Binary star formation and the outflows from their discs

Abstract

We carry out magnetohydrodynamical simulations with flash of the formation of a single, a tight binary (a ∼ 2.5 au) and a wide binary star (a ∼ 45 au). We study the outflows and jets from these systems to understand the contributions the circumstellar and circumbinary discs have on the efficiency and morphology of the outflow. In the single star and tight binary case, we obtain a single pair of jets launched from the system, while in the wide binary case, two pairs of jets are observed. This implies that in the tight binary case, the contribution of the circumbinary disc on the outflow is greater than that in the wide binary case. We also find that the single star case is the most efficient at transporting mass, linear and angular momentum from the system, while the wide binary case is less efficient ( ∼ 50 per cent, ∼ 33 per cent, ∼ 42 per cent of the respective quantities in the single star case). The tight binary's efficiency falls between the other two cases ( ∼ 71 per cent, ∼66 per cent, ∼87 per cent of the respective quantities in the single star case). By studying the magnetic field structure, we deduce that the outflows in the single star and tight binary star case are magnetocentrifugally driven, whereas in the wide binary star case, the outflows are driven by a magnetic pressure gradient.