Binary star formation and the outflows from their discs

Kuruwita, R. L., Federrath, C., Ireland, M. J., 2017

Monthly Notices of the Royal Astronomical Society, 470, 1626  [ ADS link ]  [ PDF ]


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%, ~33%, ~42% of the respective quantities in the single star case). The tight binary's efficiency falls between the other two cases (~71%, ~66%, ~87% 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.

The following animation shows side-on gas density projections of the single star (left), the tight binary (middle) and the wide binary (right). Crosses show the position of the stars. The thin lines show the magnetic field, and the arrows indicate the velocity field. The mass accreted by the stars is indicated on the bottom left of each panel.


binary_jets_xz.mp4, 23MB high-res mp4 ]

This movie shows a zoomed-in top-down view of the discs.


binary_jets_xy.mp4, 23MB high-res mp4 ]


We thank the anonymous referee for the constructive feedback and comments that helped to improve the paper. R.K. would like to thank the Australian Government for the financial support provided by the Australian Postgraduate Award. C.F. gratefully acknowledges funding provided by the Australian Research Council's Discovery Projects (grants DP150104329 and DP170100603). The simulations presented in this work used high performance computing resources provided by the Leibniz Rechenzentrum and the Gauss Centre for Supercomputing (grants pr32lo, pr48pi and GCS Large-scale project 10391), the Partnership for Advanced Computing in Europe (PRACE grant pr89mu), the Australian National Computational Infrastructure (grant ek9), and the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia, in the framework of the National Computational Merit Allocation Scheme and the ANU Allocation Scheme. The simulation software FLASH was in part developed by the DOE-supported Flash Center for Computational Science at the University of Chicago.

© C. Federrath 2018