PowerPoint Presentation

Directly Imaging and Characterizing Extrasolar Planets at High Contrast

Thayne Currie (U. Toronto, NAOJ Aug 2014!)Adam Burrows (Princeton), Nikku Madhusudhan (Cambridge), Ryan Cloutier (U. Toronto) + SEEDS Collaboration1

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Charbonneau et al. (2000)

Mayor and Queloz (1995)

Mayor and Queloz (1995)Extrasolar Planets3Nearly all detected via indirect means. Figures depict two main ones so far: 1) RV, rv wobble induced on star and thus a periodic displacement of stellar spectral lines relative to rest wavelength; shown here are RV data for Alpha Cen Bb, the trend for which the Geneva group model as being due to an earth-mass planet at an orbital separation less than that of Mercury. 2) transit, where planet passes in front of star, causing the star to dim or passes behind the star causing entire system to dim.

MANY Extrasolar Planets

EV

(Oakley & Cash 2009; Kaltenegger et al. 2007)Really want is this. What inner solar system would look like from an alien civilization ~10 pc away in a TPF-like mission. Venus to the right; Earth to the left. And more than that, what we want is this: a spectrum. If we did this for the Earth, in the optical and IR we would see sig of water, oxygen, ozone. Biomarkers: signs that the Earth is not the only planet capable of supporting life. 5Direct Imaging1. Challenges: How to overcome them?

2. What we have learned so far? (e.g. atmospheres)

3. The Near Future?

My talk will open by describing the challenges for directly imaging planets why is this hard? and the advanced observing and image processing techniques that help us finally separate out the stars light from the planets light. What we have discovered about imaged exoplanets has surprised us, in particular the planets atmospheres/sources of emission. Focus on these properties as applied to directly-imaged planetary systems around Fomalhaut and HR 8799. Finally, this is really a field that will explode in the next decade. Describe upcoming facilities like SCExAO and the science enabled with these new facilities.6

Adaptive Optics Sharper Images, Helps Us Separate Planet Light from Starlight(C. Beichman, A. Tanner; Palomar PALM-3K)

Why Directly Imaging Planets is Hard

HR 8799 (Keck/NIRC2 H band; July 2005, Currie et al. 2012a) 1. To understand, image and will sub of smooth seeing halo. 2. quasi-static speckles. 3. important point is that they do not average out. Slowly evolve over time so just taking more images or longer images will not increase SNR.8

Observing Techniques for Imaging Planets:Angular Differential Imaging (ADI) Intuitively know this. If go out to dark sky. Leave camera shutter open get star trails. B/c sky rotates. Normally this is bad: you get image smeared: b/c off-axis objects change in PA.9

(Lafreniere et al. 2007)Post-Processing Techniques for Imaging Planets: A-LOCI (T. Currie 2012, 2013, 2014) A weighted, locally optimized combination of (reference) images (LOCI)

Science ImageRef.ImageweightsGo a step further. Instead of constructing reference PSF from median combination, from weighted linear combination. 11Increased planet throughput, more reliable photometry, (sometimes) slight increase in SNR

Detecting Planets with A-LOCI

12Kalas et al did PSF subtractrion (ref psf star) or roll subtraction (image of same star at different roll angles). Ours more soph. A-LOCI

-subtract image piece at a time. Linear combination of reference images, opti to min. noise (so 'locally optimized comb of images). Coefficients determined within blue regionBig gain- mask subtraction zone, reason is that if planet is there then weights remove planet. But if mask then weights to no-planet- increase throughput, phot reliabiltyDetecting Planets with A-LOCI(T. Currie 2012,2013, 2014)

Truncate elements in covariance matrix during matrix inversion (similar to truncation on # principle components in PCA)``Speckle filteringGo a step further. Instead of constructing reference PSF from median combination, from weighted linear combination. 13

Currie et al. (2012a)Keck/NIRC2 (near-IR), July 2005

Exoplanet Direct Imaging with ADI and A-LOCI (ex. HR 8799)

A-LOCI(May 2012)

14Example with HR 8799 data from summer 2012 paperPSF sub just b and 'sort of' cLOCI bc and d?A-LOCI bcdWith good weather and more comp inc. (bcde)

Keck/NIRC2 (mid IR), November 2012A-LOCI (current)

Exoplanet Direct Imaging with ADI and A-LOCI (ex. HR 8799)

Subaru/IRCS (mid-IR), July 2012 (Currie et al. 2014, in prep.)

