Ray Butler Centre for Astronomy Na3onal University of Ireland, Galway
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Ray
Butler
Centre
for
Astronomy
Na3onal
University
of
Ireland,
Galway
Leon
K.
Harding
(PhD
2012,
NUIG)
Gregg
Hallinan
(PhD
2008,
NUIG)
Aaron
Golden
(CfA,
NUIG)
Brendan
Sheehan
(PhD
2008,
NUIG)
Talk
Layout
• The
main
sequence
–
M-‐dwarfs
-‐>
ultracool
dwarfs
• Radio
emission
• GUFI
instrument
-‐>
opAcal
emission
• Flare
Stars
• ELTs
Project
MoAvaAon
• Low
mass
stars
&
brown
dwarfs*
(~2500
K)
discovered
as
a
transient
radio
source
(Berger
et
al.
2001)
• Harding,
PhD
thesis:
• Later:
periodic
bursts
of
radio
emission
–
similar
to
magneAzed
giant
planets
in
our
solar
system
(Hallinan
et
al.
2007)
[Hallinan,
PhD
2008,
NUIG)
• Do
these
elusive
radio-‐detected
objects
also
exhibit
opHcal
variability?
• What
are
the
characterisHcs
of
these
emissions?
How
does
magneHc
acHvity
behave
in
the
‘ultracool
dwarf’
regime?
• Is
there
some
causal
connecHon
between
the
opHcal
and
radio
variabiliHes?
Behave
like
planets??
What are Ultracool Dwarfs? Main sequence, spectral type > M7
Change in Fully convective
magnetic field (~M3, 0.3 – 0.4 Msol)
diagnostics
Cool & neutral
Atmospheres
Adapted from Reiners (2007)
Periodicity
in
the
Radio
Emission
• Berger et al. ApJ 627, 960 (2005)
-> L3.5 dwarf 2MASS J0036+18
-> period of ~3 hours
-> suggested incoherent gyrosynchrotron
radiation, low field strength
Credit:
Stephen
Bourke,
PhD
2008,
NUIG
• Hallinan et al. ApJ 653, 690-699 (2006)
-> M9 TVLM 513-46546
-> period of ~2 hours, 100% circularly
polarized pulses
-> suggested something else ...
Maybe
Brown
Dwarfs
Behave
like
Planets?
Planetary coherent radio
emission produced by the
electron cyclotron maser
instability
Responsible for the (pulsed)
radio emission from brown
dwarfs?
Would require large-scale,
stable and strong (kG)
magnetic field configurations
GUFI
high-‐speed
photometer
–
Galway
Ultra
Fast
Imager
On
the
1.8m
VATT,
MGIO
Arizona
Principal
InvesAgator:
Butler
V1
Instrument
ScienAst:
Sheehan
V2
Instrument
ScienAst:
Harding
•
512
x
512
pixels
(naAve)
•
>
90%
QE
•
34
fps
(full
frame)
–
526
fps
(windowed):
1
–
3
–
5
–
10
MHz
•
Readout
rate
~2
ms
Possible
Models
in
OpAcal?
•
-‐
MagneAc
spots
&
chromospheric
emission?
•
-‐
Dust
(very
sensiAve
to
dwarf
temperature)?
•
-‐
Other:
Collisional
excitaAon
of
atomic
and
molecular
species?
GUFI
Campaign
(January
2009
–
January
2012)
Brown
Dwarfs
• ObservaAons
of
radio
detected
dwarfs
visible
from
VATT
site
• Obtained
>250
hours
of
mulAcolour
photometric
data
Objects
1. LP
349-‐25AB
(M8V)
2. LSR
J1835+3259
(M8.5)
3. TVLM
513-‐46546
(M9)
4. BRI
0021-‐0214
(M9.5)
5. 2MASS
J0746+2000AB
(L0+L1.5)
6. 2MASS
J0036+18
(L3.5)
Harding et al. (2013), ApJ, 779, 101
Stability
in
Phase
and
Amplitude
of
the
M9
Dwarf
TVLM
513-‐46546
•
Stable
in
phase,
not
amplitude
•
~5
year
baseline
•
Suggests
a
stable
spaAal
feature
Causal
connecHon
to
the
radio
emission?
