Understanding the extrasolar planetary systems: observations & theories of disks and planets
Pawel Artymowicz U of Toronto
1. Beta Pictoris and other dusty disks in planetary systems2. Planet formation: are there really still two scenarios?3. Discovery of the first 160+ planetary systems4. Migration type I-III5. Origin of structure in the dust and gas disksHow to find this talk online: either google up “pawel”, or get directly
planets.utsc.utoronto.ca/~pawel/UofA.ppt
Gen.Rel.
Radiation transfer
Thermodynamics of gas
StellarAstrophysics
Disk
theo
ry
Astrophysicsof planetarysystems
Astronomy:observationsof circumstellar disks
Dynamics incl.Hydrodynamicsand statics
Nuclearphysics
High energphysics.
meteoritics
IDPs & zodiacal disk
radioisotopes
materials
atmosph.
Geo-chem
Gen.Rel.
Radiation transfer
Thermodynamics of gas
StellarAstrophysics
Astrophysicsof planetarysystems
Astronomy:observationsof circumstellar disks, radial velocity exoplanets
Dynamics,hydrodynamicsand hydrostatics
Nuclearphysics
High ener.physics.
meteoritics
radioisotopes
materials
atmosph.
Geo-chem
Disk th
eory
IDPs, zodiacal light disks
First milestone in search for planetary systems was detection of dust around normal stars :
Vega phenomenon
Chemistry/mineralogy/crystallinity of dust
Astrochemical unity of nature
Infrared excess stars (Vega phenomenon)
Beta Pictoris thermal radiation imaging (10 um)Lagage & Pantin (1993)
1984
1993Beta Pictoris, visible scattered starlightcomparison with IR data yields a high albedo, A~0.4-0.5(like Saturn’s rings but very much unlike the black particles ofcometary crust or Uranus’ rings).
Small dust is observed due to its large total area
Parent bodies like these (asteroids, comets) are the ultimate sources ofthe dust, but remain invisible in images due to their small combinedarea
Comet
Optical thickness:
perpendicular to the disk
in the equatorial plane (percentage of starlight scattered and absorbed, as seen by the outside observer looking at the disk edge-on, aproximately like we look through the beta Pictoris disk)
)(
)(
r
r
eq
What is the optical thickness ?
It is the fraction of the disk surface covered by dust:here I this example it’s about 2e-1 (20%) - the disk is optically thin ( = transparent, since it blocks only 20% of light)
picture of a small portion of the disk seen from above
Examples: beta Pic disk at r=100 AU opt.thickness~3e-3 disk around Vega opt.thickness~1e-4
zodiacal light disk (IDPs) solar system ~1e-7
)(r
Vertical optical thickness
Vertical profile ofdust density
Radius r [AU] Height z [AU]
STIS/Hubble imaging (Heap et al 2000)
Modeling (Artymowicz,unpubl.):parametric, axisymmetric diskcometary dust phase function
Dust processing: collisions
1. Collisional time formula
2. The analogy with the early solar system(in the region of today’s TNOs = trans-Neptunian objects, or in other words,Kuiper belt objects, KBOs; these are asteroid-sizedbodies up to several hundred km radius)
collt Time between collisions (collisional lifetime) of a typical meteoroid. Obviously, inversly proportional to the optical thickness (doubling the optical depth results in 2-times shorter particle lifetime, because the rate of collisiondoubles).
)/( 8Ptcoll
P = orbital period, depends on radius as in Kepler’s III law.
This formula is written with a numerical coefficion of 1/8 so as to reproduce the fact that a disk made of equal-sized particles needs tohave the optical thickness of about 1/4 to make every particle traversing it vertically collide with some disk particle, on average. The vertical piercing of the disk is done every one-half period, because particles are on inclined orbits and do indeed cross the disk nearly vertically, if on circular orbits. If the orbits are elliptic, a better approximate formula has a coefficient of 12 replacing 8 in the aboveequation.
How does the Vega-phenomenon relate to our Solar System(Kuiper belt, or TNOs - transneptunian objects)
Evidence of planetesimals and planetsin the vicinity of beta Pictoris:
1. Lack of dust near the star (r<30AU)2. Spectroscopy => Falling Evaporating Bodies3. Something large (a planet) needed to perturb FEBs so they approach the star gradually. 4. The disk is warped somewhat, like a rim of cowboy hat, which requires the gravitational pull of a planet on an orbit inclined by a few degrees to the plane of the disk.5. Large reservoir of parent (unseen) bodies of dust needed, of order 100 Earth masses of rock/ice. Otherwise the dust would disappear quickly, on the collisional time scale
This is how disks look a decade later - much better quality data, fewerartifacts, disks appear smoother.
