New Views of Planet-Forming DisksRadio Imaging from SMA to ALMA

David J. WilnerHarvard-Smithsonian Center for Astrophysics

K. Teramura UH IfA

Wesleyan University November 5, 2014

http://www.cfa.harvard.edu/disks C. Qi, K. Oberg, S. Andrews, M.

MacGregor +many others

SMA

ALMA

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1. Disks and Radio Astronomy

2. Snow Lines3. Planetesimal Birth Rings

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1. Disks and Radio Astronomy

2. Snow Lines3. Planetesimal Birth Rings

Circumstellar Disks

John Bally

• inevitable consequence of collapse + angular momentum

• integral component of star and planet formation paradigmOrion “Proplyds”

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

Planetesimal formation Planet formation

collisionalagglomoration

gravity-assistedgrowth

gascapture

radial driftfragmentation/

bouncing

Debris

From Dust to Planets and Debris

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

collisional destruction

collective

effects???

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Disks Evolve and Form Planetary Systems

Protoplanetary Disk Debris Disk + Planetsage < 10 Myr > 10 Myr dust mass > 10 MEarth < 0.1 MEarth

gas mass 100x dust mass << dust massphysical picture

primordial dust colliding, growing into planetesimals

planetesimals colliding, generating secondary dust

Silhouette Disks in Orion Nebula around 1 Myr-old stars HR 8799 Solar System

Marois et al. 2010 Copernicus 1543McCaughren & O’Dell 1995

Relevance of Radio Astronomy • low dust opacity

mass, particle properties

• access cold material including disk midplane

• many spectral lines, heterodyne R~107 gas diagnostics, kinematics

• contrast with star planet-forming region

• low T, t low brightness imaging needs sensitivity

The ALMA Revolution

54 moveable 12m antennas + 12 moveable 7m antennas

5000m site in Chilean Andes

wavelengths 0.3 to 3.4mmbaselines to 16 kmglobal (NA/EU/EA)

collaboration to fund $1.3B construction

8 moveable 6m antennas

4000m site on Mauna Kea, HI

wavelengths 0.4 to 1.7mm

baselines to 0.5 kmSAO/ASIAA collaboration

25x better sensitivity and resolution!

ALMASMA

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1. Disks and Radio Astronomy

2. Snow Lines3. Planetesimal Birth Rings

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Snow Lines and Planet Formation• “snow line” = boundary where volatiles condense out

of gas phase

Hayashi 1981

H2O snow line

icy grainsbare grains

rocky planetesimal

sicy

planetesimalsRocky

Planets Gas GiantsIce Giants

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Snow Line Implications

Oberg et al. 2011

• enhance planetesimal formation– dramatically increase available solids– increase grain stickiness (icy mantles)

• multiple snow lines from species with low condensation temps

• influence planetesimal bulk composition- C/O in planetary atmospheres- H2O on planets (habitability)

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• radial and vertical gradients • CO “snow line” = CO “snow surface”

- impossible to discern in (optically thick) CO emission

- may be teased out with a disk structure model and extensive analysis of resolved multi-transition, multi-isotope CO data (Qi et al. 2011)

Disks are 3D Objects

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CO Snow Line and N2H+ Chemistry• use chemical selectivity to advantage• N2H+ is abundant only where CO highly

depleted– CO inhibits N2H+ formation– CO speeds up N2H+ destruction – CO freezes out at about 20 K

– observed in pre-stellar cores

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Chemical Effect of CO Freeze-Out

HCO+

H2CO

N2H+

T > CO freeze-out

T < CO freeze-out

N2H+

HCO+

H2CO

K. Oberg

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CO Depletion in Pre-Stellar Cores

• N2H+ and CO anti-correlated in cold, dense cores

Lada and Bergin 2003

Bergin et al. 2002

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The TW Hya Disk System W

einberger et al. 2002

• closest gas-rich circumstellar disk (~50 pc)– M* ~ 0.8 M, age 3-10 Myr, – southern, isolated, viewed nearly face-

on – many studies with the SMA – good model of (outer) disk physical

structure

Qi, Wilner et al. 2008, Andrews, Wilner et al. 2012

Hughes, Wilner et al. 2011

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TW Hya SMA N2H+ Data and Model 2012.0.00681.S PI Qi

Pro

posa

l Reje

cted

!

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• stuck N2H+ J=4-3 line into free spw of Cycle 0 program– noted in proposal with no justification– higher excitation transition, not optimal for cold mid-

plane– lower angular resolution and less sensitivity…

ALMA N2H+ Imaging 2011.0.00340.S PI Qi

• observations– 2012 Nov 18– 372 GHz– 26 antennas, 2h– 0.6x0.6 arcsec– rms 25 mJy (0.1

km/s)Qi, Oberg, Wilner et al. 2013

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Quantifying the N2H+ Ring Structure

• assume N2H+ power-law radial abundance profile

• RATRAN, fit for Rin, Rout, index

• Rin = 30 AU CO snow line

• TCO freeze-out ~18 K

Qi, Oberg, Wilner et al. 2013

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ALMA N2H+ Channel Maps

Data

Model

Residual

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Snow Lines in Protoplanetary Disks

• a series of “snow lines” arise from condensation fronts– impacts planetesimal formation and composition

• enhanced N2H+ abundance expected at CO freeze-out– a robust chemical marker for CO snow line

ALMA imaging of TW Hya CO snow line at 30 AU validates concept

• easy to extend to probe thermal effects and chemistry, e.g. do complex organics emerge from CO ice?