Auroral
Emission
Hβ
from
TVLM
513-‐46546
Hα
NA
D
TiO
Hallinan
et
al.
in
prep
GUFI
Results
Harding
et
al.
(2013),
ApJ,
779,
101
• Discovered
opAcal
variability
from
all
radio
detected
dwarfs
– OpAcal
variability
ubiquitous
for
radio
acAve
dwarfs?
– Case
for
magneAc
acAvity
associated
with
opAcal
variability
– Cannot
rule
out
dust!
– Phase
and
amplitude
stability
-‐>
unchanging
spaAal
and
thermal
feature
• All
radio
pulsing
dwarfs
also
periodically
variable
in
opAcal
(3
newly
discovered;
2
confirmed
&
constrained)
From
this
work
…
Discovery
of
binary
dwarf
rotaAon
periods
have
allowed
for
another
invesAgaAon
…
Orbital
Coplanarity
of
VLM
Binary
Stars
• Hale
(1994)
demonstrated
coplanarity
between
equatorial
and
orbital
planes
of
solar-‐type
binaries
≤40
AU
separaAon
• Alignments
in
substellar
regime
poorly
constrained
• If
coplanarity
discovered
in
substellar
regime,
suggests
that
solar-‐type
model
of
binary
formaAon
applies
Confirmed
Discovery
of
Orbital
Coplanarity!
(Harding
et
al.
2013,
A&A,
554,
113)
• 2MASS
J0746+20AB
spin
axes
perpendicularly
aligned
with
orbital
plane
to
within
10°
• First
direct
measurement
of
this
formaAon
property
in
very
low
mass
regime
• LP
349-‐25B
consistent
with
coplanar
alignment
based
on
model
radii
and
v
sin
i
Harding
et
al.
(2013)
refutes
claimed
radius
of
Berger
et
al.
(2009)
and
age
range
of
Buoy
(2004)
Berger:
A:
0.78
R
J
Harding:
A:
0.99
R
J
B:
0.96
R
J
Flare
Star
GUFI
Campaign
(February
2011
–
April
2011)
Flare
Stars
• Resolve
small
structures
in
flaring
• Obtained
>110
hours
of
mulAcolour
photometric
data
Objects
(early
to
mid-‐M
dwarfs)
1. UV
CeA
6.
GL
51
2. GJ
2069b
7.
VB
10
3. GL
1111
8.
AD
Leo
4. CN
Leo
9.
YZ
CMi
5. LHS
3376
Loop
OscillaAons
in
Decay?
YZ
CMi,
B-‐
band.
~1.2
minutes
rise,
~8
minutes
decay,
10-‐15
seconds
P_osc
Harding
et
al.
2014,
in
prep
Extremely
Large
Telescopes
&
parameter
space
Telescope
Aperture
Area
First
Light
Loca3on
E-‐ELT
39.9-‐m
978
m^2
2022
Chile
TMT
30
655
m^2
2022
Hawaii
GMT
24.5
368
m^2
2020
Chile
• Magnitude-‐limited
sample
-‐
despite
very
local
volume
of
space
-‐
ELTs
would
vastly
increase
known
populaAon
size.
• Millimag
modulaAon/variaAon
of
faint
objects
-‐
ELTs
would
bring
a
big
leap
in
lightcurve
S/N
-‐
Improved
period,
amplitude,
stability
measures
-‐
Constrain
dust/spots/aurora
emission
mechanisms
-‐
InvesAgate
behaviour
on
shorter
Amescales
-‐
Exoplanet
aurorae?
• Long
ELT
campaigns
unlikely…
Thank
you!
QuesAons?
Butler:
ray.butler@nuigalway.ie;
Harding:
lkh@astro.caltech.edu
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