Understanding the extrasolar planetary systems : observations & theories of disks and planets Pawel...

transcript

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

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

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)

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

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)

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

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

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?

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

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

~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

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)

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

Eccentricity of exoplanets vs. a and m sini

m, a, e somewhat correlated: a e ? m

a e ? m

Gravitational Instabilityand the Giant GaseousProtoplanet hypothesis

Gravitational stability requirements

numberToomreSafronovGc

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

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)

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

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

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

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

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

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 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.

sm / 2

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:

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:

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:

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

12-20 Myr

Gas pressure force

vgv=vK

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

Dust avalanches

(in disks with gas)

Short disk lifetime

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:

ORIGIN:

￭ dust blowout avalanches,￭ episodic/local dust release

Dust avalanches

(in disks with gas)

Short disk lifetime

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>)

The above example is relevant to HD141569A, a prototype transitional disk (with interesting quasi-spiral structure.) Conclusion:

10~)20exp(~)exp(/

2.0018.0)1.0(

)2/()/()/(

)2/()4/(2

rdrzrdrs

rdrrrdrf

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

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

transitional systems 5-10 Myr age

Dust avalanches

Orbits of stable -meteoroids are elliptical

(in disks with gas)

Short disk lifetime

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.

gravityself

tmkriKrad

10....1.0~

)exp()exp(

effective coefficient for coupled gas+dust

r(this profile results from dust migration)

gravityself

tmkriKrad

10....1.0~

)exp()exp(

Step function of r or constant

)( tmkri (WKB)

eqPoissonG

4exp(...)

gravityself

tmkriKrad

10....1.0~

)exp()exp(

Step function of r or constant

)( tmkri (WKB)

eqPoissonG

4exp(...)

yinstabilitgravQc

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:

Understanding the extrasolar planetary systems : observations & theories of disks and planets Pawel...

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