VLT/NaCo (near-IR), October 201015Example with HR 8799 data from summer 2012 paperPSF sub just b and 'sort of' cLOCI bc and d?A-LOCI bcdWith good weather and more comp inc. (bcde)

(Marois et al. 2008, 2010; Kalas et al. 2008; Lagrange et al. 2010; Currie et al. 2014a,b; Rameau et al. 2013; Kuzuhara et al. 2013)

Directly Imaged Planetary Systems

HR 8799 bcde

Unpublished

Many candidates to reimage!T. Currie, et al. in progressGet HD 8673 images; HD 95086 b & c images; SAO 206462 images17

Current Limits on Imaging Planets:Young super-jovian planets at > 10 AU(Skemer et al. 2014; Currie et al. 2014 in prep)Architectures of Directly-Imaged Planetary Systems

Two decades ago, knew only about the eight planets in our solar system. Now over 700 planets detected around nearby stars spanning two magnitudes range in mass and semimajor axis. Solar neighborhood is teeming with them. Planets are common (planets form around nearly all young stars); freq of small planets Earths to Super Earths is high.

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A Scaled-Up Version of the Solar System?HR 8799 hotter, more massive and brighter than the Sun

(Marois et al. 2010)

Orbits of Directly-Imaged Planets(Nov. 2009 to Nov. 2012)(Marois et al. 2010; Currie et al. 2012, 2014 in prep.; Mede, Currie et al. 2014 in prep.)Atmospheres of Directly-Imaged PlanetsHR 8799 bcde

ROXs 42Bb

(Currie et al. 2011a, 2014abc)

Directly-Imaged Planets: Should Look like Field Brown Dwarfs?Brown Dwarf Atmosphere Models: similar range in Teff young gas giant planet atmospheres?(Burrows et al. 2006)Near-Infrared Colors of Young Directly-Imaged Planets

Currie et al. (2011a, 2013, 2014)

Fitting HR 8799b and c Data with Standard Atmosphere Models Used for Brown Dwarfs Currie et al. (2011a)FAIL!25

Thicker clouds for Planets (not in Field Brown Dwarfs) = Huge difference

From Atmosphere Models in Currie et al. (2011a)Blackbody envelope primarily affects rel fluxes at 1-3 and 3-5 microns. Water bands of high opacity have low flux densities b/c originate at high altitudes where Temp is low. When clouds are thin optical depth unity achieved at very different altitudes in and out of absorption bands. For fixed observed Teff, thicker clouds translate into hotter Temp profiles (e.g. at given pressure, Temp is higher). Rosseland mean optical depth is higher. Tau = 1 surface becomes more uniform w/ wavelength: spectral features start to wash out.

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HR 8799cYoung Gas Giants have Thick (Patchy?) CloudsCurrie et al. (2011a); Madhusudhan, Burrows, and Currie (2011)

HR 8799bcd(e?) ~ 57 Mj, Teff ~800-1100 K, log(g) ~ 3.8-4.3Best fit to HR 8799 b. Excellent job except at 3.3 micron methane trough. Still tough. Better fit if clouds are patchy. Invoked patchy cloud model. Better fits. Second order effects incl. non-eq carbon chem.27Spectra of Directly-Imaged PlanetsROXs 42Bb (Currie et al. 2014a,b)

Spectra of directly-imaged planets provide further clues. Sigs of CO + H20. Different looking spectrum than field BD. So not only are photometry different spectra are different as well28

Spectra of Directly-Imaged PlanetsH2 Index (2.17-2.24 micron flux ratio) surface gravity tracerLow surface gravity thick clouds?

