High mass star binary fraction
Hugues Sana
Nov 10 2007
H. Sana -- Fellow Days 2007
High mass star binary fraction
Holy Grail :
search for observational constraints on the
massive star formation
Nov 10 2007
H. Sana -- Fellow Days 2007
O-type stars
!"#$sol#%#!&
!#P)1#Q#B6#CR#%#%+--#%#:"#CR
!#S.D34).0Q#"T!6:#S0)/#%#&&#%#"T!6"#S0)/
!#0<),1#/3-+713D+#E2#-+*#!6U#9,I
!#-+*#34#4.DV+,
!#W342,9#-,+X.+4;9#30#<3K<
!#$200#,213)#30#/)*#E$!H$A@!7BI
' ()*+,-./#01+//2,#*3450
!!678#$sol#9,7!#%## &#%#!67:#$sol#9,7!#!#2--+;1#1<+#012,=0#+>)/.13)4
!#"?#@#A6667B666#CD#07!###E#"#F#"?#E!G#&H$Iβ ; β = 0.8−1.0)
' $234#0).,;+#)-#3)43J34K#,253213)40
' L1,)4K#34-/.+4;+#E,253213>+#M#C34+13;#+4+,K9N#;<+D3;2/#34O.1I
Nov 10 2007
H. Sana -- Fellow Days 2007
3
O-type stars
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"
"
!#S.D34).0Q#"T!6:#S0)/#%#&&#%#"T!6"#S0)/
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!#-+*#34#4.DV+,
Binary
frequency is high
What's the observational biases ?
!#W342,9#-,+X.+4;9#30#<3K<
Mass
ratio is low (M1/M2~1-3)
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' $234#0).,;+#)-#3)43J34K#,253213)40
' L1,)4K#34-/.+4;+#E,253213>+#M#C34+13;#+4+,K9N#;<+D3;2/#34O.1I
Nov 10 2007
H. Sana -- Fellow Days 2007
4
O-type stars are rare
#
4-15 Msol
#
13 A stars
2-4 Msol
#
19 F stars
1.2-2 Msol
22 G stars
0.8-1.2 Msol
141 K stars
0.5-0.8 Msol
295 M stars
0.1-0.5 Msol
Nov 10 2007
#
#
#
15-100: Msol
9 B stars
#
“Tonight, looking at the sky, I came
to the conclusion that they were
many more stars that what we
need.”
Mafalda (Quino)
1 O star
H. Sana -- Fellow Days 2007
5
O-type stars are rare
#
1 O star
15-100: Msol
9 B stars
4-15 Msol
#
13 A stars
2-4 Msol
#
19 F stars
1.2-2 Msol
22 G stars
0.8-1.2 Msol
141 K stars
0.5-0.8 Msol
295 M stars
0.1-0.5 Msol
#
Open clusters naturally provide homogeneous
unbiased sample of massive stars
“Tonight, looking at the sky, I came
to the conclusion that they were
many more stars that what we
need.”
Mafalda (Quino)
Nov 10 2007
#
#
#
H. Sana -- Fellow Days 2007
6
Nearby clusters rich in O stars
!"#$%"&'&()#*%++%,-&.//01&2'2&3451&0..
Nov 10 2007
H. Sana -- Fellow Days 2007
7
Nearby clusters rich in O stars
Loose
Dense
Suggestion : anticorrelation between cluster density and
binary fraction
!"#$%"&'&()#*%++%,-&.//01&2'2&3451&0..
Nov 10 2007
H. Sana -- Fellow Days 2007
8
Nearby clusters rich in O stars
Loose
Dense
Suggestion : anticorrelation between cluster density and
binary fraction
!"#$%"&'&()#*%++%,-&.//01&2'2&3451&0..
