Pinpointing Planets in

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Pinpointing Planets in Circumstellar Disks
Alice Quillen University of Rochester
Mar 2009
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3 Systems hosting disks with clearings
Age Mass Type Distance Radius of clearing
CoKuTau4 1-2 Myr 0.5M? M 140 pc 10 AU
Epislon Eridani 600 Myr 0.8M? K 3.2 pc 50 AU
Fomalhaut 200 Myr 2.1M? A 7.7 pc 133 AU
Epsilon Eridani
Greaves et al. 97
Staplefeldt et al.
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Discovery Space

• All extrasolar planets discovered by
  radial velocity (blue dots), transit (red) and
  microlensing (yellow) to 31 August 2004. Also
  shows detection limits of forthcoming space- and
  ground-based instruments.
• Discovery space for planet detections based on
  disk/planet interactions

More ambitiously in future
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Planets in disks

• Young systems, evolution of early solar systems
• Disk clearing by planets, Planet disk
  interactions
• Historical context for prediction of bodies prior
  to discovery
• Moonlet predicted in Enke gap from Voyager data
  (Cuzzi Scargle 85), body then detected
  Showalter 91
• Resonant ring in dust with Earth predicted
  (Jackson Zook 89) then seen in IRAS data
  (Dermott et al. 94)
• Neptunes location predicted by Adams LeVerrier
  (1845) then found by Galle (1846)

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Transition Disks

• Estimate of minimum planet mass to open a gap
  requires an estimate of disk viscosity.
• Disk viscosity estimate either based on clearing
  timescale or using study of accretion disks.
• Mp gt 0.1MJ

Wavelength µm
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Estimating required planet mass based on gap
opening criterion

• Limit on viscosity based on clearing during
  lifetime of object on a viscous timescale
• Or base on estimates for accretion disks

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Minimum Gap Opening Planet In an Accretion Disk
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CoKuTau4 is now known to be a binary star ? no
planet required
Kraus Ireland 08
Extremely empty clearing explained via binary

• Are planets no longer required to explain disk
  clearing in young stellar objects? NO
• Massive disks exist with clearings that could not
  have been cleared by photo-evaporation
  (Alexander, Najita Strom)
• Disks are seen in with large gaps, not just deep
  clearings as was CoKuTau4 --- these are best
  explained via planet formation and inefficient
  clearing

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Dust Capture models and Epsilon Eridani Debris
Disk

• Dust generated via collisions spirals inwards and
  is trapped in resonance with giant planets
• Dust source is late stage collisional evolution
  Debris Disks
• Dust rings as signposts of planets
• Liou Zook 99, Ozernoy et al. 01
• Vega disk model by Marc Kucher and collaborators
• Exploring eccentric planet space, Deller
  Maddison 05
• Rich History Earths resonant ring

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Capture of drifting dust by mean-motion
resonances with planets
Dust integration weighted by lifetime shows that
dust particles trapped in resonances dominate the
distribution
Signature of Giant planets seen in the
Edgeworth-Kuiper Belt (Liou Zook 1999)
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An early model for the dust ring in the Epsilon
Eridani system
Particles generated in resonance with an
eccentric planet Long resonance
lifetimes Different resonances contrived to make
clumps
Greaves et al.1997
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Epsilon Eridani Recent developments
Greaves et al.

• Not all clumps are real
• However clumps are rotating suggesting that there
  are some clumps in the disk in corotation with a
  planet
• Possible 1 or two inner planets in central AU
  from Radial velocity and proper motion scatter

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Multiple component dust models based on Spitzer
SED, imaging and IRS spectra
infrared excess model components
Backman et al. 09
2 inner asteroid belts and one outer one
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Update on planet scenarios for Epsilon Eridani

• Sticking planets right next to ring edges is
  moderately well justified
• Our model for outer planet is vastly out of date,
  eccentric planet no longer needed
• Collisions, migration, multiple planet
  interactions now key to understanding this system

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Lopsided disks, need for planets and the
Pericenter glow model
Fomalhaut

• Based on asymmetry in asteroid distribution due
  to Jupiters forced eccentricity
• Proposed to account for asymmetry of HR4796As
  disk (also has a clearing) by Mark Wyatt and
  collaborators
• Mass of planet is not constrained
• Eccentricity and semi-major of planet related but
  not individually constrained

Staplefeldt et al.
HR4796A nicmos
Schneider et al. 99
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• HST image hailed as another signpost of a
  planetary system but nature of system was poorly
  constrained