HST/WFPC2 camera
a fantastic large-scale view of beta Pictorisout to r ~800 AU
Beta Pictoris
11 micron image analysis converting observed fluxto dust area (Lagage & Pantin 1994)
B Pic b(?) sky?
Evidence of large bodies (planetesimals, comets?)
FEB = Falling Evaporating Bodies hypothesis in Beta Pictoris
absorption line(s) thatmove on the time scale of days as the FEBs cross the line of sight
H & K calcium absorption linesare located in the center of a stellar rotation-broadened line
FEB
star
Microstructure of circumstellardisks: identical with IDPs(interplanetary dust particles)
mostly Fe+Mg silicates(Mg,Fe)SiO3
(Mg,Fe)2SiO4
A rock is a rock is a rock…
which one isfrom the Earth?
Mars?
Beta Pic?
It’s hard to tell from remote spectroscopy or even by looking under a microscope!
What minerals will precipitate from asolar-composition,cooling gas? Mainly Mg/Fe-rich silicates and water ice. Planets are made of precisely these things.
Silicatessilicates
ices
T(K)
Chemical unityof nature… and it’sthanks to stellar nucleosynthesis!
EQUILIBRIUM COOLING SEQUENCE
Crystallinity of minerals
Recently, for the first time observations showed the differencein the degree of crystallinity of minerals in the inner vs. the outer diskparts. This was done by comparing IR spectra obtained with single dishtelescopes with those obtained while combining several such telescopesinto an interferometric array (this technique, long practiced by radioastronomers, allows us to achieve very good, low-angular resolution,observations).
In the following 2 slides, you will see some “inner” and “outer” disk spectra - notice the differences, telling us about the differentstructure of materials:
amorphous silicates = typical dust grains precipitating from gas,for instance in the interstellar medium, no regular crystal structure
crystalline grains= same chemical composition, but forming a regular crystal structure, thought to be derived from amorphous grains bysome heating (annealing) effect at temperatures up to ~1000 K.
~90% amorphous
~95% crystalline
~45% amorphous
com
pare
~60% amorphous
Beta Pic,
That was good, but people wanted PLANETS
Structuresin dusty disks(footprintsin the sand)
Indirect butalmost direct: periodic, Keplerian red+blueshiftsin stellar spectra,or timing of pulsars
Direct imaging
Transits
Pulsar planets: PSR 1257+12 B2 Earth-mass planets and one Moon-sizes onefound around a millisecond pulsar
First extrasolar planets discovered by Alex Wolszczan [pron.: Volshchan] in 1991, announced 1992, confirmed 1994
Name: PSR 1257+12 A PSR 1257+12 B PSR 1257+12 C M.sin 0.020 ± 0.002 ME 4.3 ± 0.2 ME 3.9 ± 0.2 ME
Semi-major axis: 0.19 AU 0.36 AU 0.46 AU
P(days): 25.262±0.003, 66.5419± 0.0001, 98.2114±0.0002
Eccentricity: 0.0 0.0186 ± 0.0002 0.0252 ± 0.0002
Omega (deg): 0.0 250.4 ± 6 108.3 ± 5
The pulsar timing is so exact, observers now suspect having detected a comet!
Pulsar planets: PSR 1257+12 B2 Earth-mass planets and one Moon-sizes onefound around a millisecond pulsar
A B C
m: 0.020 ME 4.3 ME 3.9 ME
a: 0.19 AU 0.36 AU 0.46AU
e: 0 0.0186 0.0252
O: 0.0 250.4 108.3
First extrasolar planets discovered by Alex Wolszczan [pron.: Volshchan] in 1991, announced 1992, confirmed 1994
+comets ??
Radial-velocity planets
around normal stars
-450: Extrasolar systems predicted (Leukippos, Demokritos). Formation in disks-325 Disproved by Aristoteles
1983: First dusty disks in exoplanetary systems discovered by IRAS
1992: First exoplanets found around a millisecond pulsar (Wolszczan & Dale)
1995: Radial Velocity Planets were found around normal, nearby stars,via the Doppler spectroscopy of the host starlight, starting with Mayor & Queloz, continuing wth Marcy & Butler, et al.
