Planetary Signatures in Circumstellar Disks

Sebastian Wolf University of Kiel, Germany

WII09, Goutelas (France), 26.05.-29.05.2009 Overview

Introduction

• Large-scale structures in circumstellar disks @ various wavelengths: Exemplary case studies

• Small-scale structures in circumstellar disks @ various wavelengths: Future prospects on disk-planet interaction observations

• Planets in debris disks

Focus: Dust Introduction:

Stars – Disks – Planets Stars – Disks - Planets Planet Formation in a Nutshell

Star Formation Process Circumstellar Disks Planets

Core Accretion – Gas Capture (sub)µm 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 grain growth?

λFλ • Spectral Energy Distribution (SED) −β (sub)mm slope: Fν ~ κν ~ λ • Dust emission/absorption features 1μm 100μm λ • Scattered light polarization • Multi-wavelength imaging

+ Radiative Transfer Modelling

O/ ~ 10μm credit: NASA Wolf et al. 1997-2000 Wolf 2003 Monte Carlo Radiative Transfer

• Monte Carlo method: – Very powerful (e.g., wide range of optical depths) + flexible (model) – Direct Implementation of Physical Processes (e.g., Photon transport, Scattering, Absorption, Reemission)

• 3D continuum radiative transfer code MC3D – Well-tested, Former Applications: Globules, Disks, Clumpy circumstellar shells and AGN tori, ... – Models: • (almost) Arbitrary model geometry / density distribution • Arbitrary heating sources (e.g., Stars, Accretion disks) • Arbitrary optical properties of the absorbing/scattering medium – Output: • Self-consistent temperature distribution • Spectral energy distribution • Wavelength-dependent Images, Polarization Maps www1.astrophysik.uni-kiel.de / asd

http://www1.astrophysik.uni-kiel.de/asd ASTROPHYSICS SOFTWARE DATABASE

Foster the communication between developers and users of astrophysical software

Provide an overview about existing software solutions in the community

Cross-linked with the NASA ADS Large-scale structures of circumstellar disks @ various wavelengths

(~10 – a few 100 AU, i.e., > 0.1“) Exemplary studies

Example #1: Butterfly star in Taurus Example #1 The Butterfly Star in Taurus

1.10 μm

1.60 μm

HST/NICMOS 1.87 μm

2.05 μm

• Wavelength-dependence of the dust lane width • Relative change of the brightness distribution from 1.1μm-2.05μm 6.4” x 6.4” • Slight symmetry of the brightest spots [Wolf et al. 2003] [Padgett et al. 1999] Example #1 The Butterfly Star in Taurus

OVRO

• Disk density profile

• Envelope structure Resulting from mass infall under consideration of envelope rotation (Ulrich 1976)

• Heating Sources Star (Blackbody), Accretion

• Dust Properties Grain size distribution:

Chemical Composition: Astr. Silicate, Graphite [ Wolf et al. 2003 ] Example #1 The Butterfly Star in Taurus

Disk outer radius: 300 AU Radial/Vertical density profile: α=2.37, β=1.29 Disk scale height: h(100AU) = 15AU

Disk Grain size distribution: aGrain = (0.005 – 100) μm

-2 Disk Mass: 7 x 10 Msun

-4 Envelope Mass: 4.8...6.1 x 10 Msun

Confirmation of different dust evolution scenarios in the circumstellar shell and disk: 1. Interstellar dust (< 1μm) in the shell 2. Dust grains with radii up to ~100μm in the circumstellar disk! J band polarization map (Lucas & Roche 1997 – IRCAM-3/UKIRT) Linear Polarization:up to 80% Scattering dominated by interstellar-type grains Example #1 The Butterfly Star in Taurus

1360μm

894μm

constraints on radial + vertical disk structure [Wolf et al. 2008] in the potential planet-forming region (r~80-120AU) Exemplary studies

Example #2: HH30 Example #2 HH30

Observation • IRAM interferometer, 1.3mm, ”beam size ׽0.4

Results • Disk of HH30 is truncated at an inner radius 37 ± 4 AU.