Nov 10 2007
H. Sana -- Fellow Days 2007
9
Observational sample
IC 2944
#
13 O stars
#
~ 100 spectra (+70 coming)
#
2 epochs (a 3rd coming)
NGC 6231
#
15 O stars + 1 WR
#
> 500 spectra
#
Large number of epochs
NGC 6611
HiRes high SNR:
#
#
Nov 10 2007
R > 30000
SNR > 150
H. Sana -- Fellow Days 2007
#
12 O stars
#
~ 40 spectra
#
2 epochs (3rd submitted)
10
Keplerian Doppler shifts
Nov 10 2007
H. Sana -- Fellow Days 2007
11
Multiple signatures & opposite RV shifts
Nov 10 2007
H. Sana -- Fellow Days 2007
12
Criteria for spectroscopic binaries
Keplerian Doppler shifts
or
Multiple spectral signature + opposite RV variations
Definite proof of binarity
Complete O star population ==>
Minimal binary fraction = Nbinary/Nstars (firm limit)
Nov 10 2007
H. Sana -- Fellow Days 2007
13
NGC 6231
Short period
Single stars ?
Long period
HD152234
HD152247
HD152233
HD152314
127d
~400d
~800d
~3100d
HD152076
HD152200
HD152249
HD326329
HD326331
CPD-41 7721
O9.7I+O8V
O9III+O9.7V
O6III(f)+O8-9V:
O8.5V+B1-3V/III
O9.5III
O9.7V
O9Ib((f))
O9.5V
O8III((f))
O9V
fmin = Nbinaries/Nstars= 10/16 = 0.63
Nov 10 2007
H. Sana -- Fellow Days 2007
14
6"7"&)8&"+&9.//:;1&(<=261&>?@*%88)-
Significance
In NGC6231:
fmin = 0.63 <= ftrue <= 1.0
(no error -->firm limit !!!)
Significance for a larger population :
fpopul > 0.37
@ α=0.01
(if following the same statistical distribution than
in NGC6231)
Nov 10 2007
H. Sana -- Fellow Days 2007
15
6"7"&)8&"+&9.//:;1&(<=261&>?@*%88)-
Towards a larger sample
No significant difference between the 3 clusters
In total : fmin=Nbinaries/Nstars=25/41=0.61
fpopul > 0.44
Nov 10 2007
@ α=0.01
H. Sana -- Fellow Days 2007
16
Binary frequency in clusters
0.63
0.61
0.58
Nov 10 2007
H. Sana -- Fellow Days 2007
17
Binary frequency in clusters
0.18 !!! (Debecker et al. 2005, A&A)
0.63
0.61
0.58
0.27
Nov 10 2007
H. Sana -- Fellow Days 2007
18
Binary frequency in clusters
Relation between cluster density and
0.18 !!!
binary fraction still need confirmation
0.63
(Can we really reject the
0.61
0.58 that
hypothesis
all Young Open Clusters have
0.27
a similar massive binary fraction
?)
Nov 10 2007
H. Sana -- Fellow Days 2007
19
Mass distribution of the companions
Random pairing
from Salpeter IMF
#
#
#
Nov 10 2007
H. Sana -- Fellow Days 2007
9 O+B stars
#
13 O+A stars
#
19 O+F stars
#
#
1 O+O star
22 O+G stars
141 O+K stars
295 O+M stars
20
Mass distribution of the companions
Random pairing
from Salpeter IMF
#
#
In NGC 6231 (16 objects)
10 SB2 binaries:
"
1 WR+O
"
5 O+O
"
4 O+B (B1-B4)
Nov 10 2007
#
H. Sana -- Fellow Days 2007
9 O+B stars
#
13 O+A stars
#
19 O+F stars
#
#
1 O+O star
22 O+G stars
141 O+K stars
295 O+M stars
21
Mass distribution of the companions
Random pairing
from Salpeter IMF
#
#
#
In NGC 6231 (16 objects)
#
10 SB2 binaries:
"
1 WR+O
"
5 O+O
"
4 O+B (B1-B4)
Nov 10 2007
#
#
#
H. Sana -- Fellow Days 2007
1 O+O star
9 O+B stars
13 O+A stars
195O+F
@
σ stars
22 O+G stars
141 O+K stars
295 O+M stars
22
Conclusions
#
fmin ~ 0.6 in 3 young open clusters
#
#
#
25 binaries/41objects --> fpopul > 0.44 @ 0.01 level
--> possibility to test whether all YOCs have the same binary
distribution or whether there is some relation between f and the
cluster properties
Massive star campanions are not randomly drawn
from a Salpeter IMF
#
--> strong bias towards O+OB systems (q~1-3)
Nov 10 2007
H. Sana -- Fellow Days 2007
23