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DUSTY DEBRIS DISKS&

EXOPLANETS

DUSTY DEBRIS DISKS&

EXOPLANETS

James R. Graham

University of California, Berkeley

October 10, 2007

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Introduction

Debris Disks

&

Planets

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HOW TO DETECT PLANETS

• Voyager spacecraft “family portrait” of the solar system» Solar system observations are the initial data point for the theory of

planet formation

» Virtually all we know about exoplanets comes from indirectDoppler methods that yield three numbers: M sin i, a & e

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EXTRA SOLAR PLANETS

• Indirect methods havefound over 200exoplanets

• Is our solar systemtypical?

• How do planets form?

» “Bottom up” or “topdown”?

• Debris disks holdclues to planets & theirformation

Doppler Planets

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OBSERVATION OF A DEBRIS DISKOBSERVATION OF A DEBRIS DISK

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THE VISIBLE SKY (Galactic Coords)

Axel Mellinger, 2000

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THE INFRARED SKY (8–200 !m)

8Leinert & Gruen 1990

EMISSION FROM SOLAR ZODIACAL DUST

T ! 250 KT ! 6000 K

0.1 0.5 1.0 5 10 50 100

Wavelength (!m)

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THE “VEGA PHENOMENON”: YOUNG MAINSEQUENCE STARS WITH IR EMISSION

THE “VEGA PHENOMENON”: YOUNG MAINSEQUENCE STARS WITH IR EMISSION

Backman & Paresce 1993 PP III"The Big Three"

Fomalhaut ! Pic

Wavelength (!m)

“Discovery of a shell around Alpha Lyrae”H. H. Aumann et al. 1984, ApJL 278 23

Vega

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THE ! PIC DEBRIS DISKTHE ! PIC DEBRIS DISK

Smith & Terrile 1984

Visible light traces starlight scattered by dust

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REPLENISHED DUST DISKSREPLENISHED DUST DISKS

• ! Pic: ~ 10 Myr• Zodiacal dust: 4.55 Gyr

Kalas & Jewitt 1995

Destruction of larger bodies supply fresh dust

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THE ! PIC DEBRIS DISKTHE ! PIC DEBRIS DISK

Smith & Terrile 1984

Visible light traces starlight scattered by dust

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THE SOLAR KUIPER BELT

SKBO

Plutinos

KBO

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THE SOLAR KUIPER BELT

Art by Don Dixon (2000)

STScI May Symposium, 2005 Malhotra

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THE ! PIC DEBRIS DISKTHE ! PIC DEBRIS DISK

Smith & Terrile 1984

Visible light traces starlight scattered by dust

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PLANETS SCULPT THE SOLAR SYSTEM

• Jupiter shepherdsthe asteroids» Stable orbits

between Marsand Jupiter

» Trojan asteroids

Jupiter

17Robert H. McNaught

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SCULPTING KUIPER BELT DUST

• Pioneer 11 detected constant dust

density between 30-50 AU

• Kuiper Belt produces !m to mm

sized dust equivalent to one km-

sized comet ground up every year

» Tiny (< 0.5!m) particles are blown

out by radiation pressure

» Bound grains spiral inward by

Poynting-Robertson drag

» Temporary trapping in Neptune’s

mean motion resonances

produces azimuthal structure

» Gravitational scattering by Jupiter

& Saturn ejects most particles;

tiny fraction of KB dust enters the

inner solar systemMoro-Martin & Malhotra, 2003

STScI May Symposium, 2005 Malhotra

AU

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LESSONS FOR DUSTY DEBRIS DISKS

• Planets within debris disks sculpt the dust

distribution

With solar

system planetsWithout planets

Minimum at Neptune’s

position (to avoid resonant

planet)

Ring-like structure along

Neptune’s orbit

(trapping into mean

motion resonances)

Clearing of dust < 10 AU

(gravitational scattering

by Jupiter & Saturn)100 AU

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Fomalhaut

Probing Debris Disk Structure for

Signs of Planets

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!! PICTORIS IN PICTORIS IN SCATTEREDSCATTERED LIGHTLIGHT

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SUB-MILLIMETER TELESCOPES ON

MAUNA KEA

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The Fanatastic Four at 850 !m

20 pc20 pc 7.7 pc7.7 pc 7.7 pc7.7 pc 3.2 pc3.2 pc

JCMT/SCUBA maps of debris disk stars show intriguing structure at

sub-millimeter wavelengths—the resolution is poorHolland et al. 1998;

Greaves et al. 1998

25S

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FOMALHAUT IN CONTEXTFOMALHAUT IN CONTEXT

• Spectral type A3V

• Young & nearby

(8 pc)

• At 200-300 Myr it

may be entering

“late heavy

bombardment”

phase recorded in

the Solar System

cratering history

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SEARCHING FOR DEBRIS DISKS WITHSEARCHING FOR DEBRIS DISKS WITH

THE HUBBLE SPACE TELESCOPETHE HUBBLE SPACE TELESCOPE

• In March 2002 Hubblewas upgraded with anew camera» Advanced Camera for

Surveys (ACS)

» Coronagraphic mode ofoperation with occultingspots to block the light ofbright stars

• New opportunity toimage these elusivedebris disks at highresolution

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FOMALHAUTFOMALHAUT’’s s DISK DISCOVEREDDISK DISCOVERED

• Even with the ACS

coronagraph

blocking most of

the stellar light a

faint disk isundetectable

» Search by

subtracting an

image of Vega from

that of Fomalhaut

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Discovery

image, May 17,

2004, F814W

JCMT SCUBA

450 micron

map (Wyatt &

Dent 2002)

