Journal Article

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

Robert R. King, Richard J. Parker, Jenny Patience and Simon P. Goodwin

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 3, pages 2025-2042
Published in print April 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20437.x
Testing the universality of star formation – I. Multiplicity in nearby star-forming regions

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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.

Keywords: methods: numerical; binaries: general; stars: formation; stars: kinematics and dynamics; open clusters and associations: general

Journal Article.  11941 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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