Transcript direct detection

Exoplanets:
direct detection
ASTR 1420
Lecture 17
Sections 11.2
Imaging planet is hard!
Direct imaging is very hard, because…
tremendous brightness contrast ratio between stars and planets
(e.g.) Sun outshines Earth about 10 billion times
and Earth at 10pc (~32 Ly) would be separated
from the Sun by only ~0.1 arcsec.
1 arc second = angular extent of a penny seen
3.9 km (2.45 miles) away
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Direct Imaging of Exo-Planets (Jovian Planets)
• Reflected light detection of
Jovian planets requires 10-9
contrast ratio at  0.5

• Current state-of-the-art
achieves 10-4~-5 at 1.0
How can we do then?
Focus on nearby young stars
• “young” = planets are still ‘hot’
thus, much brighter than older planets!
• “nearby” = large separation between stars and planets!
normal stars (old & distant)
young distant stars
young & nearby stars!!!
4
Coronagraph
Blocking the bright region to see nearby faint stuffs…
Angular Resolution of Telescopes
Larger telescopes will produce sharper images…
Effect of Earth Atmosphere
• Light = wave
• Perfect wave form got deformed due to turbulence…
breeze
turbulence in atmosphere
Eliminate the effect of Atmosphere (Adaptive Optics)
Power of Adaptive Optics
Need for a confirmation!
• Actual Example from Keck AO
Need for a confirmation!
• Actual Example from Keck AO
Some early discoveries…
2M1207b
• European Very Large Telescope
o 2M1207b  central obj is a brown dwarf
o AB Pic B  companion is a BD
o GSC 8047-0232 B  companion is a BD
GSC 8047-0232 B
AB Pic B
Recent Discoveries
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In 2008, by Canadians, about 350 lightyears away in a star forming region…
In 2010, common proper motion was confirmed.
Wide separation (about 300 AU)  probably not formed as a planet.
In 2012, the companion is estimated to be a brown dwarf.
Fomalhaut
direction of Fomalhaut movement
HR 8799
Direct Imaging of Planetary System!
C. Marois,
B. Macintosh,
T. Barman,
B. Zuckerman,
Inseok Song,
J. Patience,
D. Lafreniere,
R. Doyon
Science (2008)
• 4th planet was discovered in 2010
HR 8799
• A Scaled-up version of the Solar System
If we replace HR8799 with our Sun…
HR8799 is about 2.5 times more massive than our Sun.
Our Solar System Planets
Jupiter
Neptune
Uranus
Saturn
5 AU
30 AU
19 AU
9.5AU
After replacing the central star with our Sun
6.6
31
17
11
Observed HR 8799 planetary system
e
b
c
d
14.5
68
38
24
Against the best model predictions
• We can get spectra of exoplanets now!!
Another Imaged planet around massive star.
• 2008 November
reanalysis of 2003 data
The putative planet was
not visible in early
2009 follow up data!?
β Pictoris b
• about 11 MJupiter
planet orbiting around
a 2.5 Msun star 63
lightyears away.
• Gemini Planet Imager (34 million USD device)
Future
• Simulation of a planet
detected with GPI.
• First light in 2012
• Will look at thousands of
nearby stars
10 yr orbit of a 2 MJupiter
 capable of imaging true
Solar System analogs
(i.e., a Jupiter at 5AU)
a young (100Myr) Sun-like star at 55 Lyrs
James Webb Space
Telescope
• 2018 Launch?
Terrestrial Planet
Finder
• considered two versions
o TPF-C : 3-4 meter
telescope
o TPF-I : 5-6 ~3 meter
telescopes
Demised!!
European version of TPF
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European mission
smaller version of TPF
NASA collaboration
Ended in 2009
Demised also!!
Darwin
Ground-based Observation Only…
• In a coming decade, we will have dozens of (if not hundreds) exoplanet
images
• And, we will have spectra of those exoplanets  able to check their
habitabilities and eventual biosignatures!
40m
European-Extremely Large Telescope
Thirty Meter Telescope
In summary…
Important Concepts
Important Terms
• Images and spectra of exoplanets
are obtainable already!
• Young and nearby stars as best
targets
• Needs for 2nd epoch observation
for confirmation.
• Direct Imaging Detection!
• Adaptive Optics
Chapter/sections covered in this lecture : 11.2
Biosignatures of the Earth : next class
Nulling Interferometry