Project Title PLANETS Title of Deliverable Planets Testbed ...
Direct Imaging Of Planets - Princeton Universitygk/A205OLD/lecture11.pdf · 2003. 10. 20. ·...
Transcript of Direct Imaging Of Planets - Princeton Universitygk/A205OLD/lecture11.pdf · 2003. 10. 20. ·...
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Direct Imaging Of Planets
AST 205David Spergel
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Advantages
•Much faster detections
•Immediate detection of entire system
•Enormous additional science
•Size and Albedo
•Spectroscopy
•Biomarkers
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Why is this hard?• Detecting light from planets
beyond solar system is hard:– Planet signal is weak but
detectable (few photons/sec/m2)
– Star emits million to billionmore than planet
– Planet within 1 AU of star– Dust in target solar system ¥300
brighter than planet• Finding a firefly next to a
searchlight on a foggy night
>109>106
ScatteredLight
ThermalEmission
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Fourier Transform
Any function can berepresented as a sum ofcosine (and sine) waves
=
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Telescope Size Sets Resolving Power
q = l/d
d=1
d=2
d=4
Ringing
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Airy Rings
Linear Scale
Log Scale(1e-10 is black)
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The Diffraction Problem(Visible)
Focal plane
Diameter (D)
The image in thefocal plane is thespatial Fouriertransform of theentrance field
Wavelength (l)
Entrance Pupil
0 5 10 1510-12
10-10
10-8
10-6
10-4
10-2
100
Angle (lambda/D)
1
1e-10
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Pupil Coronagraph
What if we don’tgive equal weight toeach Fourier mode?
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Pupil Design
Concentric Rings
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Starshaped Mask
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Starshaped mask
20-point star
150-point star
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Wavefront Sensing andControl
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What is the biggest problem?
Surface Errors Variations in Reflectivity
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Interferometery
• Enables precision astrometry,high resolution imaging,starlight nulling
• Make astrometric census of planets • Detect “Hot Jupiter’s” • Detect exo-zodiacal dust clouds• Image protostellar disks
• Break link between diameter, baseline
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IRInterferometer
• Interferometer with cooled two to four 3~4 mmirrors– 30 m boom– 75-1000 m baseline using formation flying
• Operate at 1 AU for 5 years to survey 150 stars
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Nulling Interferometryl /b
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2-arm Nulling Interferometerb
y
x
Null depth integrated overfinite star diameter ~8x10-5
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4-arm Nulling InterferometerIntensity:
b
y
x
Null depth integrated overfinite star diameter ~6x10-10
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InterferometerDetects and
CharacterizesPlanetary Systems
• TPF produces image of planetarysystem
– Orbital location– Temperature and radius
• TPF produces spectrum to searchfor biomarkers• 1-2 m telescopes to find Jupiters,nearest Earths•3-4 m telescopes for full TPF goals
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The Angular Resolution Challenge
+
• Coronagraphs at >3l/D• Interferometers at > 1 l/B
10 mm, 28 mCoronagraph
Cost ($$), L
aunc h Dat e
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Conclusions
• Interferometry and Coronagraphy are twopromising but difficult techniques
• They have the potential of yielding directdetections of Earth-like planets
• Planets can not only be detected but alsocharacterized