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Grain Growth in Protoplanetary Disks:

the (Sub)Millimeter

Sep 11, 2006 From Dust to Planetesimals, Ringberg

David J. WilnerHarvard-Smithsonian Center for Astrophysics

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Relevance of (Sub)Millimeter

• “vibrational” dust emission is dominant mechanism (thermal fluctuations in charge distribution)

• longest observable ’s for dust: 0.35 to 35 mm

• sensitive to cold dust, T<10’s of K

• low opacity, sample emission at all disk depths dependence of opacity diagnostic of dust properties

(e.g. growth to millimeter size)

• no contrast issue with stellar photosphere

• major new facilities under construction: ALMA, eVLA

PPV: Natta, Testi, Calvet, Henning, Waters & Wilner, astro-ph/0602041

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ISM Protoplanetary Disks

0.85 mm

Johnstone & Bally 1999

Williams, Andrews, Wilner 2005

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• T Tauri, Herbig Ae disks (d≤150 pc, 1-10 Myr)– integrated flux vs. (single dish bolometer)

• observe power law form, F ~ -, 2 < < 3

– spatially resolved brightness (interferometer)

HD169142Dent et al. 2006

stardust

F~-2.5

(Sub)Millimeter Observables

SMA Raman et al. 2006

300 AU

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• mass opacity ( > 0.1 mm) power law form

• normalization, power law index , depend on dust properties:– composition– size distribution– geometry– …

(see Draine 2006)

Basics of “”

Adams et al. 1988, following Draine & Lee 1984

~-2

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• flux density emitted by an element dA

• if <<1 and h<<kT, then

and simply related to

F ~-(2+)

From to

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Beckwith & Sargent (1991)

Disk Dust appears Different

• early (sub)mm obs: disk <>~1 vs. ISM ~1.7 (e.g Weintraub et al. 1989, Adams et al. 1990, Beckwith et al.

1990, Beckwith & Sargent 1991, Mannings & Emerson 1994)

d=(-2)(1+)

0 1 2

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~1 Interpretations

1. changes in dust properties: – grain growth

small, a << /2 =2

large, a >> /2 =0 mm size, ~1

~ -1 due to dust composition particle geometry

2. optically thick emission: – F ~ -2 (in part) > ( - 2)

Pollack et al. 1994 mixture, compact, segregated spheres, n(a) ~ a-q, q=3.5

Calvet & D’Alessio 2001

amax=1 mm

amax=10 cm

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Testi et al. (2001)

Dust Properties or Optical Depth?

• e.g. Herbig Ae stars UX Ori, CQ Tau: 1.1-7mm~ 2.0±0.3, 2.65±0.1

~ 0 and large disk? any and small disk?

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Resolve Ambiguity

• observe spatial distribution of sub(mm) brightness• arcsecond scales require interferometry

– 1.3, 3 mm: BIMA, OVRO, PdBI, NMA; ATCA, SMA– 7 mm: VLA (thanks to CONACyT, MPIfR, NSF)

longer : lever minimizes uncertainty, probes larger dust; more concern about ionized gas

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• combine fluxes, images, improved disk models: – TW Hya– CQ Tau– 7 (2) Herbig Ae stars– 14 (10) Taurus PMS stars– 10 (5) southern PMS stars– 24 (20) Taurus/Oph PMS stars

Interferometer Studies

Calvet et al. 2002

Testi et al. 2003

Natta et al. 2004

Rodmann et al. 2006

Lommen et al. 2006

Andrews & Williams 2007

TBvs. disk radius at 0.4, 3, and 7 mm, from two dust models ofD’Alessio et al. 2001

Calvet & D’Alessio 2001

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=0.70.1

Calvet et al. 2002

Grain Growth in TW Hya

• irradiated accretion disk model matches SED and VLA (and SMA) intensities from 10’s to Rout~ 200 AU

• shallow (sub)mm slope requires amax >> 1 mm

• observed 7 mm low brightness requires << 1

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Many (Barely) Resolved Disks

VLA 7mm Rodmann et al. 2006

ATCA 3mm Lommen et al. 2006

VLA/PdBI/OVRO

Natta et al. 2004

SMA 0.87/1.3mm Andrews & Williams

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• ≤1 for many/most resolved disks

Many More Determinations

solid: Lommen et al. 2006dashed: Rodmann et al. 2006dotted: Natta et al. 2004

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is an average, for any dust model– cannot disentangle all properties <1: hard to avoid substantial mass fraction a~O()

Limitations/Complexity of

Natta & Testi 2004

1mm

0

2

1

1-7mm

Natta & Testi 2004amax

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TW Hya at 3.5 cm?

• disk model underpredicts 3.5 cm emission

• emission mechanism?– ionized protostellar wind

• if FcmdMacc/dt, low by 103x

– spinning dust (Rafikov 2006)

• requires high (unrealistic) C fraction in nanoparticles/PAHs

– synchrotron • X-rays not stellar activity: dense,

cool, and depleted accretion (Stelzer & Schmitt 2004)

– thermal dust, const

F ~ -2.60.1

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Weidenschilling 1997 Dullemond & Dominik 2005

Grain Size Evolution

• theory: growth, settling, destruction, … – depart from simple power law size distribution– create midplane population of ~cm size (timescale?)

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TW Hya: Pebble Population

toy model: small + ~cm size grains

Wilner et al. 2005

• 3.5 cm disk dust emission 1. not variable: weeks to years

2. resolved at arcsec scale, brightness only ~10 K

3. steep spectrum to 6 cm

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• no trend of with stellar luminosity, mass, age• tantalizing trends of with mid-ir growth, settling indicators

Any Correlations?

PPV: Natta et al. 2006 Lommen et al. 2006

Acke et al. 2004

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Remarks

• (sub)mm <1: compelling evidence for growth – most of original dust mass in mm size particles

• no clear trends with stellar properties• mm/cm sizes persist for Myrs

– competition between agglomeration and collisions

• are the disks we can study in the (sub)mm the ones that will never form planets? – probably not: transition disks

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Transition Disks: Inner HolesSpitzer IRS implies r~24 AU hole

“... we remain skeptical of the existence of such a large centralgap [5 AU] devoid of dust.” - Chiang & Goldreich (1999)

Calvet et al. 2005

Wilner et al. 2006

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Transition Disks: Inner Holesmid-ir implies r~4 AU hole

Calvet et al. 2002

Hughes et al., in prep

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Next Generation (Sub)mm Facilities• 10 to 100x better sensitivity, resolution, image quality• dust emission structure at 0.1 to 0.01 arcsec• precision (sub)mm spectral index maps

at the limits of ALMAWolf & D’Angelo 2005

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End