Differences Between Stars and Brown Dwarfs

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

Authors:

Parker et al

Abstract:

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, 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 twenty initially statistically identical simulations, 6/20 attain SSR much less 1 and ΣLDR much less 1 and ΛMSR much less 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 much less 1), but their global spatial distributions are indistinguishable (ΛMSR=1) and the relative proportion of stars and brown dwarfs remains constant across the region (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.