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Title:
Simulating star formation in molecular cores. II. The effects of different levels of turbulence
Authors:
Goodwin, S. P.; Whitworth, A. P.; Ward-Thompson, D.
Affiliation:
AA(Department of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3YB, UK ), AB(Department of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3YB, UK), AC(Department of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3YB, UK)
Publication:
Astronomy and Astrophysics, v.423, p.169-182 (2004) (A&A Homepage)
Publication Date:
08/2004
Origin:
A&A
Astronomy Keywords:
methods: numerical, stellar dynamics, stars: formation, ISM: general
DOI:
10.1051/0004-6361:20040285
Bibliographic Code:
2004A&A...423..169G

Abstract

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 (5.4 M⊙), 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, αturb ≡ Uturb/|Ω| = 0, 0.01, 0.025, 0.05, 0.10;and;0.25) and (b), for fixed αturb, the details of the initial turbulent velocity field (so as to obtain good statistics).

A low level of turbulence (αturb ˜ 0.05) suffices to produce multiple systems, and as αturb 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{Duquennoy91}, A&A, 248, 485) are only reproduced with αturb ˜ 0.05. For much lower values of αturb (⪉ 0.025), insufficient binaries are formed. For higher values of αturb (⪆ 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{White01}, ApJ, 556, 265). It arises because with larger αturb, 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.

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