1
ALMA View of Dust Evolution: Making Planets and Decoding Debris
David J. Wilner (CfA)
Grain Growth → Protoplanets → Debris
2
“Protoplanetary” to “Debris” Disks
• <1 to ~10 Myr• gas and trace dust
– gas dynamics (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
– dust dynamics (radiation, collisions)
– <1 Mmoon
• excess: mainly far-ir/mm• planetesimals are colliding
and creating dust particles
SM
A Isella et al. 2006
CSO Marsh et al. 2005
3
Disk Dust and ALMA
• longest observable λ’s: 0.35 to >3 mm• “vibrational” emission is dominant mechanism
(thermal fluctuations in charge distribution)• unprecedented sensitivity, resolution, calibration
• sensitive to “cold” dust: T<10’s of K• if low opacity, then flux ~ Mdust weighted by Tdust
• wavelength dependence of mass opacity diagnostic of particle properties, esp. grain size
• no contrast problem with stellar photospheres
4
• collisional growth– subµm to mm sizes stick at <1 m/s
– • from m to km sizes?
– too large for chemistry, too small for gravity– collective effects, e.g. layers? vortices? spiral waves?
Blum et al. 1998, 2000C. Dominik
SiO2
The Beginning: Particles Stick
QuickTimeª and aYUV420 codec decompressor
are needed to see this picture.
5
• dust mass opacity model, e.g. power law• flux density emitted by disk element dA
• mm data: disk β~0 to 1 (large grains) vs. ISM β~2 (Rayleigh limit)• concern with optically thick contribution
Spectral Signatures of Growth
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
Beckwith & Sargent
1991
6
• combine physical model, fluxes, resolved data– irradiated accretion disk (Σ~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
Example: TW Hya
β=0.7±0.1
Qi et al. 2004, 2006
Calvet et al. 2002
VLA 7 mm
SMA 0.87 mm
SED
7
Many Resolved Disks, β Measures
ATCA 3mm Lommen et al. 2006
VLA/PdBI/OVRO Natta et al. 2004
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))
8
ALMA: Resolved Disk “Colors”• precision subarcsec spectral index information
– couple with disk structure models to account for opacity and temperature variations, localize grain growth
S. Andrews
no growth
“inside-out”grain growth
9
Millimeter Sizes Persist Myrs
• much longer timescale than <<0.1 Myr theory predicts
• competition between growth and destruction processes?
• grain size (opacity) need not follow a simple power law
• are the disks we can study in the millimeter the ones that will never form planets? – probably not: transition disks
Weidenschilling 1997
Dullemond & Dominik 2005
10
• 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– planet formation? viscous evolution and photoevaporation?
Calvet et al. 2005
“gap”
inner disk with bit of ~µm dust
r~24 AU inner edge of outer disk
Bryden et al. 1999
Transition Disks
~2 Myr, M*=0.84, Md~0.09 M
11
Example: GM AurCO 2-1 IRAM PdBIDutrey et al. 1998
Schneider et al. 2003
230 GHz IRAM PdBI
12
Debris Disks
• discovered in far-ir:– ~15% of main sequence
stars show “debris”: IRAS, ISO, Spitzer
• ~10 disks 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
Smith & Terrile 1984
13
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
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:
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, blown out
3:2Wyatt 2006
VegaH
olland et al. 1998
Su et al. 2005
850 µm70 µm 24 µm
15
Example: Vega (350 Myr, A0V, 7.8 pc)
• like Neptune migration (Wyatt 2003)?�∆a ~7 AU over ~50 Myr (Hahn & Malhotra 1999)
QuickTimeª and aYUV420 codec decompressor
are needed to see this picture.
Wyatt 2003
Minor Planet Centerwhite: 2:1 Plutinos
16
• sensitivity limited with existing facilities• the archetype Vega at 1.3 mm
– compatible images (poor SNR and uv coverage)– dust blobs are robust, spatially extended– stellar photosphere (2 mJy) provides calibration check
Higher Angular Resolution?
IRAM PdBI: Wilner et al. 2002 OVRO: Koerner et al. 2001
17
• Vega is north (+38 dec) but visible with ALMA
An ALMA Simulation
thanks to J. Pety
• compact configuration: 2x1 arcsec @ 350 GHz
• low surface brightness (model) disk emission– 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
model image
fidelitydifference
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?
∀ ε Eri rotation ~1”/yr detected (2σ)? (Greaves et al. 2005)
see Wilner et al. 2002 and Moran et al. 2004
19
Planet Parameter Space
• debris disk structure probes long periods
• complementary to classical techniques
period→←m
ass
20
Summary
• ALMA will qualitatively change nature of dust observations from disks, all evolutionary stages
• Protoplanetary Disks– grain growth from
resolved “colors”• Transition Disks
– image holes, etc.• Debris Disks
– locate planets with resonant particles
– fossil record of planet dynamics
QuickTimeª and aYUV420 codec decompressor
are needed to see this picture.
NASA/ R. Hurt