Cumber01.ppt 30.5.2001

Thomas HenningMax-Planck-Institut für Astronomie, Heidelberg

Protoplanetary Accretion DisksFrom 10 arcsec to 10-3 arcsec

HST STIS – Grady et al. 2001 HD 100 546

NIR/Mid-IR thermal dust (VLTI: Midi, Amber)

Scattered Light in Optical and NIR (opt. thick)

mm / submm thermal dust emission (opt. thin)

Optically thick CO lines

thin lines

Domain sampledin current imagesat 150 pc

0

- 200

200

~ 500~ 100~ 50~ 1

Ver

tica

l sca

le n

ear

the

star

Approximate radius r (AU)

Ap

pro

xim

ate

H(r

) at

500

AU

(A

U)

Flaring?

Planetesimals?Acc. Rate ~10-8M⊙/yr

Accretion columns(broad emission lines: Hα, etc)

Accretion shock

Stellar magnetosphere

Accretion disk ~ Kuiper Belt

Passive reprocessing disk

Wind

Cumber03.ppt 30.05.2001

Adapted from A. Dutrey

Spatial Resolution

Region TW Hydrae Taurus / Chamaeleon Orion BN/KL Association OPH Distance 50 pc 150 pc 450 pc

Instrument (/Resol.) Linear Resolution AU

Normal Telescope (1m, 1) 50 150 450 VLA (6cm, 0.4) 20 60 180

3.6m/AO (2m/0.2) 10 30 90 HST (1m, 0.1) 5 15 45

3.6m (10m, 1) 50 150 450 ESO SEST (1mm, 23) 1000 3000 104

ESO VLT (10m, 0. 34) 15 50 150 ESO AO (2.2m, 0.08) 3 12 36

ESO VLTI (10m, 0.03) 1 4 12 JWST (1m, 0.03)

LBT (10m, 0.2) 10 30 90 LSA (1mm, 0.2)

Fundamental Questions

• How is angular momentum transported in disks (Self-gravity, turbulence – MRI or global baroclinic instability)?

• How do planets form in disks?

• Is the accretion process important for star formation (IMF)?

Klahr & Bodenheimer (2003)

Open Issues

• Geometrical structure (inner+outer edge, vertical structure, flaring, warps, gaps, ...)

• Temperature and density distribution

• Accretion rate – time variation

• Chemistry in disks and evidence for grain growth

• Transition from optically thick to optically thin disks

• Disk structure vs. nature of central star

How do we know that disks exist?

Inference

• Theory of SEDs• Infrared emission• Millimetre dust continuum emission• Polarization of light• Jets

”Proof ”

• HST images• Millimetre maps (interferometry)• Adaptive optics images• Images in the thermal infrared

Speckle and AO-assistedObservations from the ground(scattered light, extinction lanes)

IRN ChaAgeorges et al. 1996

HV Tau CStapelfeldt et al. 2003

HST (coronographic) images:STIS, NICMOS, WFPC(scattered light, extinction lanes)

Thermal infrared observations

Millimetre continuum and linedata (dust emission – opticallythin; gas emission – mostly optically thick)

HR 4796 A – Telesco et al. 2000

CB 26 - Launhardt & Sargent 2001

Geometrically thin disks (Adams et al. 1988)

• Temperatures correspond to unique radii Td (r) = 1000 K (r/1AU)-3/4

• Each frequency traces distinct temperatures

• S = cos B (Td (r) ) [1- exp (- ())] 2r dr/D2

() <<1 S ~ () Mdisk (Rayleigh-Jeans limit)

() >>1 S ~ 4/3 (Reprocessing or accretion)

SEDs from a geometrically thin simple disk almost never fit

observed SEDs Industry of more sophisticated models

Silicate Emission in T Tauri Disks

Natta, Meyer, & Beckwith, ApJ, 2000.

SEDs of T Tauri Stars:

A Consequence of Inner Holes?

Dullemond et al. 2001

The GM Aurigae DiscussionAnalysis of SED (Rice et al. 2003)

Inner hole created by a ~ 2 Mj planet orbiting at 2.5 AU in a disc with mass 0.047 Msun andradius 300 AU

But: SED contains limited spatial information (geometry / opacity problem) Boss & Yorke 1993, Steinacker & Henning 2003

Other mechanisms:• Disc wind caused by photoevaporation (Clarke et al. 2001)

• Higher temperature due to accretion shock front (d‘Alessio et al. 2003)

• Destruction of grains by non-thermal processes (Lenzini et al. 1995, Finocchi et al. 1997)

Structure in Disks

• Structure in disks older than 2 Myr is common.

• Seen in T Tauri and Herbig Ae stars.

• In some cases associated with dynamical clearing

DL Tau

DM TauHD 141569A,Mouillet et al. 2000

HR 4796A, Schneider et al. 2001

HD 100546

Where Are Envelopes Seen?

• Associated with single, isolated stars.• All objects with large-scale nebulosity have distinctive mid-IR

spectra.• While the optical depths appear to drop with age, these large-

scale nebulosities are seen over the entire PMS lifetime of intermediate-mass stars.

