Prospects for detection of protoplanets

Prospects for the Detection of Protoplanets
[Review]
Sebastian Wolf
Emmy Noether Research Group
“Evolution of Circumstellar Dust Disks to Planetary Systems”
Max Planck Institute for Astronomy
discs06 – Cambridge, UK [July 20, 2006]
Planet Formation in a Nutshell
Theory
Star Formation Process
(sub)µm
Circumstellar Disks
Planets
particles
• Brownian Motion, Sedimentation, Drift
• Inelastic Collision => Coagulation
cm/dm grains
• Agglomeration;
Fragmentation
Planetesimales
• Gravitational Interaction: Oligarchic Growth
Planets (cores)
• Gas Accretion
(Waelkens 2001)
Alternativ: Gravitational Instability
Giant Planet
how to identify
IRAS 04302+2247
Grain Growth?
• SED: (sub)mm slope
• Shape of ~10μm silicate feature
• Scattered light polarization
(e.g., spectro-polarimetry)
HK Tau
• Multi-wavelength imaging
+ Radiative Transfer Modelling
The “Butterfly Star” in Taurus
Wolf, Padgett, & Stapelfeldt (2003)
IRAS 04302+2247
HK Tau
IRAS 04302+2247
The “Butterfly Star” in Taurus
submm-sized grains in the disk midplane,
~
AU
60
0
HK Tau
IRAS 04302+2247
Wolf, Padgett, & Stapelfeldt (2003)
instellar-like grain size in the circumstellar envelope
4.
3”
IRAS 04302+2247
Size Scales
Solar System
Angular diameter of the orbit of solar system planets
in a distance of the Taurus star-forming region (140pc)
Neptune
Jupiter
Earth
- 429 mas
- 74 mas
- 14 mas
Mid-infrared interferometric spectroscopy Dust processing in the innermost regions
MIDI setup
[Leinert et al. 2004]
Mid-infrared interferometric spectroscopy Dust processing in the innermost regions
Silicate Feature
[Leinert et al. 2004]
Effect also found in disks around TTauri Stars - (Schegerer & Wolf, in prep.)
Finding Planets – In Disks?!
UV – (N)IR
Additional Problems
(Dust...)
IR – mm
Young disks
Scattering
Thermal Reemission
Extinction
(Inclination-dependent)
Dust parameters, T(r,θ,φ), ρ(r,θ,φ)
Response of a gaseous, viscous
protoplanetary disk to an embedded planet
Disk surface densities for planets with masses 1, 0.1, and 0.01MJ orbiting a 1Msun star
[see also Bryden et al. 1999, Kley et al. 2001, Lubow et al. 1999,
Ogilvie & Lubow 2002, D‘Angelo et al. 2003, Winters et al. 2003]
(Bate et al. 2003)
0.01 MJ
0.03 MJ
0.3 MJ
1 MJ
(Bate et al. 2003)
Is this what
we have to
look for?
[ G. Bryden ]
Jupiter
in a 0.05 Msun disk
around
a solar-mass star
as seen with ALMA
d=140pc
Baseline: 10km
λ=700μm, tint=4h
(Wolf et al. 2002)
inclination = 5°
Scattered light images
λ = 1.14μm
Gap width (FWHM): ~ 1 AU.
[7 AU × 7 AU].
based on 2D density
distributions resulting from
hydrodynamics simulations
vertical structure is
assumed to be Gaussian
with a scale height that
varies as a power law with
radius (i.e., a flared disk)
inclination = 70°
no gap
gap
[ 2MJ planet at 1 AU ]
[ no planet ]
Log( Disk surface brightness)
[Varniere et al. 2006]
Azimuthally averaged optical surface
brightness profiles for a disk with /
without an embedded planet.