Orbital radii + masses of the extrasolar planets (picture from 2003)
These planets were foundvia Doppler spectroscopyof the host’s starlight.
Precision of measurement:~3 m/s
Hot jupitersRadial migration
Like us? NOT REALLY
Marcy and Butler (2003)
~2003
2005
m sin i vs. aZones ofavoidance?
multiple
single
m sin i vs. aZones ofavoidance?
Result: a----m
Eccentricity of exoplanets vs. a and m sini
m, a, e somewhat correlated: a e ? m
a e ? m
a e ? m
Eccentricity of exoplanets vs. a and m sini
m, a, e somewhat correlated: a e ? m
a e ? m
a e ? m
Gravitational Instabilityand the Giant GaseousProtoplanet hypothesis
Gravitational stability requirements
1
1
Q
Q
numberToomreSafronovGc
Q
Local stability of disk, spiral waves may grow
Local linear instability of waves, clumps form,
but their further evolution depends on equation of
state of the gas.
From: Laughlin & Bodenheimer (2001)
Disk in this SPH simulationinitially had Q ~ 1.5 > 1
The m-armed global spiral modes of the form
grow and compete with each other.
But the waves in a stableQ~2 disk stop growing and do not form small objects (GGPs).
)](exp[ tdrkmi
Clumps forming in a gravitationallyunstable disk
(Q < 1)
Recently, Alan Boss revived the half-abandoned idea of disk fragmentation
GGPs?
Two examples of formally unstable disks not willing to form
objects immediately Durisen et al. (2003)
Break-up of the disk depends on the equation of state of the gas,and the treatment of boundary conditions.
Simulations of self-gravitating objects forming in the disk (with grid-based hydrodynamics) shows that rapid thermal cooling is crucial
Armitage and Rice (2003)
Disk not allowedto cool rapidly (cooling timescale > 1 P)
Disk allowedto cool rapidly(on dynamical timescale, <0.5 P)
SPH = SmoothedParticle Hydrodynamics
with 1 millionparticles
Mayer, Quinn, Wadsley, Stadel (2003)
Isothermal(infinitely rapid cooling)
GGP (Giant Gaseous Protoplanet) hypothesis= disk fragmentation scenario (A. Cameron in the 1970s)
Main Advantages: forms giant planets quickly, avoids possible timescale paradox; planets tend to form at large distances amenable to imaging.
MAIN DIFFICULTIES:1. Non-axisymmetric and/or non-local spiral modes start developing not only at Q<1 but already when Q decreases to Q~1.5…2 They redistribute mass and heat the disk => increase Q (stabilize disk).
2. Empirically, this self-regulation of the effects of gravity on disk is seenin disk galaxies, all of which have Q~2 and yet don’t split into many baby gallaxies.
3. The only way to force the disk fragmentation is to lower Q~c/Sigma by a factor of 2 in just one orbital period. This seems impossible.
4. Any clumps in disk (e.g. A. Boss’ clumps) may in fact shear and disappearrather than form bound objects. Durisen et al. Have found that the equation of state and the correct treatment of boundary conditions are crucial, but couldnot confirm the fragmentation except in the isothermal E.O.S. case.
5. GGP is difficult to apply to Uranus and Neptune; final masses: Brown Dwarfs not GGPs
6. Does not easily explain core masses of planets and exoplanets, nor the chemical correlations (to be discussed in lecture L23)
Video of density waves in a massive protoplanetary diskThe shocks at the surface are suggested as a way to heat solidsand form chondrules, small round grains inside meteorites.
Durisen and Boss (2005)
Envelope instability in proto-giants
(nucleated gas accretion)
Comparison of gas and rock masses (in ME)
in giant planets and exoplanets (1980s)
Planet Core mass Atmosph. Total mass Radius _________(rocks, ME )___(gas,_ME )____(ME )_______(RJ) _
Jupiter 0-10 ~313 318 1.00 Saturn 15-20 ~77 95 0.84 Uranus 11-13 2 - 4 14.6 0.36 Neptune 13-15 2 - 4 17.2 0.34
core envelope (atmosphere)
Comparison of gas and rock masses (in ME)
in giant planets and exoplanets (Oct. 2005)
Planet Core mass Atmosph. Total mass Radius _________(rocks, ME )___(gas,_ME )____(ME )_______(RJ) _
Jupiter 0-10 ~313 318 1.00 Saturn 15-20 ~77 95 0.84 Uranus 11-13 2 - 4 14.6 0.36 Neptune 13-15 2 - 4 17.2 0.34
HD 209458b ~0 ~220 204-235 1.32 ± 0.05 (disc. 1999)
HD 149026b ~70 ~45 105-124 0.73 ± 0.03 (disc. 7/2005)
HD 189733b ~10-20(?) ~350 351-380 1.26 ± 0.03 (disc. 10/2005)
core envelope (atmosphere)
?
