Exoplanets:direct detection

ASTR 1420

Lecture 17

Sections 11.2

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

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

sensitivity curve

4

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!!!

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

• Actual Example from Keck AO

Need for a confirmation!

Some early discoveries…• European Very Large Telescopeo 2M1207b central obj is a brown dwarfo AB Pic B companion is a BDo GSC 8047-0232 B companion is a BD

AB Pic B GSC 8047-0232 B

2M1207b

Recent Discoveries• 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

C. Marois, B. Macintosh, T. Barman, B. Zuckerman, Inseok Song, J. Patience, D. Lafreniere, R. Doyon

Direct Imaging of Planetary System!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…

Our Solar System Planets

Jupiter Neptune Uranus Saturn

5 AU 30 AU 19 AU 9.5AU

Observed HR 8799 planetary system

e b c d

14.5 68 38 24

After replacing the central star with our Sun

6.6 31 17 11

HR8799 is about 2.5 times more massive than our Sun.

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.

Future• Gemini Planet Imager (34 million USD device)

• Simulation of a planet detected with GPI.

• First light in 2012

• Will look at thousands of nearby stars

capable of imaging true Solar System analogs (i.e., a Jupiter at 5AU)

10 yr orbit of a 2 MJupiter

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!!

Darwin• European mission• smaller version of TPF• NASA collaboration• Ended in 2009

European version of TPF

Demised also!!

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!

Thirty Meter Telescope

European-Extremely Large Telescope

40m

In summary…

Important Concepts• Images and spectra of exoplanets

are obtainable already!• Young and nearby stars as best

targets • Needs for 2nd epoch observation

for confirmation.

Important Terms• Direct Imaging Detection!• Adaptive Optics

Chapter/sections covered in this lecture : 11.2Biosignatures of the Earth : next class

Nulling Interferometry