Prospects for the Detection of Protoplanets€¦ · Alternativ: Gravitational Instability Giant...

Prospects for the Detection of Protoplanets[Review]

discs06 – Cambridge, UK [July 20, 2006]

Sebastian WolfEmmy Noether Research Group

“Evolution of Circumstellar Dust Disks to Planetary Systems”Max Planck Institute for Astronomy

• Gravitational Interaction: Oligarchic Growth

• Agglomeration; Fragmentation

• Brownian Motion, Sedimentation, Drift• Inelastic Collision => Coagulation

Planet Formation in a Nutshell Theory

(Waelkens 2001)

Star Formation Process Circumstellar Disks Planets

(sub)µm particles

cm/dm grains

Planetesimales

Planets (cores)

Alternativ: Gravitational Instability Giant Planet

• Gas Accretion

HK Tau

IRAS 04302+2247

• SED: (sub)mm slope

• Shape of ~10μm silicate feature

• Scattered light polarization(e.g., spectro-polarimetry)

• Multi-wavelength imaging

+ Radiative Transfer Modelling

how to identify

Grain Growth?

HK Tau

IRAS 04302+2247

The “Butterfly Star” in Taurus

IRAS 04302+2247

Wolf, Padgett, & Stapelfeldt (2003)

HK Tau

IRAS 04302+2247

The “Butterfly Star” in Taurus

IRAS 04302+2247 Wol

f, Pa

dget

t, &

Sta

pelfe

ldt (

2003

)

600 A

U ~

4.3”

submm-sized grains in the disk midplane,

instellar-like grain size in the circumstellar envelope

Size Scales

Solar System

Angular diameter of the orbit of solar system planets in a distance of the Taurus star-forming region (140pc)

Neptune - 429 mas Jupiter - 74 masEarth - 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

IR – mm

Scattering

Thermal Reemission

Young disks Extinction (Inclination-dependent)

Additional Problems (Dust...)

Dust parameters, T(r,θ,φ), ρ(r,θ,φ)

(Bate et al. 2003)Disk surface densities for planets with masses 1, 0.1, and 0.01MJ orbiting a 1Msun star

Response of a gaseous, viscous protoplanetary disk to an embedded planet

[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)

1 MJ

0.3 MJ

0.03 MJ

0.01 MJ

[ G. Bryden ]

Is this what we have to

look for?

Jupiter in a 0.05 Msun disk

arounda solar-mass staras seen with ALMA

(Wolf et al. 2002)

d=140pc

Baseline: 10km

λ=700μm, tint=4h

[Varniere et al. 2006]

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)

no gap[ no planet ]

gap[ 2MJ planet at 1 AU ]

inclination = 5°

inclination = 70°

Log( Disk surface brightness)

Azimuthally averaged optical surface brightness profiles for a disk with / without an embedded planet.

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 ]

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)

Richling (in prep.): Observability of gaps depending on wavelength + viewing angle (based on irradiated α-disk models)

2MJ planet at 1 AU

Gapsin 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)

Small-scale spirals encircling the planet (detached from the global spiral)

=

Feature of a circumplanetary disk

Is this what we have to look for?

Density distribution in the midplaneof the circumstellar disk with an embedded massive planet.

Can we map young giant planets?

Close-up view: Planetary region

ProcedureDensity Structure

(2D Hydrosimulation)

Stellar heating (3D Radiative transfer)

Planetary heating (3D Radiative transfer)

Prediction of Observations

Wolf & D’Angelo (2005)



Maximum baseline: 10km, 900GHz, tint=8h

Mplanet / Mstar = 1MJup / 0.5 Msun

Orbital radius: 5 AU

Disk mass as in the circumstellar disk as around the Butterfly Star in Taurus

50 pc

100 pc 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



50 pc

100 pc

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.

Gapsin young disks

-two-fluid simulations

Strong spiral shocks near the planet are able to decouple the larger particles (>0.1mm)

from the gas

=>

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)

PaardeKooper & Mellema (2004)

Imaging in the Mid-infrared (~10micron)

Hot Accretion Region around the Planet

i=0deg i=60deg

10μm surface brightness profile of a T Tauri disk with an embedded planet ( inner

40AUx40AU, distance: 140pc)

[Wolf & Klahr, in prep.]

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

30 pc10 pc 70 pc

T-OWLThermal Infrared Camera for OWL

Wolf, Klahr, Egner, et al. 2005 in Lenzen et al. 2005

5 AU

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-infrared3 new mid-IR observing windows for interferometry (L,M,Q)

• Improved Spectroscopic Capabilities

MATISSEMulti AperTure Mid-Infrared SpectroScopic Experiment

High-Resolution Multi-Band Image Reconstruction+ Spectroscopy in the Mid-IR

MATISSE

Precursor of Darwin in terms of image reconstruction;Experience (MIDI + AMBER)

MATISSE

10μm image of a circumstellar disk with an inner hole, radius 4AU (inclination: 60deg; distance 140pc; inner 60AU x 60AU)

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)

increasing planetary mass

Rice et al. (2003)

Azimuthally averaged mid-plane density profiles for substellar objects (planets).

The SED of GM Aur computed using azimuthally averaged density profiles.

Constraints on a planetary origin for the gap in the protoplanetary disc of GM Aurigae

• 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.

Jupiter @ 5AU

Solar-type central star

2.2 micron (scattered stellar light)

Imaging in the Near-infrared

AB Aurigae - Spiral arm structure (Herbig Ae star; H band; Fukagawa, 2004)

Inner disk (< a few AU)

Young disksWhich disks to study?