?
Standard Accumulation Scenario
Two-stage accumulation of planets in disks
Mcore=10 ME(?) =>contraction of theatmosphere and inflowof gas from the disk
Planetesimal = solidbody >1 km
(issues not addressedin the standard theoryso far)
How many planetesimals formed in the solar nebula?
Core-atmosphere instability above a critical core massMizuno (1980), Bodenheimer (1980s), Stevenson (1986)
Planetesimals supply heat of accretion L = GM/Rc (dM/dt)
Convection and radiation carry that luminosity away as dictated by equations of stellar stucture.
Low-mass cores have tenuous hydrogen-helium dominated envelopes that smoothly join the surrounding disk.
Opacity of the atmosphere and L have a major influence onthe envelope mass. When Mcore = Matm, the hydrostatic equations of stellar structure no longer have solutions.
The critical core mass (above which no equilibrium is possible) depends on opacity K and luminosity L as
Mcrit ~ (K L)^(- 3/4)
Mcrit ~ 8-20 ME in our solar system, perhaps different in others
Upsilon Andromedae
And the question of planet-planet vs. disk planet interaction
The case of Upsilon And examined: Stable or unstable? Resonant? How, why?...
Upsilon Andromedae’s two outer giant planets have STRONG interactions
Innersolarsystem(samescale)
.
1
2Definition of logitude of pericenter (periapsis) a.k.a.misalignment angle
In the secular pertubation theory, semi-major axes (energies) are constant (as a result of averaging over time).
Eccentricities and orbit misalignment vary, such asto conserve the angular momentum and energy of the system.
We will show sets of thin theoretical curves for (e2, dw).[There are corresponding (e3, dw) curves, as well.]
Thick lines are numerically computed full N-body trajectories.
Classical celestial mechanics
ecce
ntr
icit
y
Orbit alignment angle
0.8 Gyr integration of 2 planetary orbitswith 7th-8th order Runge-Kutta method
Initial conditionsnot those observed!
Upsilon And: The case of very good alignment of periapses: orbital elements practically unchanged for 2.18 Gyr
unchanged
unchanged
N-body (planet-planet) or disk-planet interaction?Conclusions from modeling Ups And
1. Secular perturbation theory and numerical calculations spanning 2 Gyr in agreement.2. The apsidal “resonance” (co-evolution) is expectedand observed to be strong, and stabilizes the systemof two nearby, massive planets3. There are no mean motion resonances4. The present state lasted since formation period5. Eccentricities in inverse relation to masses, contrary to normal N-body trend tendency for equipartition.Alternative: a lost most massive planet - very unlikely6. Origin still studied, Lin et al. Developed first modelsinvolving time-dependent axisymmetric disk potential
Diversity of exoplanetary systems likely a result of: cores?
disk-planet interaction a m e (only medium) yes
planet-planet interaction a m? e yes
star-planet interaction a m e? yes
disk breakup (fragmentation into GGP) a m e? Metallicity no
X
XX X
X X
X
X
:
resonances and wavesin disks, orbital evolution
Disk-planet interaction
This part of the lecture is more advanced andoptional (not required for the exam, for instance)If you are skipping it, please go directly to the last slide.
.
.
.
SPH (Smoothed Particle Hydrodynamics)Jupiter in a solar nebula (z/r=0.02) launches waves at LRs. The two views are (left) Cartesian, and (right) polar coordinates.
Inner and Outer Lindblad resonances in an SPH disk with a jupiter
Illustration of nominal positions of Lindblad resonances (obtained by WKB approximation. The nominal positions coincide with the mean motion resonances of the type m:(m+-1) in celestial mechanics, which doesn’t include pressure.) Nominal radii converge toward the planet’s semi-major axis at high azimuthal numbers m, causing problems with torque calculation (infinities!).
On the other hand, the pressure-shifted positions are the effective LR positions, shown by the green arrows. They yield finite total LR torque.
