The
Brown
Dwarf
Multiplicity
Fraction:
Are
Most
Brown
Dwarfs
in
(Tight)
Multiples?
Adam
J.
Burgasser
UC
San
Diego/MIT
20%
?
WHAT
IS
THE
BROWN
50% DWARF
MULTIPLICITY
?
FRACTION
IN
THE
FIELD?
10%?
©
2009
Adam
J
Burgasser
Lada
(2006):
5‐15%
Bate
et
al.
(2009):
5‐20%
Thies
&
Kroupa
(2007):
5‐15%
©
2009
Adam
J
Burgasser
“BD
binary
fractions
are
low”
But
are
they?
Lada
(2006):
5‐15%
Bate
et
al.
(2009):
5‐20%
Thies
&
Kroupa
(2007):
5‐15%
©
2009
Adam
J
Burgasser
Pinfield
et
al.
(2003):
40‐61%!
Maxted
&
Jeffries
(2005):
32‐45%!
If
67%
L/T
transition
objects
are
binary
(Liu
et
al.
2006)
then
…
Burgasser
(2007):
24‐53%!
©
2009
Adam
J
Burgasser
http://www.vlmbinaries.org
©
2009
Adam
J
Burgasser
Number of Sources
30
~4
AU
VLM Binaries Archive
93 sources
25
20
15
10
5
0
10-2
100
102
104
Projected Separation (AU)
http://www.vlmbinaries.org
©
2009
Adam
J
Burgasser
Number of Sources
30
50
mas
VLM Binaries Archive
90 sources
25
20
15
10
How
many
sources
live
here?
5
0
10-2
100
102
104
Angular Separation (marcs)
106
http://www.vlmbinaries.org
©
2009
Adam
J
Burgasser
“Easy”
Ways
to
Find
Tight
BD
Binaries
•  Radial
velocity
variables
(e.g.,
Joergens
2006,2008;
Basri
&
Reiners
2006;
Blake
et
al.
2008)
Pros:
samples
tight
physical
separations
(<1‐5
AU);
direct
mass
measurement
Cons:
expensive,
impossible
for
faint
sources,
difficult
to
characterize
components
•  Overluminosities
in
CMD
(e.g.,
Pinfield
et
al.
2003;
Chapelle
et
al.
2005;
Burgasser
et
al.
2008)
Pros:
no
limit
on
separation,
cheap(ish)
Cons:
contamination
issues,
requires
cospatial
sample
or
accurate
distance
measurements
(not
cheap),
difficult
to
characterize
components
©
2009
Adam
J
Burgasser
Also
eclipsing,
microlensing,
etc.
Spectral
Binaries
Combined
light
spectra
of
distinct
but
comparably
bright
components
Pros:
independent
of
angular
&
projected
separation,
can
be
done
with
low‐resolution
data
(cheap),
can
characterize
components
Cons:
rare,
no
separation
info,
complex
selection
effects
Silvestri
et
al.
(2006)
WD‐dM
unresolved
pair
©
2009
Adam
J
Burgasser
Exploiting
the
L/T
Transition*
“J‐band”
bump
Deep
minimum
in
LF
An
enhanced
binary
fraction
of
equal‐
brightness
components
at
the
L/T
transition
*Spectral
types
L7‐T5
©
2009
Adam
J
Burgasser
2M
0518‐2828
Archetype
L/T
Spectral
Binary
1.2
0518-2828
Normalized F!
1.0
0.8
0.6
0.4
0.2
0.0
1.0
1.5
Wavelength (!m)
2.0
Cruz
et
al.
(2004);
Burgasser
et
al.
(2006)
©
2009
Adam
J
Burgasser
2M
0518‐2828
Archetype
L/T
Spectral
Binary
1.2
0518-2828
0825+2115 L7.5 (L7.0)
2331-4718 T5.0 (T5.0)
"2 = 58.9
Normalized F!
1.0
0.8
0.6
0.4
Resolved
(barely)
with
HST/NICMOS
(50
mas
≈
1.8
AU)
0.2
0.0
1.0
1.5
Wavelength (µm)
2.0
Cruz
et
al.
(2004);
Burgasser
et
al.