2MJ planet
at 1 AU
Decrease in the surface brightness
profile near the planet
Bright bump in the profile at the outer
edge of the gap
[ Varniere et al. 2006 ]
Richling (in prep.): Observability of gaps depending on wavelength + viewing angle
(based on irradiated α-disk models)
Steinacker & Henning (2003): Analysis of the spectral appearance of gaps
Wilner et al. 2004: Observations of the inner disk structure
with the Square Kilometer Array (Science Case Study)
Small-scale spirals encircling the planet
(detached from the global spiral)
=
Feature of a circumplanetary disk
Gaps
in young disks
In the vicinity
of the planet
Zoom in onto the planet: Disk surface densities for a planet with a mass of 0.5MJ orbiting a 1Msun star.
Plus signs: Lagrange points. Overplotted curve: Roche lobe. (D‘Angelo et al. 2002)
Is this what we have to look for?
Density distribution in the midplane
of the circumstellar disk with
an embedded massive planet.
Can we map young giant
planets?
Close-up view:
Planetary region
Procedure
Density Structure
(2D Hydrosimulation)
Stellar heating
(3D Radiative transfer)
Planetary heating
(3D Radiative transfer)
Prediction of Observations
Wolf & D’Angelo (2005)
Close-up view:
Planetary region
Mplanet / Mstar = 1MJup / 0.5 Msun
50 pc
Orbital radius: 5 AU
Disk mass as in the circumstellar
disk as around the Butterfly Star
in Taurus
Maximum baseline: 10km,
900GHz, tint=8h
100 pc
Wolf & D’Angelo (2005)
Random pointing error during the observation: (max. 0.6”) ;
Amplitude error, “Anomalous” refraction;
Continuous observations centered on the meridian transit;
Zenith (opacity: 0.15); 30o phase noise;
Bandwidth: 8 GHz
Close-up view:
Planetary region
1.
The resolution of the images to be obtained
with ALMA will allow detection of the warm dust
in the vicinity of the planet only if the object
is at a distance of not more than about 100 pc.
For larger distances, the contrast between
the planetary region and the adjacent disk in all
of the considered planet/star/disk configurations
will be too low to be detectable.
2.
Even at a distance of 50 pc, a sufficient resolution
to allow a study of the circumplanetary region
can be obtained only for those configurations with
the planet on a Jupiter-like orbit but not when
it is as close as 1 AU to the central star.
3.
The observation of the emission from the dust
in the vicinity of the planet will be possible only
in the case of the most massive, young
circumstellar disks we analyzed.
50 pc
100 pc
Wolf & D’Angelo (2005)
Strong spiral shocks near the planet are able
to decouple the larger particles (>0.1mm)
from the gas
Gaps
=>
formation of an annular gap in the dust,
even if there is no gap in the gas density
(example: gap in 1mm grains opened by a 0.05MJup planet)
in young disks
two-fluid simulations
PaardeKooper & Mellema (2004)
Imaging in the Mid-infrared (~10micron)
Hot Accretion Region
around the Planet
10μm surface brightness
profile of a T Tauri disk with
an embedded planet ( inner
40AUx40AU, distance:
140pc)
[Wolf & Klahr, in prep.]
i=0deg
i=60deg
Science Case Study for T-OWL:
Thermal Infrared Camera for OWL (Lenzen et al. 2005)
Justification of the Observability in the Mid-IR
for nearby objects (d<100pc)
T-OWL
Thermal Infrared Camera for OWL
5 AU
10 pc
30 pc
70 pc
Wolf, Klahr, Egner, et al. 2005 in Lenzen et al. 2005
MATISSE
Multi AperTure Mid-Infrared SpectroScopic Experiment
High-Resolution Multi-Band Image Reconstruction
+ Spectroscopy in the Mid-IR
Proposed 2nd Generation VLTI Instrument
Specifications:
• L, M, N, Q band: ~2.7 – 25 μm
• Spectral resolutions: 30 / 100-300 / 500-1000
• Simultaneous observations in 2 spectral bands
What’s new?
• Image reconstruction
on size scales of 3 / 6 mas (L band) 10 / 20mas (N band) using ATs / UTs
• Multi-wavelength approach in the mid-infrared
3 new mid-IR observing windows for interferometry (L,M,Q)
• Improved Spectroscopic Capabilities
MATISSE
MATISSE
Precursor of Darwin in terms of image reconstruction;
Experience (MIDI + AMBER)
What is the status of “disk
clearing” in the inner few AU?
