High Contrast Imaging Extreme AO

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High Contrast Imaging Extreme AO30-m Telescopes

• James R. Graham
• UC Berkeley
• 2005/02/16

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High Contrast Imaging
SOHO C3 coronagraph

• Solar observations with a Lyot coronagraph
• SOHO
• Coronal mass ejections sun-grazing comets
• Planet detections!

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http//sohowww.nascom.nasa.gov
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High Contrast Imaging

• Stellar coronagraphs
• Discovery of scattered light disk? Pictoris
• Brown dwarfsGD 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 2005 Nature, 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 Keplers third
  law
• PJupiter 11 years
• PNeptune 165 years
• A census of the outer regions of solar systems (a
  gt 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 440 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 systemswhy isnt it 15 to
  50?
• A diversity of exoplanet systems exist
• 20 of the solar systems 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 (440 AU vs. 0.44 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 gt 4 AU
• Is the solar system is unique
• Reveal the zone where planets form by
  gravitational instability (30100 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 lt 10-7?
• Control of wavefront errors
• Wavefront errors, ??, cause speckles which
  masquerade as planets
• ?? 2 (Q/16) D2 ?22 - ?12 on spatial
  frequencies ?1/? lt f lt ?2/?
• ?? 3 nm rms for Q 10-7 between 0.1 lt ? lt 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
64 ?/D

• Focal plane simulations for Gemini ExAO at H
• The dark hole shows the control radius ?/2d
• Increasing contrast due to suppression of
  speckle pinning

Circular pupil
Lyot coronagraph
APLC
Remi Soumier
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Its 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
5 MJ 1 Gyr exoplanet
4 nm
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

Doppler
8-m ExAO
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ExAO Science on 8-m Telescopes
T dwarfs

• First reconnaissance of planetary atmospheres

Age
Mass
NH3
H2O
ExAO
Jupiter
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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 cant lock on fainter guide stars!

HST
Gemini ExAOC
TMT?
Jovian reflected light
TPF-C?
?2 1.0 arc sec ?1 0.1 arc sec
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TMT Science What 8-ms Cant 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-ms Cant 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-ms Cant 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