(2006)
©
2009
Adam
J
Burgasser
2M
0320‐0446
An
M/T
Spectral/Spectroscopic
Binary
Burgasser
et
al.
(2008);
Blake
et
al.
(2008)
©
2009
Adam
J
Burgasser
2M
0320‐0446
An
M/T
Spectral/Spectroscopic
Binary
ΔK
=
4.3
mag
Burgasser
et
al.
(2008);
Blake
et
al.
(2008)
Spectroscopic
binary
with
0.67
yr
period
(ΔV
=
±7
km/s;
M1
≈
0.08
M,
M2
≈
0.05
M
©
2009
Adam
J
Burgasser
Search
for
Unresolved
L/T
Binaries
•  Full
sample
of
253
SpeX
prism
spectra
for
233
L3‐T8
dwarfs
from
SpeX
Prism
Spectral
Libraries*
•  Index
selection
of
binary
candidates
•  Template
library
of
170
spectra
(reject
low
g,
subdwarfs,
low
S/N,
known
&
candidate
binaries)
•  Construct
13581
unique
binary
combinations
•  Compare
single
and
binary
templates
to
candidates
and
assess
statistical
significance
of
“better
fit”
©
2009
Adam
J
Burgasser
*
http://www.browndwarfs.org/spexprism
Index
Selection
1.2
2252-1730
H2O-J/H2O-H
1.0
0423-0414
0423-0414
1404-3159
1021-0304
0.8
1534+1615
0518-2828
0.6
0.4
0.2
L0
L2
L4
L6
L8
T0
T2
T4
T6
T8
Derived NIR Spectral Type
=>
21
candidates
identified
(12
“strong”
+
8
“weak”)
©
2009
Adam
J
Burgasser
1.2
0.2
0.2
0.0
1.5
Wavelength (µm)
2.0
2.0
0.6
0.4
0.2
0.8
0.6
0.4
0.0
1.5
Wavelength (µm)
2.0
1.5
Wavelength (µm)
Normalized F!
0.8
1.0
0.6
0.4
0.2
0.8
0.6
0.4
0.0
1.5
Wavelength (µm)
2.0
1.2
1.5
Wavelength (µm)
Normalized F!
0.8
1.0
0.6
0.4
0.2
0.8
0.6
0.4
0.2
0.0
1.5
Wavelength (µm)
2.0
0.6
0.4
1.5
Wavelength (µm)
2.0
0119+2403
0858+3256 T1.0 (T0.0)
2254+3123 T4.0 (T4.0)
"2 = 15.7
1.0
0.8
0.6
0.4
0.0
1.5
Wavelength (µm)
2.0
1.0
1.5
Wavelength (µm)
2.0
1.2
1207+0244
1036-3441 L6.0 (L6.5)
1209-1004 T3.0 (T3.0)
"2 = 6.14
1.0
0.8
0.6
0.4
2052-1609
1155+0559 L7.5 (L7.0)
1122-3512 T2.0 (T2.0)
"2 = 2.59
1.0
0.8
0.6
0.4
0.2
0.0
1.0
2.0
0.2
0.2
0.0
1.0
1.5
Wavelength (µm)
1.2
1.2
0949-1545
1632+4150 T1.0 (T1.0)
1122-3512 T2.0 (T2.0)
"2 = 13.7
Normalized F!
1.0
1.0
2139+0220
0830+4828 L9.0 (L9.5)
1214+6316 T3.5 (T4.0)
"2 = 1.83
1.0
1.2
0909+6525
1750+4222 T2.0 (T1.5)
1048+0919 T2.5 (T2.5)
"2 = 2.53
0.4
2.0
0.8
2.0
0.6
0.0
1.5
Wavelength (µm)
0.0
1.0
0.8
0.2
0.2
0.0
1.0
0.4
1.0
0.2
2.0
1439+3042
0151+1244 T1.0 (T0.0)
2356-1553 T5.5 (T5.5)
"2 = 4.85
1.0
1.2
1711+2232
0624-4521 L5.0 (L5.0)
1828-4849 T5.5 (T5.5)
"2 = 1.49
Normalized F!
