A&A 375, 989-998 (2001)
DOI: 10.1051/0004-6361:20010915
The formation and evolution of binary systems
III. Low-mass binaries in the Praesepe cluster
J. Bouvier1, G. Duchêne1, 2, J.-C. Mermilliod3 and T. Simon41 Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France http://www-laog.obs.ujf-grenoble.fr/
2 UCLA Division of Astronomy and Astrophysics, Los Angeles, CA 90095-1562, USA
3 Institut d'Astronomie de l'Université de Lausanne, 1290 Chavannes-des-Bois, Switzerland
4 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
(Received 3 April 2001 / Accepted 22 June 2001 )
Abstract
With the aim of investigating the binary population of the
700 Myr old Praesepe cluster, we have observed 149 G and K-type cluster
members using adaptive optics. We detected 26 binary systems with an
angular separation ranging from less than 0.08 to 3.3 arcsec (15-600 AU). After correcting for detection biases, we derive
a binary frequency
(BF) in the 
(days) range from 4.4 to 6.9 of
% , which
is similar to that of field G-type dwarfs (23.8% , Duquennoy & Mayor
1991). This result, complemented by similar ones obtained for the 2 Myr
old star forming cluster IC 348 (Paper II) and the 120 Myr old Pleiades
open cluster (Paper I), indicates that the fraction of long-period
binaries does not
significantly evolve over the lifetime of galactic open clusters.
We compare the distribution of cluster binaries to the binary populations
of star forming regions, most notably Orion and Taurus, to critically
review current ideas regarding the binary formation process. We conclude
that it is still unclear whether the lower binary fraction observed in
young clusters compared to T associations is purely the result of the
early dynamical disruption of primordial binaries in dense clusters or
whether it reflects intrinsically different modes of star formation in
clusters and associations. We also note that if Taurus binaries result
from the dynamical decay of small-N protostellar aggregates, one would
predict the existence of a yet to be found dispersed population
of mostly single substellar objects in the Taurus cloud.
Key words: stars: binaries: close -- stars: formation -- stars: low-mass, brown dwarfs -- galaxy: open clusters and associations: individual: Praesepe, M 44
Offprint request: J. Bouvier, jbouvier@laog.obs.ujf-grenoble.fr
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