|Authors||Pavel Kroupa1,2, Jérôme Bouvier1, Gaspard Duchêne3, Estelle Moraux1|
|Affiliation||1 Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, F-38041 Grenoble Cedex 9, France |
2 Institut für Theoretische Physik und Astrophysik der Universität Kiel, D-24098 Kiel, Germany
3Department of Physics and Astronomy, 405 Hilgard Avenue, UCLA, Los Angeles, CA 90095-1562, USA
|Accepted by||Monthly Notices of the Royal Astronomical Society|
The models produce a very high initial binary proportion among stars (SM), and stars and BDs (SMwBDs), and both reproduce the measured initial mass function (IMF) in TA, the ONC and the Pleiades as well as the Galactic field. Concentrating on the SMwBDs, it is shown that the Briceno et al. result that TA appears to have produced significantly fewer BDs per star than the ONC is reproduced almost exactly without calling for a different IMF. The reason is that star--BD and BD--BD binaries are disrupted in the dense ONC. The model, however, fails to reproduce the observed star--star binary period distribution in TA, because it contains too many star--BD pairs. Also, the SMwBDs leads to too many wide star--BD and BD--BD systems. This is a problem if most stars form in clusters because Galactic-field very-low-mass-star and BD binaries have a low binary fraction and do not contain wide systems. The SM, on the other hand, finds excellent agreement with the observed mass-ratio and period distribution among TA and Galactic-field stellar binaries, as well as the observed stellar period distribution in the ONC and the Pleiades.
The conclusion of this work is therefore that the SM describes the initial, dynamically unevolved stellar population very well indeed for a large range of star-forming conditions, suggesting (1) a remarkable invariance of the star-formation products, and (2) that BDs (and some very-low-mass stars) need to be added as a separate population with its own kinematical and binary properties. This separate population may vary with star-forming conditions.