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Testing the universality of star formation – I. Multiplicity in nearby star-forming regions

Authors

  • Robert R. King,

    Corresponding author
    1. Astrophysics Group, College of Engineering Mathematics and Physical Sciences, University of Exeter, Stocker Road, Exeter EX4 4QL
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  • Richard J. Parker,

    1. Institute of Astronomy, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
    2. Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH
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  • Jenny Patience,

    1. Astrophysics Group, College of Engineering Mathematics and Physical Sciences, University of Exeter, Stocker Road, Exeter EX4 4QL
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  • Simon P. Goodwin

    1. Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH
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E-mail: rob@astro.ex.ac.uk

ABSTRACT

We have collated multiplicity data for five clusters (Taurus, Chamaeleon I, Ophiuchus, IC 348 and the Orion Nebula Cluster). We have applied the same mass ratio (flux ratios of ΔK≤ 2.5) and primary mass cuts (0.1–3.0 M) to each cluster and therefore have directly comparable binary statistics for all five clusters in the separation range 62–620 au, and for Taurus, Chamaeleon I and Ophiuchus in the range 18–830 au. We find that the trend of decreasing binary fraction with cluster density is solely due to the high binary fraction of Taurus; the other clusters show no obvious trend over a factor of nearly 20 in density.

With N-body simulations, we attempt to find a set of initial conditions that are able to reproduce the density, morphology and binary fractions of all five clusters. Only an initially clumpy (fractal) distribution with an initial total binary fraction of 73 per cent (17 per cent in the range 62–620 au) is able to reproduce all of the observations (albeit not very satisfactorily). Therefore, if star formation is universal, then the initial conditions must be clumpy and with a high (but not 100 per cent) binary fraction. This could suggest that most stars, including M dwarfs, form in binaries.

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