Wave excitation at Lindblad resonances (roughly speaking,places in disk in mean motion resonance, or commensurabilityof periods, with the perturbing planet) is the basis of the calculation of torques (and energy transfer) between the perturber and the disk. Finding precise locations of LRs isthus a prerequisite for computing the orbital evolution of a satellite or planet interacting with a disk.
LR locations can be found by setting radial wave numberk_r = 0 in dispersion relation of small-amplitude, m-armed, waves in a disk. [Wave vector has radial component k_r and azimuthal component k_theta = m/r]
This location corresponds to a boundary between the wavy andthe evanescent regions of a disk. Radial wavelength, 2*pi/k_r, becomes formally infinite at LR.
--> m(z/r)Ecc
entr
icit
y pu
mpi
ng
Eccentricity in type-Isituation is always strongly damped.
Conclusion about eccentricity:
As long as there is some gas in the corotational region(say, +- 20% of orbital radius of a jupiter), eccentricity is strongly damped.
Only if and when the gap becomes so wide that thenear-lying LRs are eliminated, eccentricity is excited.(==> planets larger than 10 m_jup were predicted to be on eccentric orbits (Artymowicz 1992).
In practice, this may account for intermediate-e exoplanets.
For extremely high e’s we need N-body explanation:perturbations by stars, or other planets.
Disk-planet interaction:
numerics
Mass flows through the gapopened by a jupiter-class exoplanet
==> Superplanets can form
Mass flows despitethe gap. This resultexplains the possibility of “superplanets” with mass ~10 MJ
Migration explains hot jupiters.
Binary star on circular orbitaccreting from a circumbinary disk through a gap.
Surface density Log(surface density)
An example of modern Godunov (Riemann solver) code:PPM VH1-PA. Mass flows through a wide and deep gap!
AMR PPM (Flash) simulation of a Jupiter in a standard solar nebula. 5 levels/subgrids.(P
epli
nski
an d
Ar t
y mow
icz
2 004
)
What does the permeability of gaps teach us about our own Jupiter:
- Jupiter was potentially able to grow to 5-10 mj, if left accreting from a standard solar nebula for ~1 Myr
- the most likely reason why it didn’t: the nebula was already disappearing and not enough mass was available.
Variable-resolutionPPM (Piecewise Parabolic Method)[Artymowicz 1999]
Jupiter-mass planet,fixed orbit a=1, e=0.
White oval = Roche lobe, radius r_L= 0.07
Corotational region outto x_CR = 0.17 from the planet
disk
disk gap (CR region)
Outward migration type IIIof a Jupiter
Inviscid disk with an inner clearing & peak density of 3 x MMSN
Variable-resolution,adaptive grid (following the planet). Lagrangian PPM.
Horizontal axis showsradius in the range (0.5-5) a
Full range of azimuthson the vertical axis.
Time in units of initialorbital period.
How can there be ANY SURVIVORS of the rapid type-III migration?!
Migration type III Structure in the disk:gradients od density,
edges, gaps, dead zones
Migration stops,planet grows/survives
Edges or gradients in disks:
Magneticcavities aroundthe star
Dead zones
Unsolved problem of the Last Mohican scenario of planet survival in the solar system:Can the terrestial zone survive a passage of a giant planet?
N-body simulations, N~1000 (Edgar & Artymowicz 2004)
A quiet disk of sub-Earth mass bodies reacts to the rapid passage of a much larger protoplanet (migration speed = input parameter).
Results show increase of velocity dispersion/inclinations and limited reshuffling of material in the terrestrial zone.
Migration type III too fast to trap bodies in mean-motion resonances and push them toward the star
Evidence of the passage can be obliterated by gas drag on the time scale << Myr ---> passage of a pre-jupiter planet(s) not exluded dynamically.
1. Early dispersal of the primordial nebula ==> no material, no mobility2. Late formation (including Last Mohican scenario)
Origin of structure in dusty disks:
Source: P. Kalas
HD107146
Disk of Alpha PiscesAustrini(a PsA)= Fomalhaut
a bright southern startype A
A new edge-on disk!
NICMOS/HST
(Schneideret al 2005)
near-IR band(scattered light)
This is how disks look when justdiscovered
HD 141569A is a Herbig emission star>2 x solar mass, >10 x solar luminosity, hydrogen emission lines H are double, because they come from a rotating inner gas disk. CO gas has also been found at r = 90 AU. Observations by Hubble Space Telescope (NICMOS near-IR camera).