1.0
0.6
1.0
1.2
1516+0259
0318-3421 L7.0 (L6.5)
1048+0919 T2.5 (T2.5)
"2 = 1.97
0.8
2.0
1.5
Wavelength (µm)
1.2
0.0
1.0
1.2
1.0
0.2
0.0
1.0
0.4
2.0
1435+1129
1043+1213 L7.0 (L8.0)
1615+1340 T6.0 (T6.0)
"2 = 19.9
1.0
0.2
0.6
0.0
1.5
Wavelength (µm)
1.2
Normalized F!
0.8
0.8
0.2
1.0
1415+5724
1523+3014 L8.0 (L7.5)
0741+2351 T5.0 (T5.5)
"2 = 1.73
1.0
Normalized F!
Normalized F!
1.0
Normalized F!
1.5
Wavelength (µm)
1.2
1324+6358
1043+2225 L8.0 (L9.0)
1214+6316 T3.5 (T4.0)
"2 = 6.17
0.4
0.0
1.0
1.2
0.6
0.2
0.0
1.0
Normalized F!
0.4
Normalized F!
0.4
0.6
0.8
1106+2754
1520+3546 T0.0 (L7.5)
0000+2554 T4.5 (T4.5)
"2 = 5.18
1.0
Normalized F!
0.6
0.8
1.2
1039+3256
1043+1213 L7.0 (L8.0)
2254+3123 T4.0 (T4.0)
"2 = 2.56
1.0
Normalized F!
0.8
1.0
Normalized F!
Normalized F!
1.0
1.2
0351+4810
0103+1935 L6.0 (L6.0)
0602+4043 T4.5 (T4.5)
"2 = 6.64
Normalized F!
0247-1631
1520+3546 T0.0 (L7.5)
0050-3322 T7.0 (T6.5)
"2 = 1.99
Normalized F!
1.2
©
2009
Adam
J
Burgasser
0.0
1.0
1.5
Wavelength (µm)
2.0
1.0
1.5
Wavelength (µm)
2.0
1.2
0247-1631
1520+3546 T0.0 (L7.5)
0050-3322 T7.0 (T6.5)
"2 = 1.99
0.6
0.2
0.0
0.0
0.8
0.6
0.4
0.2
0.0
0.8
2.0
1.0
0.6
1.5
Wavelength (µm)
0.4
1.0
0.8
0.6
2.0
1.5
Wavelength (µm)
2.0
0.8
0.6
1.5
Wavelength (µm)
2.0
1.0
1.2
1711+2232
0624-4521 L5.0 (L5.0)
1828-4849 T5.5 (T5.5)
"2 = 1.49
1.0
0.4
0.0
1.0
1.2
1.5
Wavelength (µm)
0.6
0.4
1.0
0.2
1.0
2.0
0.8
0.6
0.4
0.2
0.0
1.5
Wavelength (µm)
1.5
Wavelength (µm)
2.0
1.5
Wavelength (µm)
0.6
0.4
0.2
0.8
0.6
0.4
0.2
0.0
1.5
Wavelength (µm)
2.0
1.0
0.8
0.6
0.4
1.5
Wavelength (µm)
2.0
2.0
2052-1609
1155+0559 L7.5 (L7.0)
1122-3512 T2.0 (T2.0)
"2 = 2.59
1.0
0.8
0.6
0.4
0.2
0.0
1.0
1.5
Wavelength (µm)
1.2
1207+0244
1036-3441 L6.0 (L6.5)
1209-1004 T3.0 (T3.0)
"2 = 6.14
0.2
0.0
1.0
0.4
1.0
12
are
unobserved
at
high
resolution
1.0
0.6
2.0
1.2
0949-1545
1632+4150 T1.0 (T1.0)
1122-3512 T2.0 (T2.0)
"2 = 13.7
0.8
0.0
1.0
1.2
0909+6525
1750+4222 T2.0 (T1.5)
1048+0919 T2.5 (T2.5)
"2 = 2.53
0119+2403
0858+3256 T1.0 (T0.0)
2254+3123 T4.0 (T4.0)
"2 = 15.7
0.2
0.0
1.0
2.0
1.2
2139+0220
0830+4828 L9.0 (L9.5)
1214+6316 T3.5 (T4.0)
"2 = 1.83
2
have
been
subsequently
resolved
with
AO
(Gelino
et
al.
in
prep.)
