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Stalking the Elusive Brown Dwarf:
Wisdom from WISE in the Search for Roomtemperature Stars
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Three Questions
– What is a Brown Dwarf?
– What is WISE?
- What can WISE tell you about the Galactic population of
Brown Dwarfs?
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Brown Dwarf “Stars”
Postulated in 1963 by Shiv Kumar at....
Notes.html
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Brown Dwarf “Stars”
Postulated in 1963 by Shiv Kumar at....
the University of Virginia (well, just before he came
here)
Notes.html
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Brown Dwarf “Stars”
“Stars” that are insufficiently massive to heat their
interiors to the ignition point for hydrogen fusion.
• - critical temperature is ~10,000,000K
Notes.html
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Brown Dwarf “Stars”
The central temperature of any star is entirely determined
by mass and configuration/size.
Take a ball of hydrogen... gravity will squeeze it smaller
with time and make the center hotter until ignition
occurs to stabilize the configuration.
•
l
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Brown Dwarf “Stars”
That is.... unless something gets in the way – like the
electrons.
The Pauli Exclusion Principle keeps us all from collapsing
and thwarts hydrogen burning in balls of hydrogen that
are insufficiently massive.
Notes.html
Jupiter
(0.1% of the
mass of the
Sun)
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Brown Dwarf “Stars”
Compression starts things out hot, but low-mass objects
( < 8% of the mass of the sun) never can get hot
enough for fusion.
The resulting lump of hydrogen cools to invisibility over
time.
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Brown Dwarf “Stars”
Compression starts things out hot, but not hot enough for
fusion.
The resulting lump of hydrogen cools to invisibility over
time.
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Finding Brown Dwarfs
Not so easy because
- They are cool enough that they emit primarily
infrared radiation.
- They are faint. Even with infrared eyes you can only
readily detect the closest ones.
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Finding Brown Dwarfs
Not so easy because
- They are cool enough to emit primarily infrared
radiation.
- They are faint. Even with infrared eyes you can only
readily detect the closest ones.
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Finding Brown Dwarfs
The key... an ability to search large areas of sky for faint
infrared sources.
No infrared array detectors/cameras available until 1984.
First unquestionable brown dwarf discovered in 1995.
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Finding Brown Dwarfs
The Two Micron All Sky Survey mapped the entire sky at
near-infrared wavelengths between 1997 and 2001.
– resulted in the discovery of hundred of (“warm”) brown dwarfs
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The Wide-Field Infrared Survey Explorer


NASA Explorer program ($300M)
“WISE” mapped the entire sky at
infrared wavelengths
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

3, 5, 12, and 22 micrometers to be
specific.
Solid hydrogen cooled the
detectors and telescope to
temperatures as low as 8 degrees
above absolute zero.
WISE launched from Vandenberg
Air Force Base on a Delta-2
rocket on December 14, 2009.
−
The rocket placed the spacecraft in a
500 km high nearly-polar orbit
−
WISE continually orbits over the
sunrise/sunset line.
The WISE End-to-End Optical System
Primary Mirror
Baffles and vanes
minimize stray light
Scanner mounts to imager
optics module
Imager module
provides common
imaging optics for
all 4 channels
Entire assembly mounts at a
single cryostat interface ring
Aluminum
baffle tube
Spider and
secondary mirror
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Transporting to the launch pad
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WISE in the Fairing
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The Other US Spaceport(s)

