J/A+A/464/581 Sco OB2 intermediate-mass stars (Kouwenhoven+, 2007)
A brown dwarf desert for intermediate mass stars in Scorpius OB2?
Kouwenhoven M.B.N., Brown A.G.A., Kaper L.
<Astron. Astrophys. 464, 581 (2007)>
=2007A&A...464..581K 2007A&A...464..581K
ADC_Keywords: Clusters, open ; Stars, double and multiple ; Photometry, infrared
Keywords: binaries: visual - binaries: general - stars: formation -
stars: low-mass, brown dwarfs -
open clusters and associations: individual: Sco OB2
Abstract:
We present JHK observations of 22 intermediate-mass stars in Sco OB2,
obtained with NACO. 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 include in our sample a
subset of 9 targets with multi-color ADONIS observations from
Kouwenhoven et al. (2005, Cat. J/A+A/430/137). We reanalyse the
total sample (i.e. NACO 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 K=14mag in the semi-major axis
range 130-520AU, we detect only one, corresponding to a brown dwarf
companion fraction of 0.5% (M>30MJupiter). 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 Sco OB2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 49 31 Targets
table4.dat 78 25 Confirmed companion stars
tablea1.dat 78 103 Results of NACO observations
tablea2.dat 41 72 Background star criteria
tablea3.dat 88 81 Combined ADONIS/NACO results
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See also:
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
J/A+A/430/137 : Close visual companions in Scorpius OB2 (Kouwenhoven+, 2005)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- HIP Hipparcos number
7- 12 I6 --- HD HD number
14- 18 F5.2 mas plx Trigonometric parallax
20- 23 F4.2 mas e_plx Parallax error
25- 29 F5.2 mag Ksmag Ks magnitude
31- 38 A8 --- SpType MK spectral type
40- 42 A3 --- Group Subgroup (1)
44- 49 A6 --- Inst Instrument (ADONIS or NACO)
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Note (1): Subgroups as follows:
LCC = Lower Centaurus Crux
UCL = Upper Centaurus Lupus
US = Upper Scorpius
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Byte-by-byte Description of file: table4.dat tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- HIP Hipparcos number
7- 8 I2 --- m_HIP [1/12]? Secondary designation
10- 14 F5.2 mag Jmag ? J magnitude
16- 20 F5.2 mag Hmag ? H magnitude
22- 26 F5.2 mag Ksmag ? Ks magnitude
28- 32 F5.2 arcsec rho ? Angular separation
34- 39 F6.2 deg PA ? Position angle (North to East)
41- 45 F5.2 mag JMAG ? Absolute J magnitude
47- 51 F5.2 mag HMAG ? Absolute H magnitude
53- 57 F5.2 mag KsMAG ? Absolute Ks magnitude
59- 63 F5.2 solMass Mass ? Companion mass
65- 66 A2 --- Status Secondary status (G1)
68- 73 A6 --- Inst Instrument (ADONIS or NACO)
75- 78 A4 --- Remarks [JHKjhkm! ] See note (2)
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Note (2): Remarks flag as follows:
J = Secondary flux in filter J obtained from image without NDF using
the PSF of the corresponding image with NDF
H = Secondary flux in filter H obtained from image without NDF using
the PSF of the corresponding image with NDF
K = Secondary flux in filter Ks obtained from image without NDF using
the PSF of the corresponding image with NDF
j = The J magnitude and absolute J magnitude are lower limits
h = The H magnitude and absolute H magnitude are lower limits
k = The Ks magnitude and absolute Ks magnitude are lower limits
m = Uncertain mass estimate
! = Status of companion determined using one filter only
m = Uncertain mass estimate
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
-------------------------------------------------------------------------------
1- 5 I5 --- HIP Hipparcos number
7- 8 I2 --- m_HIP [1/12] Secondary designation
10- 11 A2 --- Status Secondary status (G1)
12- 17 F6.2 --- X(J-K,MK) ? Comparison with isochrone in (J-K,M_K)
diagram (1)
19- 24 F6.2 --- X(H-K,MK) ? Comparison with isochrone in (H-K,M_K)
diagram (1)
26- 30 F5.2 --- X(J-H,MJ) ? Comparison with isochrone in (J-H,M_J)
diagram (1)
32- 37 A6 --- Inst Instrument (ADONIS or NACO)
39- 41 A3 --- Remarks Lower limit flag (2)
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Note (1): Compatibility of the location of the object in the color-magnitude
diagrams with the isochrones in terms of chi2. Confirmed companions
have chi2<2.30 and (confirmed) background stars have chi2>11.8.
The other secondaries have 2.30<chi2<11.8 and are labeled "candidate
companion". A substantial fraction of these candidate companions may
in fact be background stars. Several faint (Ks>14mag) secondaries are
only detected in one filter (thus have no chi2), and are all assumed
to be background stars.
Note (2): Lower limit flag as follows:
1 = The value for X(J-K,MK) is a lower limit
2 = The value for X(H-K,MK) is a lower limit
3 = The value for X(J-H,MJ) is a lower limit
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- HIP Hipparcos number
7- 11 F5.2 mag Jmag ? J magnitude
13- 17 F5.2 mag Hmag ? H magnitude
19- 23 F5.2 mag Ksmag ? Ks magnitude
25- 29 F5.2 arcsec rho Angular separation
31- 36 F6.2 deg PA Position angle (North to East)
38- 49 A12 --- Status Companion status
51- 88 A38 --- Dates Observing dates
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Global notes:
Note (G1): Secondary status as follows:
p = primary star
c = companion star
nc = new companion star
? = candidate companion star
b = background star
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Acknowledgements:
M.B.N. Kouwenhoven, t.kouwenhoven(at)sheffield.ac.uk
(End) M.B.N. Kouwenhoven [Amsterdam Univ.], Patricia Vannier [CDS] 06-Mar-2007