The contribution of binary star formation via core-fragmentation on protostellar multiplicity
Rajika Kuruwita
Thursday, Dec. 8th, 9:00CET
Observations of young multiple star systems find a bimodal distribution in companion frequency and separation. Using simulations of star formation in giant molecular clouds we investigate the influence of environment on multiple star formation pathways and the contribution of core-fragmentation is on the formation of close <100au binaries. Simulations are run with the adaptive mesh refinement code RAMSES with sufficient resolution to resolve core-fragmentation beyond 400au and dynamical evolution down to 16au, but without the possibility of resolving disc-fragmentation. The evolution of the resulting stellar systems is followed over millions of years. We find that star formation in lower gas density environments is more clustered, but despite this, the fractions of systems that form via dynamical capture and core-fragmentation are broadly consistent at 40\% and 60\% respectively. In all gas density environments, we find the typical scale at which systems form via core-fragmentation is 103−3.5au. After formation, we find that systems that form via core-fragmentation have slightly lower inspiral rates (∼10−1.75au/yr measured over first 10000yr) compared to dynamical capture (∼10−1.25au/yr). We then compared the simulation with conditions most similar to the Perseus star forming region to determine whether the bimodal distribution observed by Tobin et al. (2016) can be replicated. We find that it can be replicated, but it is sensitive to the evolutionary state of the simulation. Our results indicate that a significant number of binary star systems with separations <100au can be produced via non-disc-fragmentation pathways due to efficient inspiral, suggesting disc-fragmentation is not the dominant formation pathway for low-mass close binaries in nature.