Age ~ 5 Myr, a transitional disk
Gap-opening PLANET ?So far out??
TYPE III MIGRATION?
R_gap ~350AUdR ~ 0.1 R_gap
HD 14169A disk gap confirmed by new observations (HST/ACS)
Summary of the various effects of radiation pressure of starlight on dust grains in disks:
alpha particles = stable, orbiting particles on circular & elliptic orbits
beta meteoroids = particles on hyperbolic orbits,escaping due to a large radiationpressure
Radiation pressure coefficient (radiation pressure/gravity force)of an Mg-rich pyroxene mineral, as a function of grain radius s.
50.
sm / 2
s
Above a certain beta value, a newly created dust particle,released on a circular orbit of its large parent body (beta=0)will escape to infinity along the parabolic orbit.
What is the value of beta guaranteeing escape?It’s 0.5 (see problem 1 from set #5).
We call the physical radius of the particle that has thiscritical beta parameter a blow-out radius of grains.
From the previous slide we see that in the beta Pictoris disk, the blow-out radius is equal ~2 micrometers.Observations of scattered light, independent of this reasoning show that, indeed, the smallest size of observed grains is s~2 microns. Particles larger but not much larger than this limit will stay in the disk on rather eccentric orbit.
How radiation pressure induces large eccentricity:
= Frad / Fgrav
Radiative blow-out of grains (-meteoroids, gamma meteoroids)
Dust avalanches
Radiation pressure on dust grains in disks
Neutral (grey)scattering from s> grains
Repels ISM dust Disks = Nature, not nurture!
Enhanced erosion;shortened dust lifetime
Orbits of stable -meteoroids elliptical
Dust migrates,forms axisymmetric rings, gaps
(in disks with gas)
Short disk lifetime
Size spectrum of dust has lower cutoff
Weak/no PAH emission
Quasi-spiral structure
Instabilities (in disks)1
Age paradox
Coloreffects
Structure formation in dusty disks
The danger of overinterpretation of structure
Are the PLANETS responsible for EVERYTHING we see? Are they in EVERY system?
Or are they like the Ptolemy’s epicycles, added each time we need to explain a new observation?
FEATURES in disks: (9 types)
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN: (10 categories)
■ instrumental artifacts, variable PSF, noise, deconvolution etc.■ background/foreground obj.■ planets (gravity)■ stellar companions, flybys■ dust migration in gas■ dust blowout, avalanches■ episodic release of dust■ ISM (interstellar wind)■ stellar UV, wind, magnetism■ collective effects (radiation in opaque media, selfgravity)
(Most features additionally depend onthe viewing angle)
AB Aur : disk or no disk?
Fukugawa et al. (2004)
another “Pleiades”-type star
no disk
Source: P. Kalas
?
Hubble Space Telescope/ NICMOS infrared camera
FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ planets (gravity)
.
Some models of structure in dusty disks rely on too limited a physics: ideally one needs to follow: full spatial distribution, velocity distribution, and size distribution of a collisional system subject to various external forces like radiation and gas drag -- that’s very tough to do! Resultant planet depends on all this.
Beta = 0.01(monodisp.)
Dangers of fittingplanets to individual frames/observations:
Vega has 0, 1, or 2 blobs, depending on bandpass. What about its planets?Are they wavelength-
dependent too!?850 microns
HD 141569A is a Herbig emission star>2 x solar mass, >10 x solar luminosity,Emission lines of H are double, because they come from a rotating inner gas disk. CO gas has also been found at r = 90 AU. Observations by Hubble Space Telescope (NICMOS near-IR camera).
Age ~ 5 Myr, a transitional disk
Gap-opening PLANET ?So far out?? R_gap ~350AU
dR ~ 0.1 R_gap
Outward migration of protoplanets to ~100AUoroutward migration of dust to form rings and spirals
may be required to explain the structure in transitional (5-10 Myr old) and older dust disks
HD141569+BC in V band HD141569A deprojected
HST/ACS Clampin et al.
FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ stellar companions, flybys
Beta = 4H/r = 0.1Mgas = 50 ME
Best model, Ardila et al (2005)involved a stellar fly-by &
HD 141569A
5 MJ, e=0.6, a=100 AUplanet
FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ dust migration in gas
In the protoplanetary disks (tau) dust follows gas.Sharp features due to associatedcompanions: stars, brown dwarfs and planets.