Interpretation • Tidally truncated disk surrounding a binary system (two stars on a low eccentricity, 15 AU semi-major axis orbit) • Additional support for this interpretation: Jet wiggling due to orbital motion • The dust opacity index, β ≈ 0.4, indicates the presence of cm size grains (assuming that the disk is optically thin at 1.3mm)

“… In this domain, ALMA will likely change our observational vision of these objects.“

[Guilloteau et al. 2008] Example #2 HH30

Observation • IRAM interferometer, 1.3mm, ”beam size ׽0.4

Results • Disk of HH30 is truncated at an inner radius 37 ± 4 AU.

Interpretation • Tidally truncated disk surrounding a binary system (two stars on a low eccentricity, 15 AU semi-major axis orbit) • Additional support for this interpretation: Jet wiggling due to orbital motion • The dust opacity index, β ≈ 0.4, indicates the presence of cm-size grains (assuming that the disk is optically thin at 1.3mm)

“… In this domain, ALMA will likely change our observational vision of these objects.“

[Guilloteau et al. 2008] Exemplary studies

Example #3: CB 26 (Taurus) Example #3 Disk in the Bok Globule CB26

Observations considered • HST NICMOS NIR imaging • Submm single-dish: SCUBA/JCMT, IRAM 30m • Interferometric mm cont. maps: SMA (1.1mm), OVRO (1.3/2.7mm) • SED, including IRAS, ISO, Spitzer

[Sauter et al., subm.] Example #3 Disk in the Bok Globule CB26

Main Conclusions

• Dust – ISM dust grains in the envelope and „upper“ disk layers – Dust grains in the disk midplane slightly larger than in the ISM (2.5μm)

• Disk – Inner disk radius: ~ 45 +/- 5 AU

– Mass: 0.3MSun

– h(100AU) = 10 AU, α = 2.2, β = 1.4, rout = 200 AU Small-scale structures of circumstellar disks @ various wavelengths

(<10 AU, i.e., <0.1“) Size Scales Size scales Solar System

IRAS 04302+2247 Angular diameter of the orbits of selected Solar System „Butterfly Star“ planets as seen from the distance of the nearby star- forming region in Taurus (140pc) : Neptune - 0.43” Jupiter - 0.074” Earth - 0.014”

What is possible? –TODAY AMBER / VLTI ~ a few mas [near-IR] MIDI / VLTI ~ 10 – 20 mas [N band: ~8-13μm] SMA ~ 0.3” (goal: 0.1”) [~submm] Size Scales Size scales Solar System

What is possible? – WITHIN THE NEXT DECADE (examples)

VSI / VLTI ~ a few mas [near-IR] 4-6 telescopes; image reconstruction MATISSE / VLTI ~ 10 – 20 mas [L/M/N bands: ~3-13μm] ALMA ~ 20 mas [~submm] Spectro-Interferometry in the mid-infrared

Schegerer, Wolf, et al., A&A 478, 779, 2008, „The T Tauri star RY Tauri as a case study of the inner regions of circumstellar dust disks “

Schegerer, Wolf, et al. 2009, A&A, in press „Tracing the potential planet-forming region around seven pre-main sequence stars“

Mid-Infrared Interferometric Instrument (MIDI)

Spatial resolution: λ/B ≥ 1AU @ 140pc with B ≤ 130m

Spectrally resolved (R=30) data in N band: • Silicate feature + (relative) radial distribution • Inner disk region ≤ 40 AU

General results (1) SED (global appearance of the disk) + spectrally resolved visibilities can be fitted simultaneously (2) Best-fit achieved in most cases with an active accretion disk and/or envelope (3) Decompositional analysis of the 10μm feature confirms effect of Silicate Annealing in the inner disk (~ few AU) Inner regions of circumstellar disks

Squares: Inner radius of gas disks (from vibrational transitions

of CO @ 4,6μm; TGas > 1000K)

Underlying assumption: Gas rotates with Keplerian velocity => Line width => Inner disk radius

Circles: Inner radius of dust disk (Interferometry: filled circles; SEDs: open circles)

[ Najita et al. 2007 ]

Conclusions • Gas inside the sublimation radius of the dust • Near co-rotation radius ( angular velocity of the disk = angular velocity of the star) => Indicates coupling between stellar magnetic field and disk Vortices – Precursors of Protoplanets?

