A New “Radio Era” for Planet Forming Disks

K. Teramura UH IfA

David J. WilnerHarvard-Smithsonian Center for Astrophysics

thanks to S. Andrews, C. Qi, and many collaborators, www.cfa.harvard.edu/disks

SMA

ALMA

HIA, Victoria, March 2013

EVLA

Stars Form with Protoplanetary Disks

Marois et al. 2010, Keck Observatory

McCaughren & O’Dell 1995

Silhouette Disks in Orion Nebula around ~1 Myr-old stars

planets orbiting HR 8799

How do disks evolve and form planetary systems?

Relevance of Radio Astronomy

• low dust opacity mass, particle properties

• many spectral lines gas diagnostics, kinematics

• access cold material including disk mid-plane

• contrast with star planet-forming region

• low T, t low brightness imaging needs sensitivity

ALMA

EVLA

1mm 1mm 1m 1km 1000km <1km

Planetesimal formation Planet formation

collisionalagglomoration

gravity-assistedgrowth

gascapture

radial driftfragmentation/

bouncing

Debris

From Dust to Planets

requires growth by 14 orders of magnitudes in size in a few Myr through several physical processes…

collisional destruction

collective

effects???

Spectral Signatures of Grain Growth

• thermal dust emission Iν ∝ Bν(T) (1 - e-τν)

≈ ν2 T κν Σ Iν ∝ ν2+b

• index b is observable an diagnostic of the particle size distribution

b

amax =

1μm

1 mm

5 cm

1 m

Beckwith & Sargent 1991Miyake & Nakagawa 1993Draine 2006

see Draine 2006

ISM grains“pebbles”

2b

0

Rodmann et al 2006Ricci et al. 2010, 2011

Disks@EVLA Key Project• PI Claire Chandler (NRAO) + 17 co-Is worldwide• grain growth and substructure in protoplanetary

disks• probe last observable link in chain from ISM dust

to planets- photometry of 60+ disks at 7/9/13/50 mm- imaging of subsets, some to 50 mas = few AUBirnstiel et al. 2010

95% confidence

Isella et al. 2010RY Tau: CARMA

• global b: weak model constraints- average level of grain growth only

• resolved colors, b(r), affected by- turbulence- particle collision model- materials- radial drift efficiency

EVLA Taurus Disk Images

spectral indices

l = 9 mm (30.5 and 37.5 GHz)

θ ~ 0.7 arcsec = 100 AU

Chandler et al, in prep

UZ Tau Resolved Millimeter Colors

• radiative transfer: tn(r)

• b(r) = d log tn(r) / d log n

amax ~ 10 cm (inner disk)

amax ~ 10 mm (outer disk)

radial drift limited growth?

• disk resolved at 0.9 -9 mm

100 AU

Harris et al. 2013, also Perez et al. 2012

Isolating the Effects of Radial Drift

• thermal pressure: vgas < vKep

– small sizes: entrained by gas

– mid sizes: strong headwind– large sizes: drag is weakWeidenschilling 1977

• natural size-sorting of solids

• strong variation of gas:dust as a function of disk radius

10

The TW Hya SystemH

ST

Weinberger et al. 2002

• closest gas-rich disk system (51 pc)– M = 0.6 M, age 3-10 Myr,

– southern, isolated, viewed nearly face-on

– many studies with SMA – good model of disk physical structure

Andrews et al. 2012

Qi et al. 2008

Indirect Signature of Radial Drift1. RT model dust densities

2. assume constant gas:dust3. non-LTE model gas (CO)4. compare with data

Rosenfeld et al. 2013

Andrews et al. 2012

gas/dust size discrepancy

Signatures of Grain Growth and Drift

• empirical dependence between dust disk extent and wavelength– emission becomes more compact at longer wavelengths

• power law index of opacity, b, decreases with disk radius– maximum particle size increases with disk radius

• CO gas disk extent much larger than millimeter dust disk– dust and gas surface density profiles are decoupled

observations naturally explained if growth and inward drift of solids concentrates large particles relative to molecular gas reservoir

• planet-disk interactions also make pressure bumps/particle traps

13

Snow Lines and Planet Formation• “snow line” = boundary

where volatiles condense out of gas phase

• enhance planetesimal formation– dramatically increase available

solids– increase grain stickiness (icy

mantles)– influence bulk composition, e.g.

C/O

• key evaporation temperatures– H2O: 170 K (R = a few AU)

– CO: 20 K (R = a few 10’s of AU)

Hayashi 1981

Ciesla & Cuzzi 2006

Oberg et al. 2011

14

• disks are 3D objects: “snow line” = “snow surface” – very difficult to discern in (optically thick) CO emission

• use chemical selectivity to advantage• N2H+ abundant only where CO highly depleted

– CO inhibits N2H+ formation

– CO speeds up N2H+ destruction

– CO freezes out at 20 K– observed in pre-stellar cores

CO Snow Line and N2H+ Chemistry

Qi et al. 2012

H3+ HCO+

N2H+

CO

N2

CO

15

TW Hya SMA Obs ALMA Prediction

SMA N2H+

data

model

simulation

16

TW Hya ALMA Cycle 0 N2H+ Imaging

• N2H+ shows a ring

• 2012 November 18• l = 0.8 mm (band 7)• 26 antennas, 2 hours• beam 0.6 x 0.6 arcsec • rms = 25 mJy (0.1 km/s)