0.8
1439+3042
0151+1244 T1.0 (T0.0)
2356-1553 T5.5 (T5.5)
"2 = 4.85
0.2
0.0
1.0
1516+0259
0318-3421 L7.0 (L6.5)
1048+0919 T2.5 (T2.5)
"2 = 1.97
0.4
0.2
0.0
1.5
Wavelength (µm)
2.0
1.2
1435+1129
1043+1213 L7.0 (L8.0)
1615+1340 T6.0 (T6.0)
"2 = 19.9
1.0
0.2
Normalized F!
1.0
1.5
Wavelength (µm)
1.2
0.8
0.4
3
are
unresolved
with
HST/AO
(Looper
et
al.
2008;
Gelino
et
al.
in
prep)
1.0
1.2
0.6
0.0
1.0
1415+5724
1523+3014 L8.0 (L7.5)
0741+2351 T5.0 (T5.5)
"2 = 1.73
1.0
Normalized F!
Normalized F!
1.0
2.0
1.2
1.0
1.2
1.5
Wavelength (µm)
Normalized F!
0.4
0.8
0.2
0.0
1.0
1324+6358
1043+2225 L8.0 (L9.0)
1214+6316 T3.5 (T4.0)
"2 = 6.17
0.6
0.2
Normalized F!
2.0
0.4
Normalized F!
0.8
1.5
Wavelength (µm)
Normalized F!
Normalized F!
1.0
0.6
Normalized F!
1.0
1.2
0.8
0.2
Normalized F!
0.0
1106+2754
1520+3546 T0.0 (L7.5)
0000+2554 T4.5 (T4.5)
"2 = 5.18
1.0
We
identified
17/21
sources
as
probable
binaries
(index
selection,
better
fit
to
binary
templates)
0.4
Normalized F!
0.2
0.6
Normalized F!
0.4
0.8
1.2
1039+3256
1043+1213 L7.0 (L8.0)
2254+3123 T4.0 (T4.0)
"2 = 2.56
1.0
Normalized F!
0.8
1.0
Normalized F!
Normalized F!
1.0
1.2
0351+4810
0103+1935 L6.0 (L6.0)
0602+4043 T4.5 (T4.5)
"2 = 6.64
Normalized F!
1.2
©
2009
Adam
J
Burgasser
0.0
1.0
1.5
Wavelength (µm)
2.0
1.0
1.5
Wavelength (µm)
2.0
What
about
the
binary
fraction?
0/12 (21)
1/9 (13)
6/9 (14)
8/17 (20)
3/7 (13)
1/10 (20)
eb = 15%
80
Fraction of Binaries
6/10 (15)
60
40
20
0
L8
L9
T0
T1
T2
T3
Spectral Type
T4
T5
©
2009
Adam
J
Burgasser
What
about
the
binary
fraction?
0/12 (21)
1/9 (13)
6/9 (14)
6/10 (15)
8/17 (20)
1/10 (20)
eb = 15%
80
Fraction of Binaries
3/7 (13)
60
53±7%
40
eb
≥
15+3‐1
%
20
0
L8
L9
T0
T1
T2
T3
Spectral Type
T4
T5
©
2009
Adam
J
Burgasser
Conclusions
•  Spectral
binaries
comprised
of
L
dwarf/T
dwarf
pairs
can
measure
the
intrinsic
BD
binary
fraction
–  Indep.
of
physical
separation
(tight
pairs;
e.g.
2m0320)
–  Indep.
of
angular
separation
(distant
pairs,
large
samples)
–  Can
be
done
cheap
and
fast
with
low‐res
spectral
data
•  We
uncovered
17
(+3)
probably
binaries;
a
few
confirmed,
most
awaiting
follow‐up
•  The
BD
binary
fraction
is
≥15%
independent
of
separation
distribution
©
2009
Adam
J
Burgasser
The
Brown
Dwarf
Multiplicity
Fraction:
Are
Most
Brown
Dwarfs
in
(Tight)
Multiples?
Adam
J.
Burgasser
UC
San
Diego/MIT