circumstellar disks: the formation and evolution of...

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Debris Disks and the Formation and Evolution of Planetary Systems…

Christine ChenOctober 14, 2010

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Outline

• Dust Debris in our Solar System• The Discovery of Dust Debris Around

Other Stars• The Connection Planet-Dust Connection• Unsolved Problems in Planetary System

Formation and Evolution• JWST and the Future of Debris Disk

Observations

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Outline




Observations

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Our Solar System

Terrestrial PlanetsAsteroid BeltJovian PlanetsKuiper BeltIce Dwarf PlanetsOort Cloud

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The Zodiacal Light

Mdust = 21020 g = 10-10 Mplanets = 10-4 MMABLIR(dust) = 100 LIR(planets)

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Asteroid Families

• In 1918 Hirayama discovered concentrations of asteroids in a-e-i space (osculatory orbital semi-major axis, eccentricity and inclination) he named “families”.

• It is widely believed that these families resulted from the break up of larger parent bodies.

Distribution of the proper sine of inclination vs. semi-major axis for the first 1500 numbered asteroids. The Hirayama families Themis (T), Eos (E), and Koronis (K) are marked. Kirkwood gaps are visible. The detached Phocaearegion is at upper left.Chapman et al. (1989)

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Origin of Dust Bands in the Zodiacal Light

• he , , dust bands in the Zodiacal Light are believed to have been generated by mutual collisions within the Themis, Koronis, and Eos families.

• Other dust bands are not found in association with other major asteroid families with the possible exception of the Io family.

• The Koronis family has a greater dust population than the larger Themisfamily.

• The majority of dust bands were probably produced by large random collisions among individual asteroids.

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The Kuiper Belt

More than one thousand km-sized KBOs have now been discovered. Although, no dusty disk has yet been detected, one is believed to exist.

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Outline




Observations

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The Vega Phenomenon• Routine calibration

observations of Vega revealed 60 and 100 μmfluxes 10 times brighter than expected from the stellar photosphere alone.

• Subsequent coronagraphicimages of Pic revealed an edge-on disk which extends beyond 1000 AU in radius.

• Infrared excess is well described by thermal emission from grains.

Backman & Paresce 1993

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A Circumstellar Disk Around Pictoris!

Mouillet et al. (1997)

Spectral Type: A5V

Distance: 19.3 pc

Tdust: 85 K

LIR/L*: 3 10-3

Mdust: 0.094 M

Rdust: 1400 AU

Inclination: 2-4º

Age: 20 ± 10 Myr

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Radiation Effects

Radiation Pressure

If Frad > Fgrav (or > 1), then small grain will be radiatively driven from the system

Artymowicz (1988)

tPR 4agrc

2D2

3L*

Poynting-Robertson Drag

Dust particles slowly spiral into the orbit center due to the Poynting-Robertson effect. The lifetime of grains in a circular orbit is given by

(Burns et al. 1979).

3L* Qpr (a) 16GM*ca

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Solar Wind Drag

The solar wind is a stream of protons, electrons, and heavier ions that are produced in the solar corona and stream off the sun at 400 km/sec

Typically, Fsw << Fgrav; therefore, stellar wind does not effectively drive dust out of the system radially.

However, they do produce a drag force completely analogous to the Poynting-Robertson effect

(Plavchan et al. 2005)

tsw 4agrD

2

3QswÝ M sw

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Debris Disks are dusty disks around main sequence stars. Unseen planets are believed to gravitationally perturb asteroids and comets, causing them to collide with one another generating fine dust grains. Astronomical telescopes detect the starlight scattered by these dust grains and the heat emitted from the grains.

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Outline




Observations

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A Possible Planet in the Pic Disk

STIS/CCD coronagraphic images of the Pic disk. The half-width of the occulted region is 15 AU. At the top is the disk at a logarithmic stretch. At bottom is the disk normalized to the maximum flux, with the vertical scale expanded by a factor of 4 (Heap et al. 2000)

Observed Dwarp = 70 AU48 MJup brown dwarf at <3 AU

Or17.4 MJup – 0.17 MJup planet at

5 – 150 AU

7/22 )( agePwarp taMD

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Direct Detection of Pic b

Pic

Standard Star HR 2435

Target/Standard

Target -Standard

Lagrange et al. 2008

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A Planet Around Fomalhaut…• The Fomalhaut disk’s

brightness asymmetry which may be caused by secular perturbations of dust grain orbits by a planet with a = 40 AU and e = 0.15

• Distance between planet and disk and thickness of disk suggest planet mass < 3MJup

Kalas et al. (2008)

(Stapelfeldt et al. 2005)

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• “Planet” is significantly brighter than expected at visual wavelengths• “Planet” possesses same color as center star• “Planet light” could be light scattered from circumplanetary dust grains that are

forming a moon

or a circumplanetary dust disk?

Kalas et al. 2008

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An Orbiting Planetary System Around HR 8799?

Marois et al. 2008 (see APOD: http://apod.nasa.gov/apod/ap081117.html):• Gemini North near-infrared (1.1 - 4.2 m) images• Reveal 3 objects with projected separations 24, 38, and 60 AU in nearly face-on orbit• Around HR 8799, an 160 Myr old, nearby (39.4 pc), main sequence A5V star

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• The SED of HR 8799 is best fit using two single temperature black bodies with temperatures, Tgr = 160 K and 40 K

• These temperatures correspond to distances of 8 AU and 110 AU, respectively.

An Asteroid Belt and a Kuiper Belt?

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Outline




Observations

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Outstanding Science Questions

• Do terrestrial planets form via the same mechanisms in other solar systems? – Are planetary embryos built up on the same timescales and via

the same processes?– Do large collisions occur, indicating possible moon forming events

or water delivery?

