Transcript Circumstellar Disks: the Formation and Evolution of

Debris Disks and the Formation and
Evolution of Planetary Systems…
Christine Chen
October 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
• 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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Our Solar System
Terrestrial Planets
Asteroid Belt
Jovian Planets
Kuiper Belt
Ice Dwarf Planets
Oort Cloud
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The Zodiacal Light
Mdust = 21020 g = 10-10 Mplanets = 10-4 MMAB
LIR(dust) = 100 LIR(planets)
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Asteroid Families
Distribution of the
proper sine of
inclination vs. semimajor 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 Phocaea
region is at upper left.
Chapman et al.
(1989)
•
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.
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Origin of Dust Bands in the Zodiacal Light
•
The a, b, g 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 Themis
family.
•
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
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is believed to exist.
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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The Vega Phenomenon
• Routine calibration
observations of Vega
revealed 60 and 100 μm
fluxes 10 times brighter
than expected from the
stellar photosphere alone.
• Subsequent coronagraphic
images of b Pic revealed
an edge-on disk which
extends beyond 1000 AU in
radius.
• Infrared excess is well
described by thermal
emission from grains. 10
Backman & Paresce 1993
A Circumstellar Disk Around b Pictoris!
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
Mouillet et al. (1997)
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Radiation Effects
Poynting-Robertson Drag
Radiation Pressure
If Frad > Fgrav (or b > 1), then small
grain will be radiatively driven
from the system
3L*  Qpr (a) 
b
16GM*ca
Artymowicz (1988)
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
t PR
4 agrc 2 D2

3L*
(Burns et al. 1979).
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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 PoyntingRobertson effect
4agr D2
tsw 
Ýsw
3Qsw M
(Plavchan et al. 2005)
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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
• 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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A Possible Planet in the b Pic Disk
Dwarp  (M P a2tage )2 / 7
Observed Dwarp = 70 AU
48 MJup brown dwarf at <3 AU
Or
17.4 MJup – 0.17 MJup planet at
5 – 150 AU
STIS/CCD coronagraphic images of the b 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 16
expanded by a factor of 4 (Heap et al. 2000)
Direct Detection of b Pic b
Standard
Star
HR 2435
b Pic
Target/
Standard
Target Standard
Lagrange et al. 2008 17
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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or a circumplanetary dust disk?
Kalas et al. 2008
•
•
•
“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
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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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An Asteroid Belt and a Kuiper Belt?
• 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
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and 110 AU, respectively.
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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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, Jovian
planets, and Kuiper Belt) common?
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Planet Formation in Our Solar System
Terrestrial Planet Formation
Formation of
km-sized bodies Oligarchic
Growth
~few Myr
Giant Impacts including
Moon Formation and
Late Patina
30-100 Myr
time
1-3 Myr
Core
Formation
10-30 Myr
Envelope
Accretion
Giant Planet Formation
•
•
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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Oligarchic Growth Simulations
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•
•
•
•
Coagulation N-body simulations
(Kenyon & Bromley 2004, 2005,
2008)
Gas dissipates on a timescale
~10 Myr
Parent bodies with sizes 1m1km 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
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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 latetype stars
Chen et al. 2011
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A Hypervelocity Collision Around HD 172555
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•
•
•
Lisse et al. 2009
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
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The Main Asteroid Belt as a Function of Time
Grogan et al. 2001
• 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?
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The Period of Late Heavy Bombardment in Our
Solar System
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The moon and terrestrial planets were
resurfaced during a short period (20-200
Myr) of intense impact cratering 3.85 Ga
called the Late Heavy Bombardment
(LHB)
•
Apollo collected lunar impact melts
suggest that the planetary impactors
had 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?
Wyatt et al. 2004
Lisse et al. 2011
• 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,
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metal sufides, and water ice
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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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
Su et al. 2005
• 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 either
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gravitationally unbound or on eccentric orbits
Millimeter Imaging of the Vega Disk
Wilner et al. 2002
• IRAM Plateau de Bure inteferometric observations at 1.3 mm
detected dust in two lobes around Vega, at distances 9.5 and 8.0
from the central star
• The observations can be explain using large dust grains that are
trapped into principal mean motion resonances of a 3 MJup planet 34
High Resolution Multi-wavelength Imaging
Wyatt 2006
• 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)
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Processed Grains in the Outer Solar System
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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
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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 - b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
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