These optically thin transitional disks (tau <1) must have some gas even if it's hard to detect.
Warning: Dust starts to move w.r.t. gas!Look for outer rings, inner rings, gapswith or without planets.
These replenished dust diskare optically thin (tau<<1)and have very little gas.
Sub-planetary & planetary bodies can be detected via spectroscopy,spatial distribution of dust, but do not normally expect sharp features.
Extensive modeling including dust-dust collisions and radiation pressure needed
Planetary systems: stages of decreasing dustiness
Pictoris
1 Myr
5 Myr
12-20 Myr
Gas pressure force
Gas pressure force
vgv=vK
v vg
Migration:
Type 0Dusty disks: structure
from gas-dust coupling (Takeuchi & Artymowicz 2001)
theory will help determine gas distribution
Gas disk tapersoff here
Predicted dust distribution: axisymmetric ring
Radiative blow-out of grains (-meteoroids, gamma meteoroids)
Dust avalanches
Radiation pressure on dust grains in disks
Neutral (grey)scattering from s> grains
Repels ISM dust Disks = Nature, not nurture!
Enhanced erosion;shortened dust lifetime
Orbits of stable -meteoroids elliptical
Dust migrates,forms axisymmetric rings, gaps
(in disks with gas)
Short disk lifetime
Size spectrum of dust has lower cutoff
Weak/no PAH emission
Quasi-spiral structure
Instabilities (in disks)1
Age paradox
Coloreffects
Dust avalanches and implications:
-- upper limit on dustiness-- the division of disks into gas-rich, transitional and gas-poor
FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ dust blowout avalanches,■ episodic/local dust release
Radiative blow-out of grains (-meteoroids, gamma meteoroids)
Dust avalanches
Radiation pressure on dust grains in disks
Neutral (grey)scattering from s> grains
Repels ISM dust Disks = Nature, not nurture!
Enhanced erosion;shortened dust lifetime
Orbits of stable -meteoroids elliptical
Dust migrates,forms axisymmetric rings, gaps
(in disks with gas)
Short disk lifetime
Size spectrum of dust has lower cutoff
Weak/no PAH emission
Quasi-spiral structure
Instabilities (in disks)1
Age paradox
Coloreffects
Limit on firin gas-free disks
Dust Avalanche (Artymowicz 1997)
= disk particle, alpha meteoroid ( < 0.5)
= sub-blowout debris, beta meteoroid ( > 0.5)
Process powered by the energy of stellar radiation N ~ exp (optical thickness of the disk * <#debris/collision>)
N
The above example is relevant to HD141569A, a prototype transitional disk (with interesting quasi-spiral structure.) Conclusion:
60
2
1
2
10~)20exp(~)exp(/
10~
2.0018.0)1.0(
)/(
)2/()/()/(
)2/()4/(2
NNN
NNdN
N
fzr
so
rdrzrdrs
rdrrrdrf
IR
IR
Transitional disks MUST CONTAIN GAS or face self-destruction.Beta Pic is almost the most dusty, gas-poor disk, possible.
the midplane optical thickness
Ratio of the infrared luminosity (IR excess radiation from dust) to the stellar luminosity; it gives the percentage of stellar flux absorbed reemitted thermally
multiplication factor of debris in 1 collision (number of sub-blowout debris)
Avalanche growth equation
Solution of the avalanche growth equation
fIR =fd disk dustiness
OK!
Age paradox!
Gas-free modelingleads to a paradox==> gas required or episodic dust production
Bimodal histogram of fractionalIR luminosity fIR
predicted by diskavalanche process
source: Inseok Song (2004)
ISO/ISOPHOT data on dustiness vs. time Dominik, Decin, Waters, Waelkens (2003)
uncorrected ages corrected ages
ISOPHOT ages, dot size ~ quality of age ISOPHOT + IRAS
fd of beta Pic
-1.8
transitional systems 5-10 Myr age
Radiative blow-out of grains (-meteoroids, gamma meteoroids)
Dust avalanches
Radiation pressure on dust grains in disks
Neutral (grey)scattering from s> grains
Repels ISM dust Disks = Nature, not nurture!
