Issue |
A&A
Volume 464, Number 2, March III 2007
|
|
---|---|---|
Page(s) | 581 - 599 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20054396 | |
Published online | 27 November 2006 |
A brown dwarf desert for intermediate mass stars in Scorpius OB2? *,**
1
Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: t.kouwenhoven@sheffield.ac.uk; [kouwenho;lexk]@science.uva.nl
2
Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: brown@strw.leidenuniv.nl
Received:
21
October
2005
Accepted:
21
November
2006
We present JHKS observations of 22 intermediate-mass stars in the
Scorpius-Centaurus OB association, obtained with the NAOS/CONICA system at the
ESO Very Large Telescope. This survey was performed to determine the status of (sub)stellar candidate companions of Sco OB2 member stars of spectral type A and
late-B. The distinction between companions and background stars
is made on the basis of a comparison to isochrones and additional statistical arguments. We are sensitive to companions with
an angular separation of (
AU) and the detection limit is
mag.
We detect 62 stellar components of which 18 turn out to be physical companions, 11 candidate companions, and 33 background stars. Three of the 18 confirmed companions were previously undocumented
as such. The companion masses are in the range
, corresponding to mass ratios
.
We include in our sample a subset of 9 targets with multi-color ADONIS observations from Kouwenhoven et al. (2005, A&A, 430, 137).
In the ADONIS survey secondaries with
mag were classified as companions; those with
mag as background stars. The multi-color analysis in this paper demonstrates that the simple
mag criterion correctly classifies the secondaries in ~80% of the cases. We reanalyse the total sample (i.e. NAOS/CONICA and ADONIS) and conclude that of the 176 secondaries, 25 are physical companions, 55 are candidate companions, and 96 are background stars. Although we are sensitive (and complete) to brown dwarf companions as faint as
mag in the semi-major axis range
AU, we detect only one, corresponding to a brown dwarf companion fraction of
(
).
However, the number of brown dwarfs is consistent with an extrapolation of the (stellar) companion mass distribution into the brown dwarf regime.
This indicates that the physical mechanism for the formation of brown dwarf companions around intermediate mass stars is similar to that of stellar companions, and that the embryo ejection mechanism does not need to be invoked in order to explain the small number of brown dwarf companions among intermediate mass stars in the Sco OB2 association.
Key words: binaries: visual / binaries: general / stars: formation / stars: low mass, brown dwarfs / open clusters and associations: individual: Sco OB2
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.