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Transcript
ALMA View of Dust Evolution:
Making Planets and Decoding Debris
David J. Wilner (CfA)
Grain Growth 
Protoplanets 
Debris
1
ALMA and Dust Emission
• “vibrational” emission is dominant mechanism
(thermal fluctuations in charge distribution)
• longest observable ’s: 0.35 to >3 mm
• sensitive to cold dust: T<10’s of K
• samples all disk radii/depths
• if low opacity, then flux ~ Mdust weighted by Tdust
• wavelength dependence of opacity is diagnostic
of particle properties, esp. grain size
• no contrast problem with stellar photospheres
• unprecedented sensitivity and angular resolution
2
“Protoplanetary” to “Debris” Disks
CSO Marsh et al. 2005
SMA Isella et al. 2006

• <10 Myr
• gas and trace dust
– dynamics dominated by
gas (hydro, turbulence)
• ~0.001 to 0.1 M
• excess: near/mid/far-ir/mm
• dust particles are sticking,
growing into planetesimals
• up to Gyrs
• dust and trace gas
– dynamics dominated by
dust (radiations, collisions)
• <1 Mmoon
• excess: mainly far-ir/mm
• planetesimals are colliding
and creating dust particles
3
The Beginning: Particles Stick
• collisional growth
– subm to mm sizes stick at <1 m/s
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
SiO2
–
• to km sizes?
C. Dominik
Blum et al. 1998, 2000
– too large for chemistry, too small for gravity
– collective effects, e.g. layers? vortices? spiral waves?
4
Spectral Signatures of Growth
• dust mass opacity model, e.g. power law
• flux density emitted by disk element dA
• mm: disk ~0 to 1 vs. ISM ~2 (Rayleigh limit)
Pollack et al. 1994 mixture,
compact, segregated spheres,
n(a) ~ a-q, q=3.5
amax=1 mm
amax=10 cm
Calvet & D’Alessio 2001
Beckwith
& Sargent
1991
5
Example: TW Hya
• combine physical model, fluxes, resolved data
– irradiated accretion disk model (~r-1,T~r-0.5) matches
(a) SED and (b) resolved 7 & 0.87 mm continuum
– shallow mm slope and low brightness require amax > 1 mm
SMA
0.87 mm
=0.70.1
SED
Calvet et al. 2002
VLA
7 mm
Qi et al. 2004, 2006
6
Many Resolved Disks,  Measures
ATCA 3mm Lommen et al. 2006
solid:
Lommen et al. 2006 (10 southern pms stars)
dashed: Rodmann et al. 2006 (10 Taurus pms stars)
dotted: Natta et al. 2004 (7 Ae stars + TW Hya, CQ Tau))
VLA/PdBI/OVRO Natta et al. 2004
7
ALMA: Resolved “Colors”
• precision subarcsec spectral index information
– couple with disk structure models to account for opacity
and temperature variations, localize grain growth
no growth
inside-out
growth
S. Andrews
8
Millimeter Sizes Persist Myrs
• much longer timescale than
theory predicts (<1000’s yr)
• competition between growth
and destruction processes?
• grain size (opacity) need not
follow a simple power law
Weidenschilling 1997
• are the disks we can study in
the millimeter the ones that will
never form planets?
– probably not: transition disks
Dullemond & Dominik 2005
9
Transition Disks
• all indicators of circumstellar material decline, t ~ 5 Myr
• GM Aur, TW Hya, CoKu Tau 4, DM Tau, …
– near/mid-ir flux deficits indicate inner holes (Spitzer)
– planet formation? viscous evolution and photoevaporation?
r~24 AU inner edge of outer disk
~2 Myr, M*=0.84, Md~0.09 M
“gap”
Calvet et al. 2005
Bryden et al. 1999
inner disk with bit of ~m dust
10
Embedded Protoplanets
• protoplanet interacts
tidally with disk
–
–
–
–
transfers ang. momentum
opens gap
viscosity opposes
evolve inner holes
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
• very active area
– viscosity not understood
– disk structure not known
– inbalance of torques leads
to planet migration
P. Armitage
11
Example: GM Aur
CO 2-1 IRAM PdBI
Dutrey et al. 1998
230 GHz IRAM PdBI
12
Debris Disks
Smith & Terrile 1984
• discovered in far-ir:
– ~15% of main sequence
stars show excess:
IRAS, ISO, Spitzer
• ~10 imaged in
scattered light and/or
thermal emission
– highly structured
– inner holes, clumpy
rings, warps, spirals,
offsets, asymmetries
– sculpted by planets?
