154 research outputs found
The Origin of the Initial Mass Function
We review recent advances in our understanding of the origin of the initial
mass function (IMF). We emphasize the use of numerical simulations to
investigate how each physical process involved in star formation affects the
resulting IMF. We stress that it is insufficient to just reproduce the IMF, but
that any successful model needs to account for the many observed properties of
star forming regions including clustering, mass segregation and binarity.
Fragmentation involving the interplay of gravity, turbulence, and thermal
effects is probably responsible for setting the characteristic stellar mass.
Low-mass stars and brown dwarfs can form through the fragmentation of dense
filaments and disks, possibly followed by early ejection from these dense
environments which truncates their growth in mass. Higher-mass stars and the
Salpeter-like slope of the IMF are most likely formed through continued
accretion in a clustered environment. The effects of feedback and magnetic
fields on the origin of the IMF are still largely unclear. Lastly, we discuss a
number of outstanding problems that need to be addressed in order to develop a
complete theory for the origin of the IMF.Comment: PPV conference paper, 16 pages, 11 figur
PPV Chapter - The Formation of Brown Dwarfs
We review five mechanisms for forming brown dwarfs: (i) turbulent
fragmentation of molecular clouds, producing very low-mass prestellar cores by
shock compression; (ii) collapse and fragmentation of more massive prestellar
cores; (iii) disc fragmentation; (iv) premature ejection of protostellar
embryos from their natal cores; and (v) photo-erosion of pre-existing cores
overrun by HII regions. These mechanisms are not mutually exclusive. Their
relative importance probably depends on environment, and should be judged by
their ability to reproduce the brown-dwarf IMF, the distribution and kinematics
of newly formed brown dwarfs, the binary statistics of brown dwarfs, the
ability of brown dwarfs to retain discs, and hence their ability to sustain
accretion and outflows. This will require more sophisticated numerical
modelling than is presently possible, in particular more realistic initial
conditions and more realistic treatments of radiation transport, angular
momentum transport and magnetic fields. We discuss the minimum mass for brown
dwarfs, and how brown dwarfs should be distinguished from planets.Comment: 18 pages,3 figures, chapter in Protostars and Planets
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