Ia supernovae and in mergers that emit detectable gravitational waves. In\nthis work we continue the detailed and systematic analysis of 3D hydrodynamic\nsimulations of the common envelope interaction aimed at understanding the\nreliability of the results. Our first set of simulations replicate the 5\nsimulations of Passy et al. (a 0.88Msun, 90Rsun RGB primary with companions in\nthe range 0.1 to 0.9Msun) using a new AMR gravity solver implemented on our\nmodified version of the hydrodynamic code Enzo. Despite smaller final\nseparations obtained, these more resolved simulations do not alter the nature\nof the conclusions that are drawn. We also carry out 5 identical simulations\nbut with a 2.0Msun primary RGB star with the same core mass as the Passy et al.\nsimulations, isolating the effect of the envelope binding energy. With a more\nbound envelope all the companions in-spiral faster and deeper though relatively\nless gas is unbound. Even at the highest resolution, the final separation\nattained by simulations with a heavier primary is similar to the size of the\nsmoothed potential even if we account for the loss of some angular momentum by\nthe simulation. As a result we suggest that a ~2.0$Msun RGB primary may\npossibly end in a merger with companions as massive as 0.6Msun, something that\nwould not be deduced using analytical arguments based on energy conservation.\n