Decoding Dusty Debris Disks

AAAS, Februrary 2014

David J WilnerHarvard-Smithsonian Center for Astrophysics

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Debris Disk Primer

• far-infrared surveys of nearby stars reveal thermal dust emission from reprocessed starlight, Fdust/F* < 10-3

Stapelfeldt et al. 2004

Fomalhautstar

dust

images show disks

Hu

bb

le, K

ala

s et a

l. 20

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dust must be replenished reservoirs of large bodies

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Descendents of Protoplanetary Disks

Protoplanetary Disk Debris Diskage < 10 Myr 10 Myr to 10 Gyrdust mass > 10 MEarth < 0.1 MEarth

gas mass 100x dust mass << dust massphysical picture

primordial dust colliding, growing into planetismals

planetismals colliding, generating secondary dust

Fomalhaut

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The Solar System Debris Disk

• Kuiper Belt (42-48 AU) and asteroid belt (2-3.5 AU)• dust-producing bodies in stable belts and

resonancesESA

A. Felid/STScI

encodes planetary system architecture and dynamical history

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Debris Disks and Planetary Systems• outcomes of planet formation• Solar System configuration in

context• planet detection from disk

perturbations• habitability of terrestrial planets

Fomalhaut

b Pictoris

HR 8799

HD 95086

HD 106906

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Millimeter Emission traces Planetesimals• 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/JAXA

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20 Myr-old Sister Stars with Debris Disks

b Pictoris

Roptical > 800 AU

AU Microscopi

Roptical > 200 AUKalas 2004

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Scattered Light Midplane Profiles

“birth-ring” of planetesimals predicted at break in power-law profile

Keck, Liu 2004

Hubble, Golimowski et al. 2006

b Pic break at R =130 AU

AU Mic break at R = 40 AU

Strubbe & Chiang 2006

scattered light

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ALMA Reveals Millimeter Emission Belts

Dent et al., submitted

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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AU Mic Millimeter Emission Modeling

contours: ±4,8,12,.. x 30 μJy

outer belt

+central peak

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• outer edge at 40 AU, matches break in scattered light profile

• surface density of planetesimals rises with radius, an outward wave of planet formation?

• no detectable asymmetries in structure or position (still compatible with presence of a Uranus-like planet)

AU Mic Outer Dust Belt Properties

T. Pyle/NASA

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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 et al. 2014

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AU Mic Higher Resolution Simulations

• easy to resolve an asteroid belt with 0.25 arcsec resolution

• a stellar corona will remain unresolved

• we’ll find out from ALMA in Cycle 1 (PI M. Hughes)

Inner Dust Belt Stellar Corona

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ALMA Observes (half) the Fomalhaut Disk

• millimeter emission belt narrower than optical scattered light

Boley et al. 2012Hubble (blue) ALMA (orange)

planetesimals confined by shepherding planets?

Saturn F Ring

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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

• sputtering? colliding Mars-mass bodies?

Dent et al., submitted

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HD 10647: A Very Dusty Debris Disk• similar to our Solar System

– Sun-like star, F9V type– a Jupiter-like planet at 2 AU– 1000x Kuiper Belt dust at 80 AU

What could ALMA see (in an hour)?

Stapelfeldt et al. 2007Liseau et al. 2010

ALMA Cycle 2 simulations

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Summary

• debris disks result from collisional cascades of planetesimals, relics of planet formation

• millimeter emission traces the planetesimals

• early ALMA observations reveal Kuiper-like belts and (the first of many) surprises

ESA

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END