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Brown dwarf formation by binary disruption

 Goodwin, S. P. and Whitworth, Anthony Peter 2007. Brown dwarf formation by binary disruption. Astronomy & Astrophysics 466 (3) , pp. 943-948. 10.1051/0004-6361:20066745

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Abstract

Context.The principal mechanism by which brown dwarfs form, and its relation to the formation of higher-mass (i.e. hydrogen-burning) stars, is poorly understood. Aims.We advocate a new model for the formation of brown dwarfs. Methods.In this model, brown dwarfs are initially binary companions, formed by gravitational fragmentation of the outer parts ( $R\ga 100\,{\rm AU}$) of protostellar discs around low-mass hydrogen-burning stars. Most of these binaries are then gently disrupted by passing stars to create a largely single population of brown dwarfs and low-mass hydrogen-burning stars. Results.This idea is consistent with the excess of binaries found in low-density pre-main sequence populations, like that in Taurus, where they should survive longer than in denser clusters. Conclusions.If brown dwarfs form in this way, as companions to more massive stars, the difficulty of forming very low-mass prestellar cores is avoided. Since the disrupted binaries will tend to be those involving low-mass components and wide orbits, and since disruption will be due to the gentle tides of passing stars (rather than violent N-body interactions in small-N sub-clusters), the liberated brown dwarfs will have velocity dispersions and spatial distributions very similar to higher-mass stars, and they will be able to retain discs, and thereby to sustain accretion and outflows. Thus the problems associated with the ejection and turbulence mechanisms can be avoided. This model implies that most, possibly all, stars and brown dwarfs form in binary or multiple systems.

Item Type: Article Publication Published Physics and Astronomy Q Science > QB Astronomy stars: formation -- stars: binaries: general -- stars: low-mass, brown dwarfs Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/0004-6361/ (accessed 16/04/2014) EDP Sciences 0004-6361 30 March 2016 04 Jun 2017 04:54 http://orca-mwe.cf.ac.uk/id/eprint/46343