imaging and characterization of extrasolar planets bruce macintosh james graham steve strom travis...
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3 Known Doppler planetsTRANSCRIPT
Imaging and characterization of extrasolar planets
Bruce MacintoshJames Graham
Steve Strom
Travis Barman, Lisa Poyneer, Mitchell Troy, Mike Liu, Stan Metchev
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Outline
• Science motivation and expected landscape in 2015• Four key science missions
– Robust statistical sample of giant extrasolar planets– Characterization of extrasolar planet atmospheres and abundances– Studies of circumstellar debris disks– Detection of young planets and protoplanetary disks
• Comparisons: 8 vs 30 vs 50 m• Brief discussion of space missions• Excessive generalizations and conclusions
• Missing: Mid-IR spectroscopy and imaging, Doppler, transit characterization…
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Known Doppler planets
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Predicting Exoplanet Research in 2016
Key question: how do solar systems form?
• What are the physical conditions in planet forming disks?– What are the heating & cooling processes in disks?– What is the origin of viscosity?– How do condensates grow & what is the particle size spectrum vs. time?– What is the nature of disk-planet interactions?
• What are the relative roles of global gravitational instability & core accretion?
– Can core-accretion form super-Jupiters?– Can Jovian planets form in inner disks (< 5 AU)?– What is the relation between Jovian & terrestrial planet formation?
• Early disk-planet evolution?– What is the accretion rate onto a protoplanet?– What role do density waves and gaps play in controlling planet growth?– What controls dissipation & dispersal of disks?– How and when does migration occur?
• What can the properties of exoplanets tell us about their formation history?
• With GSMT, these questions can be studied through studying planet populations as a function of age
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Direct detection in the next decade
• Conventional AO– Detect hot very young (<20 Myr) planets in wide
(>50 AU) orbits• Extreme AO on 8-m telescopes (Gemini,
VLT + others): 2010– Direct detection of warm self-luminous planets
(selects for (<1 Gyr) and massive)– Probes outer parts of target systems– Low-res (40-100) spectroscopic characterization
• Interferometry – 5-micron emission (LBT)– Differential phase / astrometry (VLT, Keck)– Small number of target systems
• Space: – TPF no earlier than 2020– Possible 2-m-class Jovian planet imagers
20-sec. Gemini Planet Imager 5 MJ/200 Myr planet @ 0.6
arcseconds
VLT/NACO 5 MJ / 8 MYr
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Cooling extrasolar planets
Current AO 0.5-2”
8-m Extreme AO 0.2-1”
30-m Extreme AO 0.06-1”
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Monte Carlo planet population: GPI
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Detected planets for I<8 mag Gemini Planet Imager field survey
Gemini Planet Imager field survey completeness contours
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Four key science missions and requirements
1. Detect and characterize a large sample of extrasolar planets (Teff, R, g)• Overlap with Doppler is
desirable
2. High-SNR spectroscopy of planets (abundances)
3. Detection of planets in the process of formation and shortly after (1-30 Myr)
4. Studies of circumstellar dust on AU scales
10-8 @ 50 mas, I<8 magR~100 spectroscopyHundreds of planets and
thousands of targets
R~1000 spectroscopy
10-6 @ 30 mas, H<10 IR WFS, Polarimetry
Polarimetry 2”+ FOV
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Modeling and assumptions
• Three simulation levels• “Full AO” simulations
– No assumptions other than Taylor frozen-flow/multilayer atmospheres
– AO, DM control loop dynamics– Primary mirror effects– Exposure times <5 seconds– Code limited to 30-m case– Various coronagraphs possible
• Monte Carlo simulations– “Generic” AO system– Statistical assumptions about atmosphere
speckle lifetimes derived from Full AO sims– Exposure time up to several minutes– Used for 30, 50, 99-m case– Nonphysical ideal apodizer coronagraph
• Analytic error budgets– Used to evaluate long-exposure static effects
• Contrast varies strongly with star brightness, instrument architecture, etc.