ρ(r,φ,z) Ι(r,φ)

0°

Klahr & Bodenheimer (2002)

Global baroclinic instability

30°

Turbulence Reemission Images

(900GHz / 333μm) 10 AU Long-lived high-pressure overdense anticyclones 60° [ Wolf & Klahr 2002 ] Vortices – Precursors of Protoplanets?

Simulation: ALMA Baseline: 13km, 64 antennas Disk inclination 900GHz, Integration time 2hrs

Disk survey possible

50mas 50mas 50mas [ Wolf & Klahr 2002 ] Finding Protoplanets - In Disks?

UV – (N)IR Scattering

Additional Problems IR – mm Thermal Reemission (Dust!) Young disks Extinction (inclination-dependent)

= f ( dust properties, ρ(r,θ,φ), T(r,θ,φ) )

Solution: High-resolution Imaging Disk-Planet Interaction

1MJ 1Msun star

0.01 MJ

0.03 MJ

0.1MJ

0.3 MJ

1 MJ

0.01MJ

(Bate et al. 2003) ALMA: Gaps

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 ] Planetary Accretion Region

[ D’Angelo et al. 2002 ] [ Wolf & D’Angelo 2005 ]

Density Structure

Stellar heating

Planetary heating Procedure Prediction of Observation Close-up view: Planetary Region

[ Wolf & D’Angelo 2005 ]

Mplanet / Mstar = 1MJup / 0.5 Msun

Orbital radius: 5 AU Disk mass as in the circumstellar disk 50 pc as around the Butterfly Star in Taurus

Maximum baseline: 10km,

900GHz, tint=8h

Random pointing error during the observation: (max. 0.6”) ; Amplitude error, “Anomalous” refraction; Continuous observations centered on the meridian transit; 100 pc Zenith (opacity: 0.15); 30o phase noise; Bandwidth: 8 GHz Close-up view: Planetary Region

[ Wolf & D’Angelo 2005 ]

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. Larger distances: Contrast between planetary region and adjacent disk in all of the 50 pc considered planet / star / disk configurations will be too low to be detectable.

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.

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. 100 pc Influence on Net SED?

Planetary radiation significantly Inner Disk affects the dust reemission SED only in the near to mid-infrared wavelength range. Planetary Environment This spectral region is influenced also by the warm upper layers of the disk, the inner disk structure, Planet and the planetary contribution.

The presence of a planet + its basic characteristics (temperature, luminosity) cannot be derived from Planetary Contribution / Disk reemission (within the inner 12 AU ~ 0.1” in Taurus) < 0.4% the SED of the disk alone. (depending on the particular model)

[ Wolf & D’Angelo 2005 ] Shocks & MRI

Gas Dust 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.

(PaardeKooper & Mellema 2004)

MHD simulations - Magnetorotational instability • gaps are shallower and asymmetrically wider • rate of gap formation is slowed

Observations of gaps will allow to constrain the physical

Log Density in MHD simulations after 100 planet orbits for planets conditions in circumstellar disks with relative masses of q=1x10-3 and 5x10-3 (Winters et al. 2003) Complementary Observations: Mid-IR

Hot Accretion Region around the Planet

inclination: 0° inclination: 60°

10μm surface brightness profile of a T Tauri disk with an embedded planet (inner 40AUx40AU, distance: 140pc)

[ Wolf & Klahr, in prep. ] T-OWL

Planet Planet Planet

5 AU

10 pc 30 pc 70 pc [ Wolf, Klahr, Egner, et al. 2005 in Lenzen et al. 2005 ] Egner, Klahr, [ Wolf, High Resolution!

