Download Imaging and characterization of extrasolar planets Bruce Macintosh

Imaging and characterization of
extrasolar planets
Bruce Macintosh
James Graham
Steve Strom
Travis Barman, Lisa Poyneer, Mitchell Troy, Mike Liu, Stan Metchev
Outline
• Science motivation and expected landscape in 2015
• Four key science missions
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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?
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What are the physical conditions in planet forming disks?
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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?
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Early disk-planet evolution?
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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
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Conventional AO
– Detect hot very young (<20 Myr) planets in wide
(>50 AU) orbits
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VLT/NACO 5 MJ / 8 MYr
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
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Interferometry
– 5-micron emission (LBT)
– Differential phase / astrometry (VLT, Keck)
– Small number of target systems
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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
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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)
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Overlap with Doppler is
desirable
 10-8 @ 50 mas, I<8 mag
R~100 spectroscopy
Hundreds of planets and
thousands of targets
2. High-SNR spectroscopy of
planets (abundances)
 R~1000 spectroscopy
3. Detection of planets in the
process of formation and
shortly after (1-30 Myr)
 10-6 @ 30 mas, H<10 IR WFS,
Polarimetry
4. Studies of circumstellar dust
on AU scales
 Polarimetry 2”+ FOV
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Modeling and assumptions
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Three simulation levels
“Full AO” simulations
– No assumptions other than Taylor frozenflow/multilayer atmospheres
– AO, DM control loop dynamics
– Primary mirror effects
– Exposure times <5 seconds
– Code limited to 30-m case
– Various coronagraphs possible
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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
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Analytic error budgets
– Used to evaluate long-exposure static effects
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Contrast varies strongly with star
brightness, instrument architecture, etc.
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ExAO contrast noise sources
Inner working angle
2-5 l/D
Speckle contrast
1/(D2 t1/2)
Photon contrast
1/(D2 t1/2 Dl)
Systematic/static contrast
Weak D, t dependence
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Comparison between 30 and 50 m
G5 star @ 10 pc
0.1 AU
1 AU
5 AU
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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
3l/D (50m)
3l/D (30m)
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Planetary Spectroscopy
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Composition is destiny
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Composition is a
primary window on the
formation of the planets
in the solar system
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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 & Salpeter 1965
– The zero-temperature
equilibrium radius is
determined by the
chemical composition
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Spectral characterization: R=100 for Teff
and gravity/mass
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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 selfconsistent 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 selfconsistent models with the PHOENIX
atmosphere code
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Planets discovered by a ExAO field
survey: 30 vs 8 m
T dwarfs
30-m
8-m
Jupiter
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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
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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
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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
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In different formation
scenarios, planets will
have complex luminosity
histories
1. Runaway dust accretion
then exhaustion of solid
material
2. Slow gas accretion
3. Runaway gas accretion
until growth is shut off by
opening of gap in disk or
dissipation of nebula
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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
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In different formation
scenarios, planets will
have complex
luminosity histories
1. Runaway dust accretion
then exhaustion of solid
material
2. Slow gas accretion
3. Runaway gas accretion
until growth is shut off
by opening of gap in
disk or dissipation of
nebula
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Each phase will have a
distinct radiative
signature
Initial conditions
influence future
evolution
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Fortney et al. 2005,
PPV
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Key parameter is Inner Working Angle => l/D
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Comparison: 30 vs 50 m for young
systems
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3 l/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)
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Deformable
Mirror
Starlight from
pre- AO
Mach-Zender
Nuller (DSS)
Modulator
Stop
Spatial
Filter
5 l/D can be achieved with
conventional coronagraphs
WFS Camera
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Very challenging for <30m
Reduced technological risk
on 50-m
Alternatively, 50-m can study
these scales at longer
wavelengths
Sc ienc e IFU
TMT shearing
interferometer + 2 hour
sensitivity map
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Circumstellar dust disks
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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
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More modeling is needed but also
very challenging
100 Myr solar system model
(Metchev, Wolf) with t~10-3.5
at 130 pc from Keck NGAO
study
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AU Mic debris disk
UH 2.2m: R-band (0.6 um) Keck 10-m AO: H-band (1.6 um)
0.04” FWHM = 0.4 AU
100 AU
Kalas, Liu & Matthews (2004)
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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
Liu(2004)
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
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