Sublimation radius ~ 0.1-1AU (TTauri HAe/Be stars)
but:
Observations: Significant dust depletion >> Sublimation Radii
TW Hydrae (10Myr): ~ 4 AU (Calvet et al. 2002)
GM Aur: ~ 4 AU (Rice et al. 2003)
CoKu Tau/4: ~10 AU (D’Alessio et al. 2005, Quillen et al. 2004)
10μm image of a circumstellar disk with an inner hole, radius 4AU
(inclination: 60deg; distance 140pc; inner 60AU x 60AU)
Constraints on a planetary origin for the gap
in the protoplanetary disc of GM Aurigae
increasing planetary mass
Azimuthally averaged mid-plane density
profiles for substellar objects (planets).
The SED of GM Aur computed using azimuthally
averaged density profiles.
• A ~ 2 MJ planet, orbiting at 2.5 AU in a disk with mass 0.047 M and radius 300 AU,
provides a good match both to the SED and to CO observations which constrain
the velocity field in the disc.
• A range of planet masses is allowed by current data, but could in principle
be distinguished with further observations between 3 and 20 μm.
Rice et al. (2003)
Imaging in the
Nearinfrared
Jupiter @ 5AU
Solar-type central
star
2.2 micron
(scattered
stellar light)
AB Aurigae - Spiral arm structure
(Herbig Ae star; H band; Fukagawa, 2004)
Inner disk
Young disks
(< a few AU)
Which disks to study?
Etc. ...
Clearly identified disks, well studied, but …
potentially ”planet-building sites” well hidden…
Preparatory
studies,
concentrating on
face-on disks
Useful
techniques:
Coronography;
Differential
polarimetric
imaging;
Very distant …
AB Aurigae
HD 100546
(Grady 2001 / 2003)
high-resolution
mm maps
inner ~12 AU
Influence on the
Net - SED
Inner Disk
Wolf & D’Angelo (2005)
inner ~12 AU
Influence on the
Net - SED
Planet
Wolf & D’Angelo (2005)
inner ~12 AU
Influence on the
Net - SED
Planetary
Environment
Wolf & D’Angelo (2005)
inner ~12 AU
Influence on the
Net - SED
Inner Disk
+
Planet
+
Planetary
Environment
Wolf & D’Angelo (2005)
No significant
effect on the
Net SED
Influence on the
Net - SED
Planetary Contribution (direct or scattered radiation, dust reemission)
< 0.4%
Disk reemission (inner 12 AU)
(depending
on the
particular
model)
Planetary radiation significantly affects the dust reemission SED
only in the near to mid-infrared wavelength range.
This spectral region is influenced also by the warm upper layers of the
disk and the inner disk structure, the planetary contribution.
=> The presence of a planet + the temperature / luminosity
of the planet cannot be derived from the SED alone.
In the case of a more massive planet / star the influence of the planet is
even less pronounced in the mid-infrared wavelength range (lower
luminosity ratio LP / L*).
see also Varniere et al. (2006)
High-Spatial
Resolution
Spectroscopy
Spectroscopic
verification
of gaps through
their dynamics
R ~ 105,
λ ~ 5-30μm
GSMT Science Case Study
[ www.aura-nio.noao.edu ]
MHD simulations:
Internal Stress arises self-consistently from
turbulence generated by magnetorotational
instability (‚MHD turbulence‘)
>>> gaps are shallower and
asymmetrically wider
>>> rate of gap formation is slowed
Gaps
in young disks
-
MHD
simulations
(Winters et al. 2003; see also Nelson & Papaloizou 2003)
Sources of Astrometric Wobble
1. Planet’s Gravitational Pull
2. Disk’s Gravitational Pull
3. Disk’s Photospheric Signal
(center-of-light wobble)
(G. Bryden, priv. comm.)
Center-of-Light-Wobble
(G. Bryden, priv. comm.)