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ExAO contrast noise sources
Inner working angle2-5 /D
Speckle contrast1/(D2 t1/2)
Photon contrast1/(D2 t1/2 )
Systematic/static contrastWeak D, t dependence
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Comparison between 30 and 50 m
1 AU
5 AU
0.1 AU G5 star @ 10 pc
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Equivalent to a factor of 8 exposure time + factor of 2 better control of static errors
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Overlap with Doppler searches
3/D (30m)3/D (50m)
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Planetary Spectroscopy
• Composition is destiny– The zero-temperature
equilibrium radius is determined by the chemical composition
• Composition is a primary window on the formation of the planets in the solar system
– Order of magnitude range in abundances from planet to planet, e.g., C ranges from x3 (Jupiter) – x30 (Uranus/ Neptune)
– Jovian abundances rule out formation by gravitational collapse
Zapolsky & S
alpeter 1965
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Spectral characterization: R=100 for Teff and gravity/mass
• Differential exoplanet spectra indicate that R ≈ 100 is suitable for measuring atmospheric parameters
– [1.5] - [1.6] is a good effective temperature indicator
– [1.5] – [2.2] is a good gravity indicator
– Higher spectral resolution may address composition of hot Jupiters
Spectra are calculated using fully self-consistent models with the PHOENIX atmosphere code
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Spectral characterization: R=100 for Teff and gravity/mass
• Differential exoplanet spectra indicate that R ≈ 100 is suitable for measuring atmospheric parameters
– [1.5] - [1.6] is a good effective temperature indicator
– [1.5] – [2.2] is a good gravity indicator
– Higher spectral resolution may address composition of hot Jupiters
Spectra are calculated using fully self-consistent models with the PHOENIX atmosphere code
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Planets discovered by a ExAO field survey: 30 vs 8 m
T dwarfs
Jupiter
Mas
s
Age
30-m
8-m
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Spectral characterization: R=1000 for composition
• High spectral resolution shows individual molecular features at R=1000
• Features are much stronger in cool planets
• This opens up the possibility of directly probing (atmospheric) composition
800 K
800 K
500 K
400 K
300 K
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Spectroscopic sensitivity
G5 star @ 10 pc
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Planet formation
• A survey of young stars will show when & where planets form– Detection of young Jovian planets in situ is evidence for core accretion– Planets in circular orbits in young systems (~ 10 Myr) at large semimajor axis
separation must have formed by gravitational instability– Co-existence of planets & disks will illuminate disk-planet interactions
• Planet formation & survival in multiple star systems and stellar clusters– Does disk disruption in binaries prevent planet formation?– When is photoevaporation of disks important?– Tidal stripping in dense clusters?
• Requires very small inner working distance• Complex systems with planets and disks - polarimetry?
T Tauri star, 150 pc with 3 MJ companion in optically thick disk
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Accretion history of planets determines luminosity later in life
• In different formation scenarios, planets will have complex luminosity histories
1. Runaway dust accretion then exhaustion of solid material
2. Slow gas accretion3. Runaway gas accretion
until growth is shut off by opening of gap in disk or dissipation of nebula
• Each phase will have a distinct radiative signature
• Initial conditions influence future evolution
Hubickyj et al. 2005, Icarus, in press
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Accretion history of planets determines luminosity later in life
• In different formation scenarios, planets will have complex luminosity histories
1. Runaway dust accretion then exhaustion of solid material
2. Slow gas accretion3. Runaway gas accretion
until growth is shut off by opening of gap in disk or dissipation of nebula
• Each phase will have a distinct radiative signature
• Initial conditions influence future evolution
Fortney et al. 2005, PPV
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2
3
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Key parameter is Inner Working Angle => /D
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Comparison: 30 vs 50 m for young systems
• 3 /D on an obscured aperture requires advanced/complicated coronagraphs
– Shearing nulling interferometer (low throughput)
– Pupil remapping (unproven)– Phase / diffraction cancellation
(half field of view, chromatic)• 5 /D can be achieved with
conventional coronagraphs
• Very challenging for <30m• Reduced technological risk
on 50-m• Alternatively, 50-m can study
these scales at longer wavelengths
Stop
Starlight frompre- AO
Mach-ZenderNuller (DSS)
DeformableMirror
Modulator
DM Controller
WFS Camera
Processor
Science IFU
SpatialFilter
TMT shearing interferometer + 2 hour
sensitivity map
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Circumstellar dust disks
• Dust disks in other solar systems are an important part of planetary systems
• Structure in dust can trace planets that are too low-mass to be detected
• GSMT may be able to access Zodiacal dust analogs
– Current debris disks are Kuiper belts
• More modeling is needed but also very challenging 100 Myr solar system model
(Metchev, Wolf) with ~10-3.5 at 130 pc from Keck NGAO
study
• Debris disks are primarily diffuse structures– Sensitivity does not necessarily improve with angular resolution– Sensitivity is limited by systematic errors / PSF subtraction artifacts– High Strehl well-known PSF is more important than aperture
AU Mic debris diskUH 2.2m: R-band (0.6 um)
100 AUKalas, Liu & Matthews (2004)
Keck 10-m AO: H-band (1.6 um)0.04” FWHM = 0.4 AU
Liu(2004)
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TPF JPF
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Conclusions
• This area is extremely speculative: we don’t yet know the limits of ExAO on 8-m
• Detection of Jovian planet population– Telescope aperture determines survey time and survey size– Larger telescopes have greater overlap with Doppler surveys
• Characterization of Jovian planets– R=100 spectroscopy can determine macroscopic properties– R=1000 can determine abundances but is photon-starved
• In situ observations of planet formation– Unique capability of extremely large ground-based telescopes– Requires inner working angles ~0.03 arcseconds at moderate
contrast– For a 30-m, requires an advanced (unproven) coronagraph– For a 50-m, more straightforward
• Debris disk science– Important; needs modeling; independent of aperture