SU Aur HD 100546 CQ Tau

Properties of T Tauri Disks: What is Known?

• 50% of the objects have disks

• Mdisk << M* in case of T Tauri stars

(typically: Mdisk 10-2 Msun)

• Disk diameters: 50-200 AU• Disk lifetime: 106 yr

• Accretion rates: 10-9 ... 10-7 Msun yr-1

Disk Structure Inferred from IR

• Near-IT traces emission r < 0.1 AU Some evidence for inner holes in accretion disks

• Mid-IR spectro-photometry from KAO/ISO/ground: Indicates optically thin hot dust r < AU

• Far-IR observations of outer disk 1-5 AU Warm grains in disk atmosphere?

Factors Influencing Disk Evolution

• Stellar mass: Do high mass stars lose disks

quicker?

• Close companions: dynamical clearing of gaps (Jensen et al. 1995; 1997; Meyer et al. 1997b; Ghez et

al. 1997; Prato et al. 1999; White et al. 2001).

• Formation environment: cluster versus isolated star formation

Growth Processes in Disks

1 mm Dust grains 0.1 – 1 mm - Gas-dust interactions

- “Sticking” collisions in multi-particle systems

1-10 km Planetesimals ~ 10 km - Gravitational interaction (Decoupling from the gas)

- Agglomeration by pairwise collisions - Explosive growth of the largest planetesimals

in the accretion zone 103 km Protoplanets – dynamically isolated

- Accumulation of solid material - Accumulation of H2 und He by massive

protoplanets

Cumber12.ppt 5.6.2010

Grain Growth

Some evidence for grain growth from mm observations and polarization studies in the IR

Micron- to centimetre-sized grains and agglomerates stick at the typical relative velocities occurring in protoplanetary disks

Grains couple with f m/s gvth to the gas

Agglomerates produced by Brownian motion (and most likely by other velocity fields) have open structure: f R0.2

Crystalline silicates exist in protoplanetary disksCumber05.ppt 30.5.2001

Cumber01.ppt 30.5.2001

Aggregate Structures – Experimental Results

Evidence for grain growth

• Decrease in the NIR emission – TTS more than 3 million years old no longer have disks dominated by micron-sized grains (Dutkevich 1995)

• Flatter SEDs at millimetre wavelengths (Mannings and Emerson 1994, Koerner et al. 1995)

• Gray opacities in the dense core region around HL Tau from detailed RT modeling (Menshchikov & Henning 1998)

• Formation of gaps (Koerner et al. 1998: HR 4796)

• Geometrically thin disks (Alessio et al. 2001)

• Radiative transfer modeling of Herbig Ae/Be stars (Bouwman et al. 2000, Meeus et al. 2001)

• Wavelength-dependent disk size (Throop et al. 2001) ???

Cumber08.ppt 1.6.2001

Crystalline Silicates

Przygodda et al.(2003)

Dust Opacity: Effects of Size and Composition shown at R=100(Henning et al. 2000)

Images of edge-on disks at = 0.814m for dust mixtures

Cumber11.ppt 5.6.2001D’Alessio et al. (2001)

Time Scales For Grain EvolutionTime Scales For Grain EvolutionTime Scales For Grain EvolutionTime Scales For Grain Evolution

t 5 106 yr(from infrared excess emission)

(1) Dust grains have been thoroughly removed from circumstellar disks.

(2) Grains have been evolved into larger bodies (reduced effective radiating surface).

(3) (Replenishment of grains in disks around Vega-type stars (t 100Myr) by collisional shattering of lager bodies)

Cumber04.ppt 30.5.2001

The Transition between Thick & Thin:

• Primordial Disks: – opacity dominated by primordial grains.

• Debris Disks:– Opacity dominated by grains produced through

collisions of planetesimals.

• How can you tell the difference?– Absence of gas (Gas/Dust < 0.1) argues for short

dust lifetimes (blow-out/P-R drag).

– Dust processing through mineralogy?

Cumber16.ppt 12.6.2001

DUST SEDIMENTATION

Schräpler & Henning (2003)

Herbig Ae/Be Stars - Observations

Disk geometries proposedfor Herbig Ae/Be stars

Group Iwith FIR excess

Group IIno FIR excess

flaring disk self-shadowing disk

The special feature of these models isthe puffed-up hot inner rim of the disk

Dullemond, Dominik & Natta 2001Dominik, Dullemond, Waters & Walch 2003

Detecting Planets in Protoplanetary Disks

Radial density profile in themidplane (M = 1 Mj at 5.2 AU)

Normalized visibilities at = 10m,d = 140 pc(0° - face on, 60°)

Wolf et al. (2002), Steinacker & Henning (2003)

Conclusions

Brandner et al. (2000)

• Goal – Imaging of disks with infrared and millimetre interferometry (Evidence for disk structure and grain growth scarce)

• Fundamental physical processes not understood (Complicated interplay between microphysics and MHD)

This is the end