Requirement Multi-AperTure Mid-Infrared SpectroScopic Experiment MATISSE

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

2nd Generation VLTI Instrument

Specifications: • L, M, N band: ~ 2.7 – 13 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 2 new mid-IR observing windows for interferometry (L,M) • Improved Spectroscopic Capabilities

PI: B. Lopez (OCA Nice), Proj.Scient.: S. Wolf (CAU Kiel) Multi-AperTure Mid-Infrared SpectroScopic Experiment MATISSE

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

Successor of MIDI: Imaging capability in the entire mid-IR accessible from the ground

Successor of AMBER: Extension down to 2.7μm + General use of closure phases

Complement to ALMA + TMT/ELT

Ground Precursor of DARWIN Wavelength range 6-18μm Disk clearing?

Sublimation radius ~ 0.1-1AU (TTauri HAe/Be stars) but: Observations: Significant dust depletion >> Sublimation Radii TW Hydrae : ~ 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: 60°; distance 140pc; [ Wolf et al. 2005, 2006 ] inner 60AU x 60AU) MATISSE – Planets

Hot Accretion Region around the Planet

inclination: 0°

[ Wolf et al. 2005-2007 ] Scattered light images (I)

no gap gap λ = 1.14μm

[ no planet ] [ 2MJ planet at 1 AU ] Gap width (FWHM): ~ 1 AU. [7 AU × 7 AU]

based on 2D density distributions resulting from inclination = 5° hydrodynamics simulations vertical structure is

Log( Disk surface brightness) Log( Disk assumed to be Gaussian with a scale height that varies as a power law with radius (i.e., a flared disk)

inclination = 70° [Varniere et al. 2006] MATISSE – Planets

Hot Accretion Region around the Planet

inclination: 0°

[ Wolf et al. 2005-2007 ] Scattered light images (II): Surface Structure

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

K band scattered light image (Jupiter/Sun + Disk) [ Wolf & Klahr, in prep. ] Shadow – Astrometry

K band, scattered light

5 AU Space Interferometry Mission (SIM)

Wavelength range 0.4-0.9μm

[ Wolf & Klahr, in prep.] Baseline: 10m Narrow Angle Field: 1° Narrow Angle Astrometry 1μas mission accuracy Strategy Center of Light Wobble Conditions for the occurrence of a significantly large / strong shadow still have to be investigated [ G. Bryden, priv. comm.] 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.] High spatial resolution spectroscopy

Spectroscopic verification of gaps through their dynamics R ~ 105, λ ~ 5-30μm

GSMT Science Case Study Giant Segmented Mirror Telescope [ www.aura-nio.noao.edu ] Planets in Debris disks Disk Evolution

Time

(Waelkens 2001) (Lada 1987) Disk Lifetime: Inner Disk Region

Fraction of inner disks traced by near-IR excess dimishes to ~0 over a few Myr

(Haisch et al. 2001) Disk evolution: Mass

Protoplanetary disks Transitional Disks

Debris Disks

Step after ~10 Mio yr

Linear decrease after ~400 Mio yr

59 Disk Lifetime: Entire Disk

FEPS Upper Limits (groups of stars selected by age) Detections TW Hya

SEST, CSO, OVRO, IRAM: trace entire disk

165 solar-type stars (from FEPS legacy program):

0.5 – 2 Msun; 3 Myr – 3 Gyr ε Eri

- 9 new detections: ~10 - 200 Myr - 1 resolved mm source [ Carpenter, et al., 2005 ] [ Roccattagliata, et al., 2009 ] … but might still outshine embedded planets

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 •> 1μm: 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). Darwin Planet-Disk Interaction

betaPic

Circumstellar Disks Debris Disks around T Tauri and IRAS 04302+2247 HAe/Be stars

AUMic

optically thick; optically thin; gas-poor MGas/MDust ~100

Density structure dominated by Gravitation + HK Tau

BD+31643 Radiation pressure Gas dynamics Poynting-Robertson effect Stellar Wind Drag Structures in Debris Disks

[ Moro-Martin et al. ] Structures in Debris Disks

Figure caption:

Spatially resolved images of nearby debris disks showing a wide diversity of debris disk structure. From left to right the images correspond to:

(1st row) β-Pic (0.2–1 μm; Heap et al., 2000), AU-Mic (1.63 μm; Liu, 2004), TW Hydra (0.2–1 μm; Roberge, Weinberger and Malumuth, 2005);

(2nd row) HD 141569 (0.46–0.72 μm; Clampin et al., 2003);

(3rd row) Fomalhaut (0.69–0.97 μm; Kalas et al., 2005) and eps-Eri (850 μm; Greaves et al., 2005);

(4th row) HR4796 (18.2 μm; Wyatt et al., 1999), HD 32297 (1.1 μm; Schneider, Silverstone and Hines, 2005), Fomalhaut (24 and 70 μm; Stapelfeldt et al., 2004);

(5th row) Vega (850 μm; Holland et al., 1998), eps-Eri (850 μm; Greaves et al., 1998), Fomalhaut (450 μm; Holland et al., 2003), β-Pic (12.3 μm; Telesco et al., 2005), AUMic (0.46–0.72 μm; Krist et al., 2005).

[Moro-Martin 2008] Warp in the β Pic 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 (Schultz, Heap, NASA 1998)

• 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)

[ Augereau et al. 2001, see also Mouillet et al. 1997 ] Giant Planets in Debris Disks

Planet Resonances and gravitational scattering

Asymmetric resonant dust belt with one or more clumps, intermittent with one or a few off-center cavities + Central cavity void of dust.

Scattered Light Image [ Rodmann & Wolf ]

• Resonance Structures: Indicators of Planets [1] Location [2] Major orbital parameters [3] Mass of the planet

• Decreased Mid-Infrared SED [ Wolf & Hillenbrand 2003, 2005 ] www1.astrophysik.uni-kiel.de / dds The young Solar System

40μm 1μm -10 Mdust = 10 Msun

with planets

without planets

(distance: 50 pc, dust mass: 10-10 M ) sun [ Moro-Martin, Wolf, & Malhotra 2004 ] Imaging required!

First guess Planets of different mass at similar orbit

Solution Planets of same mass at different orbits

Important: Influence of dust composition

[ Moro-Martin, Wolf, & Malhotra 2005 ] Some Problems with SEDs

Spitzer ST

[ 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…30μm (e.g. Kim et al. 2005) No / weak constraints on the chemical composition of the dust

Debris disks: Difficult to observe

• Low Surface Brightness • Optically thin: Only constraints on radial structure can be derived: SED = f ( T(R) ) but even here degeneracies are difficult to resolve (e.g., planet mass, orbit, grain size) • Azimuthal (and vertical) disk structure can not be traced via SED observations / modelling Imaging is required! Debris Disks around Vega

24μm Spitzer ST

70μm

(Su et al. 2005)

• No clumpy structure • Inner disk radius: 11”+/-2” • Extrapolated 850μm flux << observed • Explanation: Dust reemission SOFIA, JWST Grains of different sizes

(Holland et al. 1998, Wilner et al. 2002) traced by Spitzer/SCUBA Concluding remarks

1. SED: (sub)mm slope 2. Shape of 10μm silicate feature 3. Scattered light polarization 4. Multi-wavelength imaging (Example: Butterfly Star) Concluding remarks

1. Imaging of the planet-forming Region (disk structure, e.g., Vortices) 2. Spectro-Interferometry Concluding remarks

1. Gaps 2. Global Spiral Structures 3. Planetary Accretion Region 4. Inner holes 5. Shadow / Center-of-light-wobble

SIM Concluding remarks

1. Characteristic Large-Scale Asymmetric Patterns

2. Shape of the mid-infrared (Schultz, Heap,NASA1998) SED 3. Warps (β Pic) Concluding remarks

Planet-disk interaction: Signatures in circumstellar disks • Usually much larger in size than the planet more easily detectable • Specific structure depends on the evolutionary stage of the disk 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.

Insight into specific phases of the formation and early evolution of planets in circumstellar disks.