Holland et al. 1998
Greaves et al. 1998
13
Resonant Perturbations
• Pres = Pplanet (p+q)/p, planet gives periodic kicks
• structure created when resonances filled by
– inward migration of dust due to P-R drag
– outward migration of planet traps planetesimals
• e.g. simulation of dust in our Solar System:
no planets
planets
– KB dust drifts in
– clumpy ring around
orbit of Neptune;
3:2  two clumps
(cf. “Plutinos”)
– nearly empty inner
hole due to Jupiter
Liou & Zook 1999
14
Large Dust  Small Dust
• structure depends on Frad/Fgrav
– largest grains retain resonant parent distribution
– intermediate grains librate widely, smooth out
– smallest grains are unbound and blown out
3:2
Wyatt 2006
70 m
24 m
Su et al. 2005
Vega
Holland et al. 1998
850 m
15
Fossil Record of Planet Dynamics
• Vega: analogous to Neptune migration?
 a ~7 AU over ~50 Myr (Hahn & Malhotra 1999)
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Minor Planet Center
Wyatt 2003
16
Higher Angular Resolution?
• sensitivity limited with existing facilities
• the archetype: Vega (350 Myr, A0V, 7.8 pc) at 1.3 mm
IRAM PdBI: Wilner et al. 2002
OVRO: Koerner et al. 2001
– compatible images (poor SNR and uv coverage)
– dust blobs are robust, spatially extended
– stellar photosphere (2 mJy) provides calibration check
17
An ALMA Simulation
• Vega is north (+38 dec) but visible from ALMA site
model
image
• compact configuration:
2x1 arcsec @ 350 GHz
• low surface brightness
(model) disk emission
difference
fidelity
–
–
–
–
mosaic essential
ACA essential
total power essential
careful treatment of
bright star (5 mJy) in
imaging and deconv.
• high fidelity challenging
for large, nearby disks
thanks to J. Pety
18
Synoptic Studies
• resonant structures
rotate around star
• multi-epoch imaging
– follow motions of
clumps to distinguish
models (and exgal.
background sources)
– Vega: a circular
Neptune or an
eccentric Jupiter?
  Eri rotation ~1”/yr
detected (2?
(Greaves et al. 2005)
see Wilner et al. 2002 and Moran et al. 2004
19
Summary
• ALMA will qualitatively
change nature of dust
observations from disks,
all evolutionary stages
• Protoplanetary
– grain growth from
resolved “colors”
• Transition Disks
– image gaps, holes,
related structures
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
• Debris Disks
– locate planets with
resonant particles
NASA/ R. Hurt
20
End
21
Schematic Solar System Evolution
10
105 yr
protostar
+ primordial
disk
Lstar
planet building
protoplanetary disk
107 yr
109 yr
1
104 yr
planetary system
+ debris disk
100 AU
cloud collapse
8,000
5,000
2,000
Tstar (K)
adapted from Beckwith & Sargent 1996, Nature, 383, 139
22
G,K stars within 4 pc
• 3 binaries, 2 debris disks (r~60 AU), and the Sun
0.8 Gyr
61 Cyg
Sun
<10-5 ME
 Eri
10-2 ME
Greaves et al. 2005
7.2 Gyr
t Cet
5x10-4 ME
a Cen
 Ind
Greaves et al. 2004
23
Planet Detection Parameter Space
mass
• debris disk structure
probes long periods
• complementary to
classical techniques
period
24