Preparatory studies,

concentrating on face-on disks

Useful techniques:

Coronography;

Differential polarimetric

imaging;

high-resolution mm maps

Clearly identified disks, well studied, but …potentially ”planet-building sites” well hidden…

Etc. ...

Very distant …

AB Aurigae HD 100546

(Grady 2001 / 2003)

Influence on the Net - SED


Inner Disk

inner ~12 AU



Planet

inner ~12 AU



Planetary Environment

inner ~12 AU



Inner Disk

+

Planet

+

Planetary Environment

No significant effect on the

Net SED

inner ~12 AU


Planetary Contribution (direct or scattered radiation, dust reemission)

Disk reemission (inner 12 AU)

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*).

< 0.4%(depending on the particular model)

see also Varniere et al. (2006)

High-Spatial Resolution

Spectroscopy

GSMT Science Case Study

[ www.aura-nio.noao.edu ]

Spectroscopic verification of gaps through their dynamics

R ~ 105, λ ~ 5-30μm

(Winters et al. 2003; see also Nelson & Papaloizou 2003)

GapsGapsin young disksin young disks

--MMHD HD

simulationssimulations

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

1. Planet’s Gravitational Pull

2. Disk’s Gravitational Pull

3. Disk’s Photospheric Signal(center-of-light wobble)

(G. Bryden, priv. comm.)

Sources of Astrometric Wobble

(G. Bryden, priv. comm.)

Center-of-Light-Wobble

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 observationsprobe 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 ( 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).

Young disks / Debris disksPlanet Disk interaction

Young circumstellar disks around T Tauri /

HAe/Be stars

Debris disks

optically thick

Gas dynamics

Density structure dominated by

Radiation Pressure

Poynting-Robertson effect

Gravitation +

optically thin

Scattered light images (optical)

BD+31643

AUMic

betaPic

HK Tau

IRAS 04302+2247

Characteristic Debris Characteristic Debris Disk Density PatternsDisk Density Patterns

Simulated surface density of circumstellar dust captured into particular mean motion resonances

(Ozernoy et al. 2000)

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 off-

center cavities, and

[2] A central cavity void of dust.

107 particles

(static) equilibrium

density distribution

Resonant structures can serve as indicators of a planet in a

circumstellar disk

[1] Location

[2] Major orbital parameters

[3] Mass of the planet

Rodmann, Wolf,

Spurzem, Henning, in prep.[ ]dynamical simulation

• ~ 104 massless particles

• gravitational intercation with planet + star

• Poynting-Robertson effect + Radiation Pressure

Scattered Light Image104 particles

107 particles104 particles

(static) equilibrium

density distribution

Resonant structures can serve as indicators of a planet in a

circumstellar disk

[1] Location

[2] Major orbital parameters

[3] Mass of the planet

Scattered Light Image

Relative brightness distribution of individual clumps in optical to near-infrared scattered light images may sensitively depend on the disk inclination.

Dust reemission(Wilner et al. 2002)

(Holland et al. 1998, Wilner et al. 2002)

Debris disk around Vega


SOFIA, JWST

(Holland et al. 1998, Wilner et al. 2002)



Spitzer

24μm

70μm

Su et al. (2005):

• No clumpy structure

• Inner disk radius: 11”+/-2”

• Extrapolated 850μm flux

Giant Planets in Debris Disks

Characteristic Asymmetric Density Patterns

Decreased Mid-Infrared Spectral Energy Distribution(but dust grain evolution makes detailed SED

analysis difficult)

Wolf & Hillenbrand (2003, 2005)

Rodmann & Wolf (2006)

[ aida28.mpia.de/~swolf/dds ]

Giant Planets in Debris Disks

Characteristic Asymmetric Density Patterns

Decreased Mid-Infrared Spectral Energy Distribution(but dust grain evolution makes detailed SED

analysis difficult)

Wolf & Hillenbrand (2003, 2005)

[ aida28.mpia.de/~swolf/dds ]

Rodmann & Wolf (2006)

Gaps SEDGaps SEDInner cavity in an optically thin disk

surrounding a solar-type star

Wolf & Hillenbrand (2003)

Grain size

Fe content

Inner disk radius T Tauri Disks

GM Aurigae, TW Hya[Koerner et al. 1993, Rice et al 2003,

Calvet et al. 2002]

Debris Disksβ Pic (20AU), HR 4796A (30-

50AU), 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]

The Young Solar System @ 50pcThe Young Solar System @ 50pc

Moro-Martin, Wolf, & Malhotra (2004)

with planets

without planets

Mdust = 10-10Msun

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, N

ASA

1998)

Warp in the β Pictoris Disk

β Pictoris dust disk:• Orientation : nearly edge-on

• Total mass : few tens ... few lunar masses

• 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)

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

(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 structuresin circumstellar disks, which are usually much larger in size than the planetitself 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 imagingperformed 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 phasesof the formation and early evolution of planets in circumstellar disks.

Prospects for the Detection of Protoplanets�[Review]Size Scales Mid-infrared interferometric spectroscopy - Dust processing in the innermost regions Mid-infrared interferometric spectroscopy - Dust processing in the innermost regions Finding Planets – In Disks?!Is this what we have to look for?MATISSE� Multi AperTure Mid-Infrared SpectroScopic ExperimentMATISSEInner disk �(< a few AU)

Prospects for the Detection of Protoplanets€¦ · Alternativ: Gravitational Instability Giant...

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