Sniffing Out Brown
Dwarfs with
Methane Imaging
Temperature
O
B
A
F
G
K
M
Oh
Be
A
Fine
Guy / Girl
Kiss
Me
L
T
Lustily?
Tonight?
6000K
3000K
1500K
1000K
Stars & Brown Dwarfs
Brown Dwarfs
Chris Tinney, Simon Ellis (AAO), Adam Burgasser, Michael McElwain (UCLA), Davy Kirkpatrick (IPAC)
A Good Brown Dwarf
is Hard to Find
Rare
Large area
critical
Lots of “crap”
L-dwarfs
Pick red things
T-dwarfs
Red in optical-IR
Everything in IR!
A Good Brown Dwarf
is Hard to Find
2MASS Wide Field T-dwarf Search - Part the First
Colour selection.
|b|>15°, |δ| < 88° exclude LMC, SMC, 47Tuc, Orion, etc.
=> 30400 sq.deg. (74% of sky)
264,000 candidates (of 1.3x106 2MASS objects)
No optical counterparts in USNO A2.0.
Visually examine all in DSS => 1500 cands.
2MASS Wide Field T-dwarf - Part the Second
Infrared imaging … is there really an object there?
Optical imaging … is there really no counterpart?
Infrared low-res spectroscopy … is it a T-dwarf?
Expect around 35-50 T-dwarfs in 2MASS
A Better Way
CH4s
CH4l
Zero-point defined by A,F,G stars
Differential Photometry
IRIS2 7.7’x7.7’
Methane 2-colour
Diff = 0.036±0.001 +
(1.008±0.004) Abs
Science Online !
IRIS2 Spectra
New T-dwarfs
Known T-dwarfs
Methane Imaging
• It works. Its easy. Its fast.
• Other applications
– Unbiased T-dwarf search
• ie. direct CH4 imaging of ‘blank’ sky
• VISTA?
– “Free floating planets” in clusters
– “Things around other things”
– Weather?
– “Winnowing” next-gen surveys like UKIDSS
“Free floating planets”
•
Can we probe the 5-20Mjup range?
“Weather”
Gaps in Jupiter’s
CH4 cloud layers
allow the lower
photosphere to
shine out at
4.8um
A great leap forward- UKIDSS
• Major new infrared survey being done at UKIRT with
a new camera - WFCAM
• 4000 sq.deg to H=18.8, J=20.0, Y=20.5
• Survey volume 250 times greater than 2MASS. Can
see 800K T-dwarfs out to 20pc instead of 5pc.
• Beautifully suited to L,T,Y dwarfs.
• But there are still considerable challenges
Winnowing UKIDSS
Recall T dwarfs in 2MASS 35 from 1.3 billion sources!
O-K
M
O-K
“Y” m
L
M
odels
T
L
T