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Another model
Adam Deller and Sarah Maddisons resonant capture
model account for disk eccentricity but not sharp
edge collisions ignored
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Kalas et al. 05
Fomalhauts eccentric ring

• steep edge profile
• hz/r 0.013
• eccentric e0.11
• semi-major axis a133AU
• collision timescale 1000 orbits based on
  measured opacity at 24 microns
• age 200 Myr
• orbital period 1000yr

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Free and forced eccentricity
radii give you eccentricity If free eccentricity
is zero then the object has the same eccentricity
as the forced one ? longitude of pericenter
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Pericenter glow model

• Collisions cause orbits to be near closed ones.
  This implies the free eccentricities in the ring
  are small.
• The eccentricity of the ring is then the same as
  the forced eccentricity
• We require the edge of the disk to be truncated
  by the planet ?
• We consider models where eccentricity of ring and
  ring edge are both caused by the planet.
  Contrast with precessing ring models.

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Disk dynamical boundaries

• For spiral density waves to be driven into a disk
  
• (work by Espresate and Lissauer)
• Collision time must be shorter than libration
  time
• ? Spiral density waves are not efficiently driven
  by a planet into Fomalhauts disk
• A different dynamical boundary is required
• We consider accounting for the disk edge with the
  chaotic zone near corotation where there is a
  large change in dynamics
• We require the removal timescale in the zone to
  exceed the collisional timescale.

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Corotation chaotic zone

• Mean motion resonances get stronger and closer
  together near the planets corotation region.
• An object in the overlap region can make close
  approaches to the planet
• Width scales with planet mass to 2/7 power
  (Wisdom)

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Chaotic zone boundary and removal within
What mass planet will clear out objects inside
the chaos zone fast enough that collisions will
not fill it in? Mp gt Neptune
Neptune size
Saturn size
collisionless lifetime
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Dynamics at low free eccentricity

• Expand about the fixed point (the zero free
  eccentricity orbit)
• For particle eccentricity equal to the forced
  eccentricity and low free eccentricity, the
  corotation resonance cancels
• ? recover the 2/7 law, chaotic zone same width

goes to zero near the planet
same as for zero eccentricity planet
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Velocity dispersion in the disk edgeand an upper
limit on Planet mass

• Distance to disk edge set by width of chaos zone
• Last resonance that doesnt overlap the
  corotation zone affects velocity dispersion in
  the disk edge
• Mp lt Saturn

Larger masses also would leave structure in ring,
and it is featureless
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cleared out by perturbations from the planet Mp gt
Neptune
nearly closed orbits due to collisions eccentricit
y of ring equal to that of the planet
Assume that the edge of the ring is the boundary
of the chaotic zone. Planet cant be too massive
otherwise the edge of the ring would thicken or
show structure ? Mp lt Saturn
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• Neptune lt Mp lt Saturn
• Semi-major axis 119 AU (16 from star)
• location predicted using chaotic zone as
  boundary
• Eccentricity ep0.1, same as ring
• Longitude of periastron same as the ring

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Multiple Epoch HST imaging reveals an object
bound to the system
Planet discovered at 115AU Interpretation rests
on chaotic zone boundary
periapse
Kalas et al. 2008
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Surprises
Kalas et al 08

• Object is much much brighter than I predicted
• Planet itself is not detected.
• Object detected has colors of star and is 60
  times brighter in optical than a Jupiter mass
  planet
• IR observations rule out planets more massive
  than 3 Jupiters

• Circum-planetary disk to account for optical
  flux?
• Mass of planet is not known. Eugene Chiangs
  group suggest a larger planet than I predicted
• Planet is slightly further away from disk edge
  than predicted using chaotic zone boundary.
  Eccentricity of planet and planet disk
  interaction still yet to be explained.

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Summary
post discovery view

• 3 planets predicted
• CokuTau4 planet ruled out (but class of models
  still probably okay for other systems
• Epsilon Eridani outer planet model is missing
  key physics and so is out of date
• Fomalhaut. Planet location pretty closely
  predicted
• New models to create with multiple planets to
  interpret disks with large gaps (as inferred from
  their spectral energy distribution), including
  HR8799 and Epislon Eridani

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Nice Model Epoch of Late Heavy Bombardment

• Disk of Fomalhaut is cold, not what would be seen
  for Solar system during epoch of Late Heavy
  Bombardment
• Migration of planets in Fomalhaut system is likely

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Where is the next planet??