The Cradle of Life:

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The Cradle of Life Proto-planetary Disks
Square Kilometer Array
Sean M. Dougherty (NRC) David J. Wilner (CfA)
Courtesy Geoff Bryden
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Why Cradle of Life?

• Recent discovery of extra-solar planets
• 120 exo-solar planets - many gas giants
• Are there other Earth-like planets?
• publicly enthralling, scientifically
  philosophically important in 21st century
• NASA Origins
• Kepler (2007) transit photometry
• SIM (2009) optical interferometer --
  astrometry
• TPF (2015) optical chronograph/ IR-nulling
  interferometer
• These are planet finders
• How common are Solar Systems like our own?
• Are terrestrial planets common?
• What accounts for the diversity of planetary
  systems?

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Why Cradle of Life? (cont)

• Relevance of Proto-planetary Disks -
  proto-planetary gt enough gas to form giant
  planets
• - planet formation
• inner disk within 1AU of the central star
  the habitable zone
• Planet formation within 1 AU . The Cradle of
  Life
• - accretion physics
• Disks are Naturally multi-l Objects
• T,n,B. f(r,f,z) ? phenomena _at_ many
  wavelengths
• driver for JWST/ALMA/TMT, etc.
• And the SKA..
• Only instrument capable of imaging dust emission
  within 1AU
• - the birth of planets within 1AU

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Planet Building

• Observe young stellar systems to identify
• 1. physical processes
• grain growth, orbital migration of grains
• 2. signatures of planets in formation
• disk structure gaps, evolution
• There are large numbers (100s) of
  proto-planetary disks at 140 pcsize scale of
  regions relevant for planets lt 10 AU lt 70 mas
• terrestrial planets lt 1AU lt 7 mas

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State-of-the-Art Disk Imaging
TW Hya _at_ 56 pc
Hubble Space Telescope optical scattered light
(Schneider et al. 2001)
VLA 7mm dust emission (Wilner et al. 2000)
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Example the DG TAU Proto-stellar System

• well-studied, very
• active, T Tauri star
• optical jet P.A. 226
• VLAPT at 7 mm
• sees inner dust disk,
• q 35 mas, DK 20
• Where is the star?
• What produces the
• asymmetry?

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Physical Models of Disk Structure

• Physical models now taking
• place of power law
• parameterizations

• self-consistent treatment of
• radiative and hydro-static
• equilibrium using radiative
• transfer

S(r)
T(r)
h(r)
e.g. Chiang Goldreich 1997, 99
DAlessio et al. 1997, 98 , 99...
Dullemond et al. 2000, 01, 02...
SED
DAlessio et al. 2001
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TW Hya an eVLA Simulation

• physical model of
• irradiated accretion
• disk adapted from
• Calvet et al. (2002)
• ApJ, 568, 1008
• VLA Pie Town
• configuration, 7 mm
• eVLA PT could
• image 4 AU radius
• hole (if it exists)

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Are Proto-planetary Gaps Detectable?
VLTI _at_ 10 mm
ALMA _at_ 700 mm
Hydro simulations of disk _at_ 140pc with an
embedded Jupiter-mass planet The gap lies 37 mas
(5.2 AU) from the star. To image within lt 4-5
AU, need longer wavelengths
Wolf et al. 2002
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Evidence for Grain Growth in Disks

• at long ls where tlt1,
• F kdust l-2 l-(b2)
• so radio/mm data provide
• direct measure of b
• diagnostic of grain characteristics
• (size, composition etc.)

• compact, spherical particles
• a ltlt l, b2
• pebbles, rocks, asteroids
• a gtgt l, b0

Beckwith and Sargent 1991
If F l-2 , then large grains? or compact
structure with tgt1?
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Example Large Grains in CQ Tau

• CQ Tau
• M 1.5 Mo, age 10 Myr
• spectral index
• 1 mm to 7 mm 2.4
• 7 mm - resolved by VLA
• models indicate
• t lt 1 for r gt 8 AU,
• R 200 AU (p1),
• kdust l-0.6
• most of dust mass in
• cm- size grains

Testi et al. 2003
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Next Generation High Resolution Imaging
TMT scattered light q 13 mas x (1.6 mm/30
m) (and infrared spectroscopy that probes inner
disks indirectly) ALMA dust emission q 13 mas
x (345 GHz/18 km) (molecular lines at lower
resolution) long ls (cm) dust emission gt low
dust opacity gt penetrate inner disks SKA q
1 mas x (24 GHz/2500 km) for rms 10 K at q 1
mas, need rms 20 nJy EVLAII q 7 mas x (24
GHz/360 km)
TW Hya
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Cradle of Life SKA specs.

• Terrestrial Planet formation within 1AU
• planets (gas giants) found within this radius
• several resolution elements to cover 1AU _at_
  140pc
• 1 mas gt 0.14 AU _at_ 140pc
• High frequency compromise between rapidly
  increasing flux, increasing opacity (
  resolution)
• 20-30 GHz
• Imaging dust of 50-300 K.
• Continuum brightness sensitivity 10K
• For q 1 mas (2500 km _at_ 24 GHz), rms 10 nJy
  gives 10K

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SKA could play Unique Role in Disk Studies

• If capable at gt 20 GHz, SKA will have best
  resolution/sensitivity
• for imaging thermal emission.
• For direct detection of structure
• in disks induced by planets,
• sub-AU resolution is key.
• (synergy with other facilities)
• High angular resolution probes
• terrestrial planet region and
• enables following evolution
• over orbital timescales.
• Short centimeter wavelengths
• are critical for tracking grain growth from
  sub-micron
• interstellar size particles to pebbles.

Bate et al. 2003