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

2 High Contrast Imaging Solar observations with a Lyot coronagraph SOHO Coronal mass ejections & sun-grazing comets Planet detections! 16° SOHO C3 coronagraph

3 High Contrast Imaging Stellar coronagraphs Discovery of scattered light disk—  Pictoris Brown dwarfs—GD 229B Smith & Terrile 1984 Science Nakajima et al Nature

4 State of the Art Fomalhaut debris disk F606W + F814W HST/ACS coronagraph –µ ≈ 20 mag arc sec -2 –µ/µ 0 ≈ 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 P Jupiter = 11 years P Neptune = 165 years A census of the outer regions of solar systems (a > 10 AU) is impractical using indirect methods 1/r 2 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 CH 4 and H 2 O opacity at J, H, &, K Burrows Sudarsky & Hubeny 2004 ApJ

10 What is ExAO How can we achieve contrast Q < ? Control of wavefront errors –Wavefront errors,  , cause speckles which masquerade as planets   2 ≈ (Q/16) D 2 [   1 2 ] on spatial frequencies  1 / < f <  2 /   = 3 nm rms for Q = 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 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

12 It’s Not About Strehl 70 nm RMS dynamic wavefront error –S = , 2, & 4 nm RMS static wavefront error –Strehl ratios differ by less than –Systematic errors prevent detection of the exoplanet Atmosphere has ‹  ›=0 –Not crazy to do this from the ground 0 nm2 nm 4 nm 5 M J 1 Gyr exoplanet 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 8-m ExAO Doppler

15 ExAO Science on 8-m Telescopes First reconnaissance of planetary atmospheres T dwarfs Jupiter ExAO Mass Age H2OH2O NH 3

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

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 (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 ≈ 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 T eff, 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 H 2 O and NH 3 clouds

20 The Path to ExAO TMTs 10 4 actuator deformable mirrors 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