Brown dwarf formation by binary disruption

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 > 100 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.

6 pages, no figures. Accepted for A&A

References in corpus (10)

• Stellar Multiplicity and the IMF: Most Stars Are Single
• A SCUBA survey of Orion, the low-mass end of the core mass function
• Exploring brown dwarf disks: A 1.3 mm survey in Taurus
• The minimum mass for star formation, and the origin of binary brown dwarfs
• A search for binary systems among the nearest L dwarfs
• Rotation and accretion of very low mass objects in the SigmaOri cluster
• A Survey for Spectroscopic Binaries Among Very Low-Mass Stars
• The Spatial Distribution of Brown Dwarfs in Taurus
• Multiplicity and Optical Excess Across the Substellar Boundary in Taurus
• Five new very low mass binaries

Cited by in corpus (9)

• Theory of Star Formation
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• The Stellar Population of the Chamaeleon I Star-Forming Region
• Gravitational fragmentation and the formation of brown dwarfs in stellar clusters
• Dense Stellar Populations: Initial Conditions
• The relationship between the prestellar core mass function and the stellar initial mass function
• Binary frequency of very young brown dwarfs at separations smaller than 3 AU
• The influence of multiple stars on the high-mass stellar initial mass function and age-dating of young massive star clusters
• A discontinuity in the low-mass IMF - the case of high multiplicity