Spatial differences between stars and brown dwarfs: a dynamical origin?

Parker, Richard J. ; Andersen, Morten

In: Monthly Notices of the Royal Astronomical Society, 2014, vol. 441, no. 1, p. 784-789

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    We use N-body simulations to compare the evolution of spatial distributions of stars and brown dwarfs in young star-forming regions. We use three different diagnostics: the ratio of stars to brown dwarfs as a function of distance from the region's centre, $\mathcal {R}_{\rm SSR}$, the local surface density of stars compared to brown dwarfs, ΣLDR, and we compare the global spatial distributions using the ΛMSR method. From a suite of 20 initially statistically identical simulations, 6/20 attain $\mathcal {R}_{\rm SSR} \ll 1$ and ΣLDR≪1 and ΛMSR≪1, indicating that dynamical interactions could be responsible for observed differences in the spatial distributions of stars and brown dwarfs in star-forming regions. However, many simulations also display apparently contradictory results - for example, in some cases the brown dwarfs have much lower local densities than stars (ΣLDR≪1), but their global spatial distributions are indistinguishable (ΛMSR=1) and the relative proportion of stars and brown dwarfs remains constant across the region ($\mathcal {R}_{\rm SSR} = 1$). Our results suggest that extreme caution should be exercised when interpreting any observed difference in the spatial distribution of stars and brown dwarfs, and that a much larger observational sample of regions/clusters (with complete mass functions) is necessary to investigate whether or not brown dwarfs form through similar mechanisms to stars