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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