>20x better sensitivity, >20x smaller beam area than SMA N2H+ obs

- rim radius (27 AU) matches prediction for CO snow line

- N2H+ abundant where T drops below 20 K

2011.0.00340.S PI Qi

Planetesimal Belts in Debris Disks• sister stars in the 12 Myr-old b Pic Moving Group• surrounded by dusty disks, cleared of gas, viewed

edge-on

17

b PicA6

19.4 pc

Rdisk > 800 AU

AU MicM1

9.9 pc

Rdisk > 200 AUKalas 2004

18

Scattered Light Midplane Profiles

both disks show broken power-law profiles with similar slopes

Liu 2004

Golimowski et al. 2006

R-4R-1

b Pic break at R ~120 AUR-1

R-4

AU Mic break at R ~35 AU

19

The “Birth Ring” Paradigm• a collisional ring of dust-producing planetesimals

– small grains blown out by stellar radiation (b Pic) and winds (AU Mic)

– large grains stay close to birth ring– size-dependent dust dynamics explains scattered light

profile

b = F*/Fgrav

Krivov 2010 (see Wyatt 2006)

Strubbe & Chiang 2006 (also see Augereau & Beust 2006)

scattered light

20

SMA: 1.3 Millimeter Emission Belts

Wilner et al. 2011

b Pic

contours: ±2,4,6,8 x 0.6 mJy

Wilner et al. 2012

AU Mic

contours: ±2,4,6 x 0.4 mJy

21

Emission Models and Belt Locations b Pic

R = 94±8 AUDR = 34+44 AU

F = 15±2 mJy

-32

AU Mic

R = 36+7 AUDR = 10+13 AU

F = 8.2±1.2 mJy

-16

-8

22

MacGregor et al. 2013

AU Mic ALMA Cycle 0 Observations

>10x better sensitivity, >10x smaller beam area than SMA study

2011.0.00142.S PI Wilner2011.0.00274.S PI Ertel

• 4 SB executions in 2012 April and June

• l = 1.3 mm (band 6)• 16 to 20 antennas• beam 0.8 x 0.7 arcsec (8 x 7 AU)• rms = 30 μJy

23

Millimeter Emission Model Fitting

contours: ±4,8,12,.. x 30 μJy

outer belt

+central peak

24

AU Mic Outer Dust Belt Properties• extends to R=40 AU, to the break in scattered light

profile– consistent with model based on size-dependent dust

dynamics

• appears sharply truncated– reminiscent of the classical Kuiper Belt– initial condition? or result of dynamical interaction?

• surface density profile rises with radius, S(r) ~ r2.8 – collisional depletion of inner disk by ongoing planet

formation?

• no detectable asymmetries in structure or position– no significant clumps, e.g. due to resonances with orbiting

planet– centroid offset limit compatible with presence of Uranus-like

planet

Kennedy and Wyatt 2010

Mustill and Wyatt 2009

25

AU Mic Central Peak Emission

• stellar photosphere and additional unresolved emission– measure 320 mJy in central component– a NextGen stellar model (3720 K, 0.11 L 0.6 M) 52 mJy

• stellar flares? – no detectable variability, hours to months

• stellar corona? – low radio flux density limits in quiescence from VLA (in early

1990s)– requires turnover frequency > 40 GHz, or time evolution – would be detectable by EVLA at centimeter wavelengths

• asteroid-like belt at a few AU?– compatible with absence of excess emission < 25 μm– would be easy for ALMA to resolve in future Cycles

A new “Radio Era” for Disk Studies• planets form in circumstellar disks• major unknown is

distribution/evolution of cold dust and gas at Solar System scales: key observables for ALMA and EVLA

• entering a new regime of decoupled gas and dust, size-dependent dust dynamics

• three examples- resolving grain growth and drift - imaging snow lines- revealing planetesimal belts• expect surprises!

27

END

Next Generation Radio Telescopes

• 66 moveable 12m/7m antennas 5000 m site in northern Chile l = 300 mm to 7 mm

• global collaboration (NA, EU, EA) to fund >$1B construction

• 27 moveable 25 m antennas 2000 m site in New Mexico l = 7 mm to 4 m

• modern electronics and signal processing, c. 1980 infrastructure

Atacama Large Millimeter Array Expanded Very Large Array

10-100x better sensitivity, spectral capabilities, resolution

Planet-Disk Interactions• viscous/tidal

interactions make waves

• consequences– open a gap– create pressure

bumps – planet migrationGoldreich & Tremaine 1980; e.g., Bryden et al 1999

Andrews et al 2011aMathews et al 2012 Brown et al 2008 Hughes et al 2009 Andrews et al 2011a

Andrews et al 2011b

Andrews et al 2009

Transition Disk Issues • mass flow across gap

– gas: regulated by Mp + viscosity

– dust: size-dependent filtration

• particle trapping (and growth)– location of ring vs. planet orbit– azimuthal asymmetries

Lubow and D’Angelo 2006, Zhu et al. 2012, Dong et al. 2012

Pinilla et al. 2012, Birnstiel et al. 2013

ALMA Cycle 0 HD142527

Casassus et al. 2013

A New “Radio Era” for Planet Forming Disks

K. Teramura UH IfA

David J. WilnerHarvard-Smithsonian Center for Astrophysics

thanks to S. Andrews, C. Qi, and many collaborators, www.cfa.harvard.edu/disks

SMA

ALMA

HIA, Victoria, March 2013

Planetary Systems Form from Disks

Marois et al. 2010, Keck Observatory

McCaughren & O’Dell 1995

Silhouette Disks in Orion Nebula around ~1 Myr-old stars

planets orbiting HR 8799