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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