Issue |
A&A
Volume 414, Number 2, February I 2004
|
|
---|---|---|
Page(s) | 633 - 650 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20031594 | |
Published online | 19 January 2004 |
Simulating star formation in molecular cloud cores
I. The influence of low levels of turbulence on fragmentation and multiplicity
Dept. of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff, CF24 3YB, UK
Corresponding author: S. P. Goodwin, simon.goodwin@astro.cf.ac.uk
Received:
21
August
2003
Accepted:
10
October
2003
We present the results of an ensemble of simulations of the collapse
and fragmentation of dense star-forming cores. We show that even with
very low levels of turbulence the outcome is usually a binary, or
higher-order multiple, system.
We take as the initial conditions for these simulations a typical
low-mass core, based on the average properties of a large sample
of observed cores. All the simulated cores start with a mass of
, a flattened central density profile,
a ratio of thermal to gravitational energy
and a ratio of turbulent to gravitational energy
. Even this low level of turbulence – much lower than
in most previous simulations – is sufficient to produce multiple
star formation in 80% of the cores; the mean number of stars and
brown dwarfs formed
from a single core is 4.55, and the maximum is 10. At the outset, the
cores have no large-scale rotation. The only difference between each
individual simulation is the detailed structure of the turbulent
velocity field.
The multiple systems formed in the simulations
have properties consistent with
observed multiple systems. Dynamical evolution tends preferentially to
eject lower mass stars and brown dwarves whilst hardening the
remaining binaries so that the median semi-major axis of binaries formed
is ~30 AU. Ejected objects are usually single low-mass
stars and brown dwarfs, yielding a strong correlation between
mass and multiplicity. Brown dwarves are ejected with a higher average
velocity than stars, and over time this should lead to mass segregation
in the parent cluster. Our simulations suggest a natural mechanism
for forming binary
stars that does not require large-scale rotation, capture,
or large amounts of turbulence.
Key words: stars: formation
© ESO, 2004
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