Issue |
A&A
Volume 379, Number 1, November III 2001
|
|
---|---|---|
Page(s) | 147 - 161 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20011305 | |
Published online | 15 November 2001 |
Visual binaries among high-mass stars
An adaptive optics survey of OB stars in the NGC 6611 cluster
1
Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
2
Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA 90095-1562, USA
3
Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
4
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
Corresponding author: G. Duchêne, duchene@astro.ucla.edu
Received:
27
June
2001
Accepted:
19
September
2001
We have searched for visual binaries with projected
separations in the range 200-3000 AU (01-1
5) among a
sample of 96 stars in the massive young NGC 6611 cluster, 60 of
them being subsequently identified as high probability cluster
members of mainly OB spectral type. This is the first visual binary
survey among such a large and homogeneous sample of high-mass
stars. We find an uncorrected binary frequency of
%
over the surveyed separation range. Considering only binaries with
mass ratios
, we find that OB stars in NGC 6611
host more companions than solar-type field stars. We derive mass
ratios for the detected binaries from their near-infrared flux
ratios and conclude that about half of the detected binaries have
, which does not contradict the assumption that
companion masses are randomly drawn from the initial mass
function. There is no evidence in our sample that wide-binary
properties depend upon the mass of the primary star. The high
frequency of massive binaries in a cluster as rich as NGC 6611 and
the lack of a strong mass dependence of their properties are
difficult to reconcile with the scenario whereby massive stars form
as the result of mergers of smaller stars. The canonical
protostellar accretion scenario together with cloud fragmentation,
on the other hand, can naturally explain most of the observed
binary properties, although the very high stellar density in the
protocluster is likely to require significant modification to
that picture as well.
Key words: stars: binaries: visual / stars: formation / stars: early-type / Galaxy: open clusters and associations: individual: NGC 6611
© ESO, 2001
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