• need to identify chemical marker(s) for the H2O snow line

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Origins of Organics in Disks2013.0.00114.S PI Oberg

• H2CO and CH3OH form from hydrogenation of CO ice

• but H2CO may also form through gas-phase pathways

• given the location of CO snow line, easy to discriminateCycle 2 simulations of TW Hya H2CO 31,2-21,1 emission (241.7 GHz)

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Hints of CO Ice Regulated Chemistry

H2CO excitation temperature is low (< 20 K) in SMA sample of disks

Qi, Oberg, Wilner 2013

SMA images of HD 163296

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1. Disks and Radio Astronomy

2. Snow Lines3. Planetesimal Birth Rings

Planetesimal Belts in Debris Disks• sister stars in the 20 Myr-old b Pic Moving Group• surrounded by tenuous dusty disks viewed edge-

on

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b PicA6

19.4 pc

Rdisk > 800 AU

AU MicM1

9.9 pc

Rdisk > 200 AUKalas 2004

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Scattered Light Midplane Profiles

Keck, Liu 2004

Hubble, Golimowski et al. 2006

b Pic break at R =130 AU

AU Mic break at R = 40 AU

both disks show broken power-law profiles with similar slopes

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The “Birth Ring” Paradigm• collisional cascade

creates smaller and smaller fragments

• micron-size dust blown out

• large dust can’t travel far

b = F*/Fgrav

Krivov 2010

Nature/ISAS/JAXAmillimeter emission traces planetesimals

Strubbe & Chiang 2006

scattered light

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SMA b Pic Millimeter Emission Belt

Wilner et al. 2011

b Pic

contours: ±2,4,6,8 x 0.6 mJy

b Pic

R = 94±8 AUDR = 34+44 AU

F = 15±2 mJy-32

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SMA AU Mic Millimeter Emission Belt

Wilner et al. 2012

AU Mic

contours: ±2,4,6 x 0.4 mJy

AU Mic R = 36+7 AUDR = 10+13 AU

F = 8.2±1.2 mJy

-16 -8

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MacGregor, Wilner 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

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AU Mic Millimeter Emission Modeling

contours: ±4,8,12,.. x 30 μJy

outer belt

+central peak

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• 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

• surface density of planetesimals rises with radius, S(r) ~ r2.8 – collisional depletion by outward wave of planet formation?

AU Mic Outer Dust Belt Properties

Kennedy and Wyatt 2010

Kenyon and Bromley 2004

• 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

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AU Mic Central Peak Emission• unresolved and 6x stronger than stellar photosphere• stellar corona? models can match millimeter and X-ray

• asteroid-like belt at R<3 AU? compatible with infrared limits

Cranmer, MacGregor, Wilner 2014

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AU Mic Higher Resolution Simulations

• easy to resolve an asteroid belt with longer baselines• a stellar corona will remain unresolved

Inner Dust Belt Stellar Corona

• we’ll find out from Meredith Hughes’s ALMA Cycle 1 program

New Views of Planet-Forming Disks• planets form in circumstellar disks • major unknown is distribution/evolution of cold

dust and gas at Solar System scales: key observables for ALMA

• examples- imaging the CO snow line- revealing planetesimal belts

• expect surprises!

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END

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Snow Line Implicationse.g. exoplanet chemistry and spectroscopy

Mudhusudhan 2012

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Secondary Molecular Gas in b Pictoris

• ALMA detects CO J=3-2 emission • 30% from one compact clump• icy planetesimals shattered by

collisions?– destruction of large comet every 5

minutes– trapping in the resonances of an

outer planet could account for localized gas production

• colliding Mars-mass bodies?

Dent et al. 2014

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ALMA Reveals Millimeter Emission Belts

Dent et al. 2014

b PicRmm=130 AU MacGregor et al. 2013

AU MicRmm = 40 AU

Cycle 0, 20+ antennas, 2 hours, <1 arcsecond resolution

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Comet 17P/Holmes 2007 Outburst• an ordinary Jupiter family comet• discovered in 1892 during routine

monitoring of Andromeda galaxy• orbital period 6.9 years• origin believed to be in Kuiper Belt,

transported by planet migration• largest cometary outburst ever seen

(magnitude 17 to 2.8 in 42 hours)

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Outburst Significance• provides opportunity to measure chemical

abundances• unprocessed material from interior of the nucleus

is released

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October 26-29, 2007 Millimeter Continuum• resolution 2.5 - 4

arcsec (3000 - 4700 km)

• traces millimeter-sized grains in the coma

• peak locates nucleus

• dM/dt = 2.6x106 kg/s

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October 26-29, 2007 Integrated Spectra

• detect HCN, CO, H13CN, H2CO, H2S, CH3OH, CS• HCN linewidth of about 1 km/s due to outgassing• CO (and CS) narrow and offset from cometocentric

velocity

Posterior Probability Distributions

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Consistent with SMA CO Isotope Data

SMA observations of13CO and C18O J=2-1

CO freeze-out