High Contrast Imaging Extreme AO & 30-m Telescopes

1. High Contrast Imaging Extreme AO&30-m Telescopes James R. Graham UC Berkeley 2005/02/16

2. High Contrast Imaging SOHO C3 coronagraph • Solar observations with a Lyot coronagraph • SOHO • Coronal mass ejections & sun-grazing comets • Planet detections! 16° http://sohowww.nascom.nasa.gov

3. 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

4. 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

5. 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

6. 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

7. 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?

8. 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

9. 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

10. 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 [22 - 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

11. 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

12. 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 5 MJ 1 Gyr exoplanet 4 nm Bruce Macintosh

13. ExAO Science on 8-m Telescopes • ExAOC on 8-m telescopes can yield the first detections of self-luminous exoplanets

14. ExAO Science on 8-m Telescopes • Probe beyond the snow line • Complementary to Doppler & astrometric searches Doppler 8-m ExAO

15. ExAO Science on 8-m Telescopes T dwarfs • First reconnaissanceof planetary atmospheres Age Mass NH3 H2O ExAO Jupiter

16. 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 Gemini ExAOC TMT? Jovian reflected light TPF-C? 2 = 1.0 arc sec 1 = 0.1 arc sec

17. 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?

18. 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

19. 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

20. 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