Everybody knows about Kennedy Space Center in Florida.
−
Satellites are also launched into Earth orbit from Vandenberg, CA and
Wallops Island, VA.
−
Vandenberg is important because it enables safe launches to polar orbit.
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WISE Orbit
WISE orbits over the poles
(inclination 97 degrees)
pointing away from the
Earth.
The orbit lies over the
sunrise-sunset line and
precesses to stay there as
the Earth orbits the Sun.
- WISE always points 90degrees from the Sun and
away from Earth.
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Previous Survey in W1 & W2
WISE First
Light Image
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Zoom in
on DIRBE
Ecliptic
North
1.15 degree field
at (l,b) = (279,-5)
Moon to scale
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DIRBE 3.5
microns
IRAS 12 microns
WISE
3.4, 4.6, 12
microns
47’ FOV
2.75” pixels
6” FWHM
V482 Car
One Square Degree Covered to Full Survey Depth
(8+ exposures) Every 6 Minutes
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33 seconds in the life of WISE, 3 of >7000 frames/day
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•
Heart & Soul, IC 1848 & 1805, Maffei 2 & 1, 5.5x3.9 deg, N is UP
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• Menkhib & the California Nebula
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• IC 410
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• IC 410
• Asteroids
– 1719 Jens
– 1992 UZ5
• Satellites in
high orbit
Asteroids Observed by WISE
•
Four frames of data
taken on 2010 Jan. 8
during in-orbit
checkout.
•
Blue = 3.6um; green
= 4.6um; red =
12um
•
Circled asteroids are
(L to R in the first
frame, diameters in
km):
17818 MBA
D~12.4
153204 MBA
D~2.8
22006 MBA D~11.5
87355 MBA D~4.3
80590 MBA
Field of view = 34 x 25 arcmin (whole WISE FOV is 47 x 47
D~4.1
arcmin)
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Finding Brown Dwarfs with WISE
WISE's two short-wavelength bands (3.4 and 4.5um) are
fine tuned to isolate the unique spectral features of
brown dwarfs.
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Finding Brown Dwarfs with WISE
WISE's two short-wavelength bands (3.4 and 4.5um) are
fine tuned to isolate the unique spectral features of
brown dwarfs.
It Works!
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Spectroscopic Results
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The Quest for WISE Y's
Prior to WISE, the coolest brown dwarfs known had
temperatures around 500K.
Already the standard spectra sequence had been
extended
O, B, A, F, G, K, M, L, T....
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Finding Y Dwarfs with WISE
WISE's two short-wavelength bands (3.4 and 4.5um) are
fine tuned to isolate the unique spectral features of
brown dwarfs.
This should
be easy....
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Finding Y Dwarfs with WISE
WISE's two short-wavelength bands (3.4 and 4.5um) are
fine tuned to isolate the unique spectral features of
brown dwarfs.
This should
be easy....
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Finding Y Dwarfs with WISE
WISE's two short-wavelength bands (3.4 and 4.5um) are
fine tuned to isolate the unique spectral features of
brown dwarfs.
This should be easy....but it's not as easy as it looks...
– candidates can be identified readily
– identification and characterization requires spectra
– These things are FAINT
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Finding Y Dwarfs with WISE
WISE's two short-wavelength bands (3.4 and 4.5um) are
fine tuned to isolate the unique spectral features of
brown dwarfs.
This should be easy....but it's not as easy as it looks...
– candidates can be identified readily
– identification and characterization requires spectra
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A Two Step Process
1) Triage candidates with near-infrared photometry
(images)
Even Fan Mountain's Infrared Camera plays a role
First Spectroscopically Confirmed
WISE Brown Dwarfs
WISE 2
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•
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WISE 2 spectrum from LUCIFER on LBT.
As cool or cooler than any known BD
Mainzer et al 2010
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A Two Step Process
2) Throw everything at it, including the kitchen sink (in this
case the Hubble Space Telescope)....
– Near-infrared spectroscopy with the HST grism.
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Why is it Important?
As expected, brown dwarfs are numerous, possibly
outnumbering hydrogen-burning stars.
There are good odds that we have yet to find the nearest
“star” and it will be revealed by WISE
Results:
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W1-W2 vs.
Type
Oranges = known K, M, L, T dw
Classification
J and H zoom-ins showing new T9 anchor
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Photometric Confirmation and Classification with
Fancam
(and ultimately proper motions and parallaxes)
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MBA Diameters and Albedos
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Inhabitants of WISE Color Space
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• LBN 1037, 3.6x1.4 degrees
(about ½ hour in the life of WISE)
Selection Method
Models from
Burrows et al. (2003)
Wright et al. (2010)
WISE’s filters were designed for sensitivity to
the coldest brown dwarfs.
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