Grain Growth in Protoplanetary Disks: the SubMillimeter

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Grain Growth in Protoplanetary Disks the
(Sub)Millimeter
David J. Wilner Harvard-Smithsonian Center for
Astrophysics
Sep 11, 2006
From Dust to Planetesimals, Ringberg
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(Sub)Millimeter?

• longest observable ?s for dust 0.35 to gt1 mm
• vibrational dust emission is dominant mechanism
  (thermal fluctuations in charge distribution)
• sensitive to cold dust, Tlt10s 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

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(Sub)Millimeter Observables

• T Tauri, Herbig Ae stars (dlt150 pc, 1-10 Myr)
• gas rich, Keplerian disks (Mdiskltlt M)
• submm flux vs. wavelength, F ?-?, 2 lt ? lt 4
• spatially resolved brightness (interferometer)

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Basics of ?

• mass opacity (? gt0.1 mm) approx. power law
• normalization, power
  law index ?, depend
  on dust
  properties
• composition
• size distribution
• geometry
• (e.g. Draine 2006)

??-2
Adams et al. 1988, following Draine Lee 1984
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From ? to ?

• flux density emitted by an element dA
• if ?ltlt1 and h?ltltkT, then
• and ? simply related to ?

F ?-(2?)
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Disk Dust appears Different

• early (sub)mm obs disk lt?gt1 vs. ISM ?1.7
• (e.g Weintraub et al. 1989, Adams et al. 1990,
  Beckwith et al. 1990, Beckwith Sargent 1991,
  Mannings Emerson 1994)

Beckwith Sargent (1991)
?d(?-2)(1?)
0 1 2
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?1 Interpretations

• 1. changes in dust properties
• grain growth
• small, a ltlt ?/2? ? ?2
  
• large, a gtgt ?/2? ? ?0
• mm size, ?1
• ? ?-1 due to
• dust composition,
• particle geometry
• 2. optically thick emission
• F ?-2 (in part) ? ? gt (? - 2)

Pollack et al. 1994 mixture, compact,
segregated spheres, n(a) a-q,
q3.5
amax1 mm
amax10 cm
Calvet DAlessio 2001
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Dust Properties or Optical Depth?

• e.g. Herbig Ae stars UX Ori, CQ Tau
• ?1.1-7mm 2.00.3, 2.650.1
• ? 0 and large disk? any ? and small disk?

Testi et al. (2001)
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Resolve Ambiguity

• observe spatial distribution of sub(mm)
  brightness
• arcsecond scales require interferometry
• 1.3, 3 mm CARMA, 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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Interferometer Studies

• 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

• 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 of DAlessio et al. 2001
Calvet DAlessio 2001
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Grain Growth in TW Hya

• irradiated accretion disk model matches SED and
  VLA (and SMA) intensities from 10s to Rout 200
  AU
• shallow (sub)mm slope requires amax gtgt 1 mm
• observed 7 mm low brightness requires ? ltlt 1

?0.7?0.1
Calvet et al. 2002
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Many (Barely) Resolved Disks
ATCA 3mm Lommen et al. 2006
SMA 0.87/1.3mm Andrews Williams
VLA/PdBI/OVRO Natta et al. 2004
VLA 7mm Rodmann et al. 2006
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Many More ? Determinations

• ?1 for many/most resolved disks

solid Lommen et al. 2006 dashed Rodmann et
al. 2006 dotted Natta et al. 2004
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Limitations/Complexity of ?

• ? is an average, for any dust model
• cannot disentangle all properties
• ?lt1 hard to avoid substantial mass fraction
  aO(?)

amax ?
Natta Testi 2004
Natta Testi 2004
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TW Hya at 3.5 cm?

• disk model underpredicts 3.5 cm emission

• emission mechanism?
• ionized protostellar wind
• if Fcm?dMacc/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 ?-2.6?0.1
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Grain Size Evolution

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

Weidenschilling 1997
Dullemond Dominik 2005
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TW Hya Pebble Population

• 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

Wilner et al. 2005
toy model small cm size grains
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Any ? Correlations?

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

? ?
Acke et al. 2004
??
Lommen et al. 2006
PPV Natta et al. 2006
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Remarks

• (sub)mm ?lt1 compelling evidence for growth
• most of original dust mass in mm/cm size
  particles
• no clear trends with stellar properties
• mm/cm sizes persist for Myrs
• competition between growth and destruction
• are the disks we can study in the (sub)mm the
  ones that will never form planets?
• probably not transition disks

PPV Natta, Testi, Calvet, Henning, Waters
Wilner, astro-ph/0602041
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Transition Disks Inner Holes
Spitzer IRS implies r24 AU hole ... we remain
skeptical of the existence of such a large
central gap 5 AU devoid of dust. -
Chiang Goldreich (1999)
Calvet et al. 2005
Wilner et al. 2006
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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

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End