• Do the giant planets in other solar systems migrate, creating periods like the Late Heavy Bombardment?

• Is the Solar System’s composition and architecture (configuration of terrestrial planets, asteroid belt, Jovianplanets, and Kuiper Belt) common?

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Planet Formation in Our Solar System

• Once gas has dissipated, km-sized bodies agglomerate into oligarchs that stir small bodies

• Infrared observations of dust can help constrain disk properties during the period of oligarchic growth to determine average properties and magnitude of variation

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Terrestrial Planet Formation

Giant Planet Formation

1-3 Myr 10-30 MyrCore

FormationEnvelopeAccretion

~few Myr 30-100 Myr

Giant Impacts includingMoon Formation and

Late PatinaFormation of

km-sized bodies OligarchicGrowth

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Oligarchic Growth Simulations

• Coagulation N-body simulations (Kenyon & Bromley 2004, 2005, 2008)

• Gas dissipates on a timescale ~10 Myr

• Parent bodies with sizes 1m-1km at 30-150 AU in the disk

• Pluto-sized (1000 km) objects grow via collisions until gas dissipates

• They stir leftover planetesimals, which generates debris

26Chen et al. 2011

MIPS 24 m Excess Evolution• Our MIPS 24 m

observations of F0-F5 stars are broadly consistent with the Kenyon & Bromley (2008) models, but do not indicate a peak in the upper envelope of 24 m excess at 15-30 Myr

• The Carpenter et al. (2009) observation of US show that models must be updated to include dust within 30 AU around the late-type stars

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A Hypervelocity Collision Around HD 172555

• Silica (Tektite and Obsidian) and possible SiO gas detected

• Fine dust mass 1020 kg; gas mass 1022 kg, if gas is fluorescent

• If gas is dense then it must be transient

• High spectral resolution observations are needed to confirm SiO, measure gas properties and infer excitation mechanism

Lisse et al. 2009

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The Main Asteroid Belt as a Function of Time

• Simulations of the Main Asteroid Belt suggest that individual collisions between parent asteroids may have been detectable to outside observers

• Are debris disks observed today bright because they have undergone a recent collision?

Grogan et al. 2001

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The Period of Late Heavy Bombardment in Our Solar System

• The moon and terrestrial planets were resurfaced during a short period (20-200 Myr) of intense impact cratering 3.85 Gacalled the Late Heavy Bombardment (LHB)

• Apollo collected lunar impact melts suggest that the planetary impactorshad a composition similar to asteroids

• Size distribution of main belt asteroids is virtually identical to that inferred for lunar highlands

• Formation and subsequent migration of giant planets may have caused orbital instabilities of asteroids as gravitational resonances swept through the asteroid belt, scattering asteroids into the terrestrial planets.

Strom et al. (2005)

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Is Crv Experiencing a Period of Late Heavy Bombardment?

• The SED shows warm (~300 K) and cool components (~30 K)• The mid-infrared spectrum of the warm component is well modeled

using primitive materials such as amorphous silicates and carbon, metal sufides, and water ice

Wyatt et al. 2004 Lisse et al. 2011

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Outline




Observations

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JWST MIRI

• 6.5 m primary mirror• Direct imaging: 5.6-25.5 m• Coronagraphic Imaging:

– 4QPM 10.65, 12.3, 15.5 m– Lyot 23 m

• Low Resolution Spectrograph (R~100): 5-10 (14) m

• Medium Resolution Spectrograph (R~3000): 5-27 m

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Mid-Infrared Imaging of the Vega Disk

• Spitzer MIPS 24 and 70 m imaging has revealed a large extended disk at distances > 85 away from the central star

• The dust geometry and the low apparent vsini of the star suggests that the star-disk system is face-on

• Mid-infrared imaging is sensitive to smallest grains that are eithergravitationally unbound or on eccentric orbits

Su et al. 2005

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Millimeter Imaging of the Vega Disk

• IRAM Plateau de Bure inteferometric observations at 1.3 mm detected dust in two lobes around Vega, at distances 9.5 and 8.0from the central star

• The observations can be explain using large dust grains that aretrapped into principal mean motion resonances of a 3 MJup planet

Wilner et al. 2002

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High Resolution Multi-wavelength Imaging

• Sub-blow out sized dust grains will be subject to radiation pressure(infrared imaging)

• Largest grains may be trapped in resonances (submm/mm imaging)• Intermediate-sized grains may be at similar distances as larger

grains but not physically trapped in resonances (far-infrared imaging)

Wyatt 2006

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Processed Grains in the Outer Solar System

• Infrared spectroscopy of comets and analysis of comet dust grains from STARDUST suggest that comets possess crystalline silicates

• How does material processed at high temperatures near the sun mix in a proto-planetary disk become incorporated into cold bodies such as comets?

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Spatially Resolved Spectroscopy

• Gradients in grain size as a function of position in debris disks may suggest the presence of planetesimal belts (e.g. Okamoto et al. 2004 - Pic)

• Gradients in grain composition as a function of position may allow use to test theories for the origin of atomic gas

Okamoto et al. 2004

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Conclusions

• Our Solar System possesses second generation dust generated by sublimation of comets and collisions between asteroids and KBOs

• There are exoplanetary systems that possess similar dust• In these systems, collisions between asteroids and comets is

believed to generate dust• Whenever disks are observed at high angular resolution,

structures, suggesting the presence of planets are discovered

• Observations of these systems can help us place constraints on terrestrial planet formation and solar system evolution

• JWST is expected to make important contributions to our understanding of debris disks

circumstellar disks: the formation and evolution of...

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