Protoplanetary Disks evolve …
• Near-infrared photometric studies:
sensitive to the inner ~ 0.1 AU around solar-type stars:
• Excess rate decreases from ~80% at an age of ~1 Myr
to about 50% by an age of ~3 Myr (Haisch et al.~2001)
• By ages of ~10-15 Myr, the inner disk has diminished to nearly zero
(Mamajek et al.2002).
• Far-infrared / millimeter continuum observations
probe the colder dust and thus the global dust content in disks:
• Beckwith et al. (1990): no evidence of temporal evolution in the mass
of cold, small (<1mm) dust particles between ages of 0.1 and 10Myr
• By an age of 300 Myr the dust masses were found to by decreased
by at least 2 orders of magnitude (Zuckerman & Becklin 1993).
• Based on studies with the Infrared Space Observatory (ISO), the disk fraction
amounts to much less than 10% for stars with ages > 1 Gyr
(e.g., Spangler et al. 2001; Habing et al. 2001; Greaves et al. 2004;
Dominik & Decin 2003).
… but still the disk may outshine the planet.
• The exozodiacal dust disk around a target star, even at solar level,
will likely be the dominant signal originating from the extrasolar system:
• Solar system twin: overall flux over the first 5 AU is about 400 times larger
than the emission of the Earth at 10μm
• Zodiacal light of our own solar system:
• potential serious impact on the ability
of space-born observations (e.g. DARWIN)
• attributed to the scattering of sunlight
in the UV to near-IR, and the thermal dust
reemission in the mid to far-IR
• > 1micron: signal from the zodiacal light
is a major contributor to the diffuse sky
brightness and dominates the mid-IR sky
in nearly all directions, except for very low
galactic latitudes (Gurfil et al. 2002).
betaPic
Young disks / Debris disks
Planet Ù Disk interaction
IRAS 04302+2247
AUMic
Young circumstellar
disks around T Tauri /
HAe/Be stars
Debris disks
optically thick
optically thin
HK Tau
Density structure dominated by
BD+31643
Gravitation
+
Gas dynamics
Radiation Pressure
Poynting-Robertson
effect
Scattered light
images (optical)
Characteristic Debris
Disk Density Patterns
A planet, via resonances and
gravitational scattering
produces
[1]
An asymmetric resonant dust belt
with one or more clumps,
intermittent with one or a few offcenter cavities, and
[2]
A central cavity void of dust.
Simulated surface density of circumstellar dust captured into
particular mean motion resonances
(Ozernoy et al. 2000)
Resonant structures can serve
as indicators of a planet in a
circumstellar disk
[1] Location
[2] Major orbital parameters
[3] Mass of the planet
(static)
equilibrium
density
distribution
Scattered Light Image
104 particles
107 particles
dynamical simulation
• ~ 104 massless particles
• gravitational intercation with planet + star
• Poynting-Robertson effect + Radiation Pressure
[
Rodmann, Wolf,
]
Spurzem, Henning, in prep.
Resonant structures can serve
as indicators of a planet in a
circumstellar disk
[1] Location
[2] Major orbital parameters
[3] Mass of the planet
(static)
equilibrium
density
distribution
Scattered Light Image
104 particles
107 particles
Relative brightness distribution of individual clumps in optical to near-infrared scattered
light images may sensitively depend on the disk inclination.
