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A&A 427, 651-665 (2004)
DOI: 10.1051/0004-6361:20041209
Multiple protostellar systems
I. A deep near infrared survey of Taurus and Ophiuchus protostellar objects
G. Duchêne1, 2, J. Bouvier2, S. Bontemps3, P. André4 and F. Motte41 Department of Physics & Astronomy, UCLA, Los Angeles, CA 90095-1562, USA
2 Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
e-mail: gaspard.duchene@obs.ujf-grenoble.fr
3 Observatoire de Bordeaux, BP 89, 33270 Floirac, France
4 CEA/DSM/DAPNIA, Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
(Received 1 May 2004 / Accepted 21 July 2004)
Abstract
We performed a deep infrared imaging survey of 63 embedded young stellar objects (YSOs) located in the Taurus and Ophiuchus
clouds to search for companions. The sample
includes Class I and flat infrared spectrum protostellar
objects. We find 17 companions physically bound to 15 YSOs
with angular separations in the range 0.8-10´´
(110-1400 AU) and derive a companion star fraction of
23
9% and 29
7% for embedded YSOs in Taurus and
Ophiuchus, respectively, about twice as large as that found
among G dwarfs in the solar neighborhood. Therefore, binary
and multiple protostellar systems are a very frequent
outcome of the fragmentation of prestellar cores. In spite
of different properties of the clouds and especially of the
prestellar cores, the fraction of wide companions,
27
6% for the combined sample, is identical in the
two star-forming regions. This suggests that the frequency
and properties of wide multiple protostellar systems are
not very sensitive to specific initial
conditions. Comparing the companion star fraction of the
youngest YSOs still surrounded by extended envelopes to
that of more evolved YSOs, we find evidence for a possible
evolution of the fraction of wide multiple systems, which
seems to decrease by a factor of about two on a timescale of
~10
5 yr. For the first time it is possible to
confront the result of a multiplicity survey of a nearly
complete population of embedded YSOs at an age of
~10
5 yr to numerical simulations of molecular
cloud collapse which, after a few free fall times, reach
this evolutionary stage. Somewhat contrary to model
predictions, we do not find evidence for a sub-clustering
of embedded sources at this stage on a scale of a few
100 AU that could be related to the formation of small-
N
protostellar clusters. Possible interpretations of this
discrepancy are discussed.
Key words: stars: formation -- stars: binaries: visual -- stars: pre-main sequence
SIMBAD Objects
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