1 High Contrast Imaging Extreme AO & 30-m Telescopes James R. Graham UC Berkeley 2005/02/16.
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Transcript of 1 High Contrast Imaging Extreme AO & 30-m Telescopes James R. Graham UC Berkeley 2005/02/16.
1
High Contrast Imaging Extreme AO&
30-m Telescopes
James R. Graham
UC Berkeley
2005/02/16
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High Contrast Imaging
• Solar observations with a Lyot coronagraph
• SOHO• Coronal mass ejections &
sun-grazing comets• Planet detections!
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
http://sohowww.nascom.nasa.gov
16°
SOHO C3 coronagraph
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High Contrast Imaging
• Stellar coronagraphs• Discovery of scattered light
disk— Pictoris• Brown dwarfs—GD 229B
Smith & Terrile 1984 Science 226 1421
Nakajima et al.1995 Nature 378 463
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State of the Art
• Fomalhaut debris disk F606W + F814W HST/ACS coronagraph – µ ≈ 20 mag arc sec-2 – µ/µ0 ≈ 10-10
• Hard-edged Lyot coronagraph
– Contrast is limited by quasi-static wavefront errors• Speckle noise
Kalas Clampin & Graham 2005Nature, Submitted
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Utility of High Contrast Imaging
• Broad potential scientific application– Exoplanet detection– Circumstellar disks
• Proto-planetary & debris disks– Fundamental stellar astrophysics
• Stellar binaries– Mass transfer & loss
• Cataclysmic variables, symbiotic stars & supergiants
– Solar system: icy moons, Titan, & asteroids
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Exoplanet Science
• Doppler surveys have cataloged 137 planets– Indirect searches are hindered by
Kepler’s third law• PJupiter = 11 years
• PNeptune = 165 years
• A census of the outer regions of solar systems (a > 10 AU) is impractical using indirect methods
• 1/r2 dimming of reflected light renders TPF-C insensitive to planets in Neptune orbits
• ExAO is sensitive to self-luminous planets with semimajor axes 4–40 AU
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Architecture of Planetary Systems
• 137 Doppler exoplanets– 5% of targeted stars possess massive planets– Lower limit on occurrence of planets– Abundance of solar systems—why isn’t it 15 to 50%?
• A diversity of exoplanet systems exist…• ≤ 20% of the solar system’s orbital phase space explored
– Is the solar system typical?• Concentric orbits & radial sorting
– What are the planetary systems of A & F stars?– How do planets form? What dynamical evolution
occurs? • Core accretion vs. gravitational collapse• Planetary migration
• Doppler surveys raise new questions– What is the origin of exoplanet dynamical diversity?
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Architecture of Planetary Systems
• Direct imaging is “instant gratification”– Fast alternative to Doppler surveys
• Improved statistics (4–40 AU vs. 0.4–4 AU)– Worst case, dN/d log(a) ~ const.– Oligarchy, dN/d log(a) ~ a
– Searching at large semimajor axis• Sample beyond the snow line• Characterize frequency & orbital geometry > 4 AU
– Is the solar system is unique
• Reveal the zone where planets form by gravitational instability (30–100 AU)
• Uncover traces of planetary migration– Resolve M sin(i) ambiguity
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Cooling Planets
• Contrast required to detect a cooling planet is much less in the near-IR than in the visible– Radiation
escapes in gaps in the CH4 and H2O opacity at J, H, &, K
Burrows Sudarsky & Hubeny 2004 ApJ 609 407
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What is ExAO
• How can we achieve contrast Q < 10-7?
• Control of wavefront errors– Wavefront errors, , cause speckles which
masquerade as planets 2 ≈ (Q/16) D2 [2
2 - 12] on spatial frequencies
1/ < f < 2/ = 3 nm rms for Q = 10-7 between 0.”1 < < 1”
(30 cm to 300 cm)
• Control of diffraction– Need AO & a coronagraph because wavefront
errors and diffraction couple
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Wavefront & Diffraction Control
• Focal plane simulations for Gemini ExAO at H – The dark hole
shows the control radius /2d
• Increasing contrast due to suppression of speckle pinning
Remi Soumier
64 /D
Circular pupil Lyot coronagraph
APLC
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It’s Not About Strehl
• 70 nm RMS dynamic wavefront error – S = 0.93
• 0 , 2, & 4 nm RMS static wavefront error– Strehl ratios differ by less
than 10-4 – Systematic errors prevent
detection of the exoplanet
• Atmosphere has ‹›=0– Not crazy to do this from
the ground
0 nm 2 nm
4 nm
5 MJ 1 Gyrexoplanet
Bruce Macintosh
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ExAO Science on 8-m Telescopes
• ExAOC on 8-m telescopes can yield the first detections of self-luminous exoplanets
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ExAO Science on 8-m Telescopes
• Probe beyond the snow line– Complementary to
Doppler & astrometric searches
8-mExAO
Doppler
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ExAO Science on 8-m Telescopes
• First reconnaissance of planetary
atmospheres
T dwarfs
Jupiter
ExAO
Mas
s
Age
H2O
NH
3
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8-m vs. 30-m
• Better angular resolution
• Better contrast– For a given
rms wavefront error budget (on fixed spatial scales)
• TMT can’t lock on fainter guide stars!
HST
GeminiExAOC
2 = 1.0 arc sec1 = 0.1 arc sec
Jovianreflected light
TMT?
TPF-C?
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TMT Science: What 8-m’s Can’t Do
• Detect Doppler planets /D is too big to find planets in 5 AU orbits– Inner working distance of TMT is three times
smaller
• Reflected light Jupiters– Q ≈ 2 x 10-9 (a/5 AU)-2
– TMT could make old, cold planets a priority– Redundant with TPF-C and indirect searches?
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TMT Science: What 8-m’s Can’t Do
• Explore star forming regions– Taurus, Ophiuchus &c. are
too distant– TMT can work into 5 AU
• Intermediate contrast Q ≈ 10-6 at increased angular resolution (10 mas at H) is valuable– Planet forming environment– Evolved stars and stellar mass loss
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TMT Science: What 8-m’s Can’t Do
• Astrometry– Detection of exoplanet orbital acceleration requires
astrometric precision of about 2 mas (about 1/10 of a pixel for an 8-m)
– Ultimate goal is to measure Keplerian orbital elements, especially e
– Angular resolution of TMT is major benefit for TMT
• Spectroscopy of exoplanet atmospheres– Rudimentary Teff , log (g) measurements at R ≈ 40
are feasible with an 8-m– TMT can study composition of exoplanet
atmospheres, especially important to understand the condensation of H2O and NH3 clouds
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The Path to ExAO TMTs
• 104 actuator deformable mirrors• 5122 fast (kHz), low noise (few e-) CCDs• Fast wavefront reconstructors
– FFT algorithms
• Segment errors & discontinuities must be factored into the wavefront error budget– Discontinuities are OK, so long as the wavefront
sensor is band-limited– AO controls wavefront errors, but not diffraction– Unobscured, filled aperture is ideal…
• Large gaps render apodization problematic• Uniform reflectivity