Issue |
A&A
Volume 423, Number 1, August III 2004
|
|
---|---|---|
Page(s) | 169 - 182 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20040285 | |
Published online | 29 July 2004 |
Simulating star formation in molecular cores
II. The effects of different levels of turbulence
Dept. of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3YB, UK e-mail: Simon.Goodwin@astro.cf.ac.uk
Received:
17
February
2004
Accepted:
1
May
2004
We explore, by means of a large ensemble of SPH simulations, how the level
of turbulence affects the collapse and fragmentation of a star-forming core.
All our simulated cores have the same mass (),
the same initial density profile (chosen to fit observations of L1544),
and the same barotropic equation of state, but we vary (a) the initial
level of turbulence (as measured by the ratio of turbulent to gravitational
energy,
) and (b), for fixed
, the
details of the initial turbulent velocity field (so as to obtain good
statistics).
A low level of turbulence (
)
suffices to produce multiple systems, and as
is increased,
the number of objects formed and the companion frequency both increase. The mass
function is bimodal, with a flat low-mass segment representing single objects
ejected from the core before they can accrete much, and a Gaussian high-mass
segment representing objects which because they remain in the core grow
by accretion and tend to pair up in multiple systems.
The binary statistics reported for field G-dwarfs by Duquennoy
& Mayor ([CITE], A&A, 248, 485) are only reproduced with
. For
much lower values of
(
0.025), insufficient binaries
are formed. For higher values of
(
0.10), there
is a significant sub-population of binaries with small semi-major axis
and large mass-ratio (i.e. close binaries with
components of comparable mass). This sub-population is not present in
Duquennoy & Mayor's sample, although there is some evidence for it in
the pre-Main Sequence population of Taurus analyzed by White & Ghez ([CITE], ApJ, 556, 265).
It arises because with larger
, more low-mass objects
are formed, and so there is more scope for the binaries remaining in the
core to be hardened by ejecting these low-mass objects. Hard binaries thus
formed then tend to grow towards comparable mass by competitive accretion
of material with relatively high specific angular momentum.
Key words: methods: numerical / stellar dynamics / stars: formation / ISM: general
© ESO, 2004
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