Reipurth, Bo

Contact Email: reipurth@casa.colorado.edu
Institute: CASA, University of Colorado, CB 389, Boulder,
CO 80309
First Coauthor: Cathie Clarke
Institute: Institute of Astronomy, Cambridge, UK
Subject Area: Brown Dwarfs & Extrasolar Planets
Waveband: Multi-wavelength
Technique: Computational Astrophysics
Presentation: Oral Contribution: Tuesday
Title: The Expulsion of Brown Dwarfs from Disintegrating Multiple Systems
Abstract: A recent analysis of the multiplicity of 14 sources driving giant Herbig-Haro flows has revealed an observed binary frequency between 79% and 86%, of which half are higher-order multiples. These sources represent the hitherto youngest sample of stars examined for binarity. The much lower binarity and multiplicity frequency on the main sequence suggests that significant dynamical evolution takes place after the birth of a multiple system. Disintegration of a triple or higher-order system is a stochastic process that can occur early or late in the evolution of the system, and can be described only in terms of the half-life of the decay. A stellar embryo competes with its siblings in order to accrete infalling matter, and the one that grows slowest is most likely to be ejected. Brown dwarfs may be substellar objects because they have been expelled from small newborn multiple systems which have decayed in dynamical interactions. In this view, brown dwarfs are stellar embryos for which the star formation process was aborted before the hydrostatic cores could build up enough mass to eventually start hydrogen burning. With better luck, a brown dwarf would therefore have become a normal star. This interpretation of brown dwarfs readily explains the rarity of brown dwarfs as close companions to normal stars, the absence of wide brown dwarf binaries, and the flattening of the low mass end of the initial mass function. Possible observational tests of this scenario include statistics of brown dwarfs near Class 0 sources, and the kinematics of brown dwarfs in star forming regions while they still retain a kinematic signature of their expulsion. Because the ejection process limits the amount of gas brought along in a disk, it is predicted that substellar equivalents to the classical T Tauri stars are not common. Catastrophic decay events punctuating the star forming process may provide important new insights to our understanding of early stellar evolution.