Simulations of star formation in Ophiuchus - II. Multiplicity

Abstract

Lomax et al. have constructed an ensemble of 60 pre-stellar cores having masses, sizes, projected shapes, temperatures, and non-thermal radial velocity dispersions that match, statistically, the cores in Ophiuchus, and have simulated the evolution of these cores using smoothed particle hydrodynamics. Each core has been evolved once with no radiative feedback from stars, once with continuous radiative feedback, and once with episodic radiative feedback. Here we analyse the multiplicity statistics from these simulations. With episodic radiative feedback, (i) the multiplicity frequency is ∼60 per cent higher than in the field; (ii) the multiplicity frequency and the mean semimajor axis both increase with primary mass; (iii) one-third of multiple systems are hierarchical systems with more than two components; (iv) in these hierarchical systems the inner pairings typically have separations of a few au and mass ratios concentrated towards unity, whereas the outer pairings have separations of order 100 au and a flatter distribution of mass ratios. The binary statistics are compatible with observations of young embedded populations, and – if wider orbits are disrupted preferentially by external perturbations – with observations of mature field populations. With no radiative feedback, the results are similar to those from simulations with episodic feedback. With continuous radiative feedback, brown dwarfs are underproduced, the number of multiple systems is too low, and the statistical properties of multiple systems are at variance with observation. This suggests that star formation in Ophiuchus may only be representative of global star formation if accretion on to protostars, and hence radiative feedback, is episodic.