(Currie et al. 2014a,b; Currie et al. 2011a, 2013)

H2(K)Shape of the spectrum gives clues to the overall appearance of young DI planets. Slope here identified H2(K) slope. Dominant opacity source here is CIA H2. H2 has no permanent dipole and only weak quadrupole moment. But can get temp. dipole moment induced by collisions. For a given metallicity, higher gas density = higher colliisons = higher gravity = plateau at 2.2-2.3 microns. Quantify gravity and compare to everything else. ROXs 42Bb has lowest surface gravity of any MLT dwarf library object except OTS 44, a free floating PMO. ROXs 42Bb like other DI planets has evid. For thick clouds. Low gravity affects vertical mixing in atmosphere and cloud formation. So low g thick clouds?29Direct Imaging in the Near Future: SCExAO Project (2014-)1. Extreme AO imager for Subaru(PI O. Guyon). Strehl Ratio (1.6 mic) ~ 90% 2. Undergoing on-sky testing/engineering runs; full power ~ late 2014?IFU spectrograph (CHARIS)

3. Exoplanet Imaging as follow-on to SEEDS

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What Can SCExAO Do?

15 Myr old; 30 pc awayShows contrast expected for Phase 1 and Phase 2. Phase 1 just CLOWFS (better tip-tilt correction) + PIAA + speckle nulling but at low Strehl (~30%-40%). Phase 2, High Order Pyramid WFS, ~90%+ Strehl. PIAA + VVC, shaped pupil, 8-octant mask. 10x more sensitive than LBT at least. Some delta in camera feeding into PyWFS. Current = performance almost GPI-like. Faster camera, higher Strehl, better than GPI. 31SCExAO vs. First-Light TMT

NFIRAOS estimates from Marois et al. 2012SCExAO: Likely best exoplanet imager in North until 2nd gen TMT (~2030)So why do we want to do this? High-contrast imaging relies on better angular resolution, you get better angular resolution with larger telescopes, why do this when theres the TMT and E-ELT and GMT? Heres the answer. Contrast curve for first-light TMT high-contrast imaging with TMT/IRIS + first light AO system (NFIRAOS). IRIS/NFIROAS designed for studying galaxies, not exoplanets: cannot track telescope pupil (cannot do ADI) + other issues with segmented mirror. Dedicated exoplanet imager is 2nd gen at least. Current timetable? Early 2030s. Now, a lot could change. TMT could wise up. Get better designs. But w/ nominal plan, SCExAO is likely best exoplanet imager in North for next 15-20 years. 32Summary

1. Challenges: How to overcome them?

2. What we have learned so far? (e.g. atmospheres)

3. The Near Future?

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Guyon (2013); Matsuo et al. (2013)Drawn from Gliese catalog, stars within 25 pc. 36SCExAO: A Precursor to TMT Exoplanet ImagingMartinache & Guyon 2011; Jovanovic et al. 2013; Martinache et al. 2014

Speckle Nulling

PIAA Coronagraph planet imaging at ~ lambda/DPIAA - aspheric optics (mirrors or lenses) apodize (or change the shape of) the telescope beam with no loss in throughput. Full 360 deg coverage. Airy rings result from diffraction/edges of pupil, so remap the pupil.

Speckle nulling - Iterative speckle nulling works as follows: in a given image, up to n speckles are identified and their positions marked. With a conventional imaging system, to each speckle position corresponds a two-component (x,y) spatial frequency on the DM, while its brightness indicates amplitude a0 of this spatial frequency. The only real unknown is the phase of each speckle, that can take any value between 0 and 2. In the following four acquisitions, to each speckle is added a speckle probe of same amplitude a0, but each time with a different phase: 0, /2, and 3/2. The intensity of the four speckles resulting from the interference of the original speckle and the probes is used to determine its true phase 0.37

Matsuo et al. (2013)