(Wilner et al. 2002)
(Holland et al. 1998, Wilner et al. 2002)
SOFIA, JWST
Debris disk around Vega
Dust reemission
Su et al. (2005):
• No clumpy structure
• Inner disk radius: 11”+/-2”
• Extrapolated 850μm flux
<< than observed
70μm
• Explanation:
Dust
grains
sizes
(Holland
et al. of
1998,different
Wilner et al. 2002)
are traced by Spitzer/SCUBA
Spitzer
Debris disk around Vega
24μm
Giant Planets in Debris Disks
Characteristic Asymmetric
Density Patterns
Rodmann & Wolf (2006)
Decreased Mid-Infrared
Spectral Energy Distribution
(but dust grain evolution makes detailed SED
analysis difficult)
Wolf & Hillenbrand
(2003, 2005)
[ aida28.mpia.de/~swolf/dds ]
Giant Planets in Debris Disks
Characteristic Asymmetric
Density Patterns
Rodmann & Wolf (2006)
Decreased Mid-Infrared
Spectral Energy Distribution
(but dust grain evolution makes detailed SED
analysis difficult)
Wolf & Hillenbrand
(2003, 2005)
[ aida28.mpia.de/~swolf/dds ]
Giant Planets in Debris Disks
Characteristic Asymmetric
Density Patterns
Rodmann & Wolf (2006)
Decreased Mid-Infrared
Spectral Energy Distribution
(but dust grain evolution makes detailed SED
analysis difficult)
Wolf & Hillenbrand
(2003, 2005)
[ aida28.mpia.de/~swolf/dds ]
Inner cavity in an optically thin disk
surrounding a solar-type star
Gaps
Fe content
Inner disk
radius
Grain
size
SED
T Tauri Disks
GM Aurigae, TW Hya
[Koerner et al. 1993, Rice et al 2003,
Calvet et al. 2002]
Debris Disks
β Pic (20AU), HR 4796A (3050AU), ε Eri (50AU), Vega
(80AU), Fomalhaut (125AU) +
„new“ Spitzer Debris Disks
[Dent et al. 2000, Greaves et al. 2000,
Wilner et al. 2002, Holland et al. 2003]
Wolf & Hillenbrand (2003)
The Young Solar System @ 50pc
Mdust = 10-10Msun
with
planets
without
planets
Moro-Martin, Wolf, & Malhotra (2004)
Some problems with SEDs...
Kim et al. 2005
Some problems with SEDs...
Many of the debris disks observed with the Spitzer ST,
show no or only very weak emission at wavelengths < 20…30 micron
(e.g. Kim et al. 2005)
=> No / weak constraints on the chemical composition of the dust
Debris disks: Optically thin
- azimuthal and vertical disk structure can not be traced
via SED observations / modelling;
- only constraints on radial structure can be derived: SED = f ( T(R) )
but even here ambiguities are difficult to resolve …
Imaging required
Moro-Martin, Wolf, & Malhotra (2005)
(Schultz, Heap, NASA 1998)
β Pictoris dust disk:
• Orientation : nearly edge-on
• Total mass :
few tens ... few lunar masses
Warp in
the β Pictoris Disk
Model includes a
Disk of Planetesimals
• Extending out to 120-150AU,
perturbed gravitationally by a
giant planet on an inclined orbit
• Source of a distribution of grains
produced through collisional
evolution
• Maximum of the dust surface
density distribution located
between 80AU and 100AU
(Zuckerman & Becklin 1993, Holland et al. 1998,
Dent et al. 2000, Pantin et al. 1997)
(Augereau et al. 2001, see also Mouillet et al. 1997)
Concluding Remarks
1. SED: (sub)mm slope
2. Shape of 10μm silicate feature
3. Scattered light polarization
4. Multi-wavelength imaging
5. Vertical Disk Structure
Concluding Remarks
Vortices
=> Local Density Enhancements
=> enhanced grain growth
(e.g., Wolf & Klahr 2003, Klahr & Bodenheimer 2006)
Concluding Remarks
1. Gaps
2. Global Spiral Structures
3. Planetary Accretion Region
4. Center-of-light-wobble
5. Inner holes
SIM
Concluding Remarks
1. Characteristic Asymmetric Patterns
2. Shape of the mid-infrared
Spectral Energy Distribution
3. Warps (β Pic)
Concluding Remarks
Theoretical investigations show that the planet-disk interaction causes structures
in circumstellar disks, which are usually much larger in size than the planet
itself and thus more easily detectable. The specific result of the planet-disk
interaction depends on the evolutionary stage of the disk.
Numerical simulations convincingly demonstrate that high-resolution imaging
performed with observational facilities which are already available or will
become available in the near future will allow to trace these signatures
of planets.
These observations will provide a deep insight into specific phases
of the formation and early evolution of planets in circumstellar disks.