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Protoplanetary Disks: An Observer’s Perpsective

David J. Wilner (Harvard-Smithsonian CfA)

RAL 50th, November 13, 2008

Chunhua Qi

Meredith Hughes

Sean Andrews (Hubble Fellow)

Andrews et al. 2008Burrows et al. 1996

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Circumstellar Disks• integral part of star/planet

formation paradigm before disks spatially resolved– inevitable consequence of

gravity + ang. mom.

– Solar System fossil record

– preponderance of circumstantial evidence

• observational challenges

– bulk of disk mass is cold (and dark) H2, probed by minor constituents only

– Solar System scales small, difficult to image

Shu, Adams & Lizano, 1987 ARA&A

100 AU0.7” @ 140 pc

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Panchromatic Systems

Dullemond et al. 2007

x-ray uv optical mid/far-ir submm cmhot gas/accr. starlight warm… cool gas & dust

dust dominates the opacity, gas dominates the mass

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• optical shadows are beautiful but opaque mm emission

• Imm B(T)(1 - e-)d– 1 - e- where

dust emissivity

– Rayleigh-Jeans: B(T) T

• Lmm ∫ T Md

• typical Md 0.01 M

(wide range exists)

Disk Masses

Andrews & Williams 2007 (cf. Beckwith et al. 1990)

for > 300 systems in nearby Taurus and Oph clouds

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Disk Mass Distributions

“Minimum Mass Solar Nebula” Steady Irradiated Disk

~ r-1.5

Weidenschilling 1977 (also Hayashi 1981)

D’Alessio et al. 2001

~ r-1.0

csH (Shakura & Sunyaev 1973)

~ (dM/dt)/3(r1.5T)-1r-1

(r) ~ r -p

— Adams, Shu & Lada 1988

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flux limited sample: Oph (125 pc) and TWA (50 pc) regions

870 microns, 0.25” resolution, surface density structure to r < 20 AU

Submillimeter Array Survey

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SMA Survey (12 disks so far)

Oph TWA100 AU

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Surface Density Distributions• fit resolved submm data

and SED simultaneously– stellar properties

– dust properties (uniform)

– Dullemond RADMC code (temperature structure computed, not imposed)

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Surface Density Distributions

densities comparable to MMSN (extrapolation) + significant mass reservoir

good potential for planet formation (e.g. Inaba et al. 2003, Hubickyj et al. 2005)

r-1

Andrews et al., in prep

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• other two Oph disks… diminished emission inside r ~ 20-40 AU

growing sample of disks with large central holes

Evidence for Central Holes

J. Brown, Ph.D. thesis (see Pontoppidan et al. 2008)

Andrews et al., in prep

mechanism(s)?

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• CO: most abundant gas tracer of H2 (e.g.

Koerner et al. 1993, Mannings et al. 1997, Dutrey et al. 1997, Simon et al. 2000, …)

– low J lines collisionally excited, thermalized, optically thick (T r-0.5)

– confusion with ambient cloud is often a major problem

• many other (much weaker) species (e.g. Kastner et al. 1997, Dutrey et al. 1997, van Zadelhof et al. 2003, Thi et al.. 2004, …)

– rich chemistry: ion-molecule, deuteration, photo-, organics

– HCO+, DCO+, HCN, CN, DCN, CS, H2CO, CH3OH, …

Isella et al. 2007

Spectral Line EmissionSMA TW Hya CO 3-2

Hughes et al., in prep

(Qi et al. 2004, 2006)

SMA HD 163296 CO 3-2

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Velocity Fields

• Keplerian rotation – v r-0.5

• turbulence?– subsonic (if

present)

TW HyaSMA CO 3-2v = 44 m/s

Hughes et al., in prep

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Nebular Chemistry• D/H enhanced at low temps: H3

+ + HD H2D+ + H2 + E

• is pristine cometary material: “interstellar” or “nebular”?

• TW Hya: radial distributions of DCO+ and HCO+

– D/H ratio from 0.01 to 0.1 from r<30 to 90 AU

– in situ fractionation is important

Qi et al. 2008HCO+ 3-2 DCO+ 3-2

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Outer Edge Complexity

• power law models do not match observed extent of dust and CO emission – e.g. HD 163296: 200 AU (dust)

vs. 600 AU (CO)

– not limited sensitivity

– outer disk dust:gas ratio? dust opacity?

• accretion disk structure: exponential outer edge– reconciles dust and gas sizes

with same model

SMA 1.3/0.87 mmCO J=3-2

Hughes et al. 2008

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Disk Magnetic Fields• aligned dust grains

linear polarization– models: ~2% pol.

fraction 870 m (Cho & Lazarian 2007)

– tentative JCMT detections: toroidal field (Tamura et al. 1999)

• SMA polarimetry of HD 163296 – < 5x below model

– magnetic field geometry? grain alignment?

Hughes et al. in prep

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Concluding Remarks• observed disk properties are “protoplanetary”

– dust (Spectral Energy Distributions)

– gas (accretion, flaring, mm lines)

– sizes 10’s - 100’s AU (dust, mm lines)

– masses ~ 0.01 M (mm dust)

r -1 (mm dust)

– holes cleared by planets? (mm dust)

– kinematics Keplerian (mm lines)

• ALMA on the horizon: full operation 2013?– 10-100x sensitivity, resolution, image quality– global partnership to fund >$1B construction

– disks are a Key Science Goal

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END

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Evidence for Central Holes• GM Aur disk: diminished opacity for R < 24 AU

C. EspaillatCalvet et al. 2005

Hughes et al., in prep

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Transition Disk Models

• dynamical clearing by planet– planet interacts tidally with disk,

transfers angular momentum, opens gap, viscosity opposes (Papaloizou & Lin 1984, …)

• photoevaporation – accretion rate drops below mass

loss rate, open gap: “uv switch” (Clarke et al. 2001,…)

• demographics favor planets– large masses

– modest accretion rates

Najita et al. 2007

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• infrared excess

• 50% (90%) gone by 3 (5) Myr

• also gas accretion timescale

• 1-2 Myr T-Tauri stars

• Lmm ∫B(T)(1 - e-)d T

• <Md> 0.01 M

Disk Mass and Disk Dispersal

Andrews & Williams 2007 (cf. Beckwith et al. 1990)

Hernandez et al. 2007(cf. Haish et al. 2001)

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Disk Evolution: Multiple Paths?

B. Merin, Spitzer c2d team

primordialdisk

“cold” disk

“anemic” disk

debris disk

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At the Limits of ALMA• hypothetical planet in TW Hya disk

model density distribution

simulated ALMA 900 GHz imageWolf & D’Angelo 2005

5 AU