Enhanced erosion;shortened dust lifetime
Orbits of stable -meteoroids are elliptical
Dust migrates,forms axisymmetric rings, gaps
(in disks with gas)
Short disk lifetime
Size spectrum of dust has lower cutoff
Weak/no PAH emission
Quasi-spiral structure
Instabilities (in disks)1
Age paradox
Coloreffects
Limit on fIRin gas-free disks
DUST AVALANCHES
Grigorieva, Artymowicz and Thebault (to be subm. to A&A 2005)Comprehensive model of dusty debris disk (3D) with full treatment
of collisions and particle dynamics. ■ especially suitable to denser transitional disks supporting dust avalanches
■ detailed treatment of grain-grain colisions, depending on material
■ detailed treatment of radiation pressure and optics, depending on material
■ localized dust injection (e.g., planetesimal collision)
■ dust grains of similar properties and orbits grouped in “superparticles”
■ physics: radiation pressure, gas drag, collisions
Results:■ beta Pictoris avalanches multiply debris x(3-5)
■ spiral shape of the avalanche - a robust outcome
■ strong dependence on material properties and certain other model assumptions
Model of (simplified) collisional avalanche with substantialgas drag, corresponding to 10 Earth masses of gas in disk
Main results of modeling of collisional avalanches:
1. Strongly nonaxisymmetric, growing patterns
2. Substantial exponential multiplication
3. Morphology depends on the amount and distribution of gas, in particular on the presence of an outer initial disk edge
In gas+dust disks which are optically thick in the radial direction there may be an interesting set of instabilities. Radiation pressureon a coupled gas+dust system that has a spiral density wave with wave numbers (k,m/r), is analogous in phase and sign to the forceor self-gravity. The instability is thus pseudo-gravitational in natureand can be obtained from a WKB local analysis.
Forces of selfgravity Forces of radiation pressure in the
inertial frame
Forces of rad. pressure relativeto those on the center of the arm
In gas+dust disks which are optically thick in the radial direction there may be an interesting set of instabilities. Radiation pressureon a coupled gas+dust system that has a spiral density wave with wave numbers (k,m/r), is analogous in phase and sign to the forceor self-gravity. The instability is thus pseudo-gravitational in natureand can be obtained from a WKB local analysis.
ekGi
f
ek
ierf
eik
r
e
dr
gravityself
tmkriKrad
tmkri
tmkri
1
)(10
)(10
)(10
0
0
00
4
)1(
)(
10....1.0~
)exp()exp(
0
effective coefficient for coupled gas+dust
r(this profile results from dust migration)
ekGi
f
ek
ierf
eik
r
e
dr
gravityself
tmkriKrad
tmkri
tmkri
1
)(10
)(10
)(10
0
0
00
4
)1(
)(
10....1.0~
)exp()exp(
0
Step function of r or constant
)( tmkri (WKB)
2
kG
if
Gikf
Gffff
eqPoissonG
11
11
111
2
4
4
4exp(...)
.4
ekGi
f
ek
ierf
eik
r
e
dr
gravityself
tmkriKrad
tmkri
tmkri
1
)(10
)(10
)(10
0
0
00
4
)1(
)(
10....1.0~
)exp()exp(
0
Step function of r or constant
)( tmkri (WKB)
2
kG
if
Gikf
Gffff
eqPoissonG
11
11
111
2
4
4
4exp(...)
.4
0
0)(
0211
0)(
0211
11
11
)/(
.)(1;
0
0
rrec
GQ
rec
GQ
yinstabilitgravQc
GQ
r
sorb
r
sorb
sorb
r
1
Effective Q number(radiation+selfgravity)
Analogies with gravitational instability ==> similar structures (?)
FEATURES in disks:(9 types)
blobs, clumps ■ (5)
streaks, feathers ■ (4)
rings (axisymm) ■ (2)
rings (off-centered) ■ (7)
inner/outer edges ■ (5)
disk gaps ■ (4)
warps ■ (7)
spirals, quasi-spirals ■ (8)
tails, extensions ■ (6)
ORIGIN: (10 reasons)
■ instrumental artifacts, variable PSF, noise, deconvolution etc.■ background/foreground obj.■ planets (gravity)■ stellar companions, flybys■ dust migration in gas■ dust blowout, avalanches■ episodic release of dust■ ISM (interstellar wind)■ stellar wind, magnetism■ collective eff. (self-gravity)
Many (~50) possible connections !
Not only planets but also
Gas + dust + radiation =>non-axisymmetric featuresincluding regular m=1
spirals, conical sectors, and multi-armed wavelets
Conclusion:
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