HST FOMALHAUT IMAGE & SUB-MM DATAHST FOMALHAUT IMAGE & SUB-MM DATA

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FOMALHAUT F814W + F606WFOMALHAUT F814W + F606W

25 mas /

pix,

FWHM =

60 mas =

0.5 AU

Kalas, Graham & Clampin 2005, Nature, June 2005

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BELT PARAMETERSBELT PARAMETERS

• Semimajor axis: 140.7± 1.8 AU

• Semiminor axis: 57.5 ± 0.7 AU

• PA major axis: 156.0˚±0.3˚

• Inclination: 65.9˚± 0.4˚

• Projected offset: 13.4 ± 1 AU

• PA of offset: 156.0˚ ± 0.3˚

• Deprojected offset: 15.3 AU

• Eccentricity: 0.11±0.04

Orbital period at 140 AU = 1200 yr

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DUST BELT SIMULATIONS

• Adam Deller &

Sarah

Maddison,

(Swinburne U.)

• 2 MJ planet

• e = 0.3

• a = 70 AU (420

yr)

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DUST BELT SIMULATIONS

• Adam Deller &

Sarah

Maddison,

(Swinburne)

• 2 MJ planet

• e = 0.3

• a = 70 AU (420

yr)

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Beta Pic’s Sibling:

AU Microscopii

What are Debris Disks Made of?

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AU Microscopii (GJ 803)• High proper motion M1Ve

flare star GJ 803

» 9.9 pc

• Discovered in the IRAS PSCwith a 60 !m excess(Tsikoudi 1988; Mathioudakis& Doyle 1991)

• Member of the ! Pic movinggroup (Barrado y Navascues1999)

» Young (12+8-4 Myr)

15 13 11 9

log("/Hz)

Kala

s &

Delto

rn (1

999)

Math

ioudakis

& D

oyle

1991

Zuckerm

an, S

ong, e

t al. 2

001

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Discovery of the Scattered Light Disk

UH 2.2-m, R-band, 900 s, seeing = 1.1"

Kala

s, L

iu, &

Matth

ew

s2004

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88-inch Telescope & CoronagraphZ

uckerm

an, G

radie

, et a

l. (UC

LA

/Haw

aii)

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! Pic & AU Mic

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F606W

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AU Mic in Polarized Light

• Two orbits Hubble/Advanced Camera in visible light» 1.’’8 Ø coronagraph spot

» Combined data from three polarizing filters at 0°, 60°, & 120°

• False color encodes brightness of scattered starlight» Ticks show orientation and strength of polarization

• To produce such high polarization the grains must befluffy or porous

1 arc sec

10 AU

Graham et al. 2007

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Porous Low Index Materials

Aerogel

• Terrestrial examplesof porous materialsare snow and aerogel» The porosity is often a

clue to how thematerial formed

» e.g., compare snowflakes (97% emptyspace; 3% ice) withhail stones (mostlysolid ice)

Dry champagne powder

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AU Mic Cartoon

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Scattering, Refraction & Polarization

• HST measures how dustgrains in orbit around AUMic scatter starlight» Reflection & refraction of light

are quantified by the refractiveindex

• When light is reflected it isselectively polarized

» Degree of polarization dependson the angles & the refractiveindex

» e.g., on a clear day skylight isstrongly polarized as is sunlightreflected off the ocean or snow

• The refractive indexdepends on the density &very low values meanporous or fluffy material

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Porous Grains

• Porous grains are anatural consequence ofvarious grain growthscenarios» Diffusion limited

aggregation

» Cluster-clusteraggregation

» Self avoiding random walk

Wrig

ht 1

987

• Porosity is a clue to the formation mechanism &processing history» Snow flakes vs. hailstones

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ACS

March 2002–January 2007

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Life After Hubble

Ground Base Telescopes &

Adaptive Optics

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Why is AO Needed?

Natural seeing AO corrected

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Why is AO

Needed?• Refractive index

variations in the

atmosphere distort

incoming wavefronts

» Swimming pool

analogy

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How to Measure Wavefront Errors

Shack-Hartmann wavefront sensor

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How a Deformable Mirror Works: I

BEFORE AFTER

Incoming

Wave with

Aberration

Deformable

MirrorCorrected

Wavefront

How a Deformable Mirror Works: II

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Mt Hamilton

Feb 2001120-inch

Telescope

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AO bench

120-inch

Telescope

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Lick/LLNL Laser

Guide Star

• Pulsed dye laser

» Nd:YAG pump

» 100 ns pulse/11 kHz

rep rate

» 11-12 W of 589 Na D2

light

55D. Whysong

Lick Laser

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LICK LASER

M. Perrin

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Na BeaconScattering by

mesospheric Na

layer at ~ 95 km

R ~ 8 mag

1.5’’ FWHM

Rayleigh back scatter

Maximum altitude of

Rayleigh ~ 35 km

48’’

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Keck Observatory

Na 589 nm Lasers at Lick & Keck

Lick Observatory

59http://en.wikipedia.org/wiki/Image:Keck_laser_at_night.png

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AU Mic Observed with Keck AO

Fitzgerald Kalas & Graham 2006

• Many debris disks are now observable

with Keck!

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Conclusions

• Transient dust is common around may stars» Solar Zodiacal & Kuiper belts

» Beta Pic disk & other debris disk stars, e.g.,Fomalhaut & AU Microscopii

• Structure of debris disks gives hints of wheretheir planets orbit

• Optical properties of dust grains suggest thatplanets grow “bottoms up”

• Rapid progress in adaptive optics now makesit possible to image debris disks from theground» In the near future instruments such at the Gemini

Observatories “Planet Imager” will see planetsdirectly!

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The End