stsci nrdd, 20 oct 2005

STScI NRDD, 20 Oct 2005

1. Structures vs. reasons (planets,…)2. Dust, avalanches, fIR, gas, and the calssification of disks3. HD 141569A4. Non-axisymmetric features without planets

Pawel ArtymowiczUniversity of Toronto

New edge-on disk

NICMOS/HST

(Schneideret al 2005)

Optical thickness

Dust density

Radius r [AU] Height z [AU]

STIS/Hubble imaging (Heap et al 2000)

Modeling (Artymowicz,unpubl.):parametric, axisymmetric diskcometary dust phase function

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?

Also, do we really need a new type of particlefor every bandpass [optical, sub-mm]?

FEATURES in disks: (9)

blobs, clumps ￭streaks, feathers ￭rings (axisymm) ￭rings (off-centered) ￭inner/outer edges ￭disk gaps ￭warps ￭spirals, quasi-spirals ￭tails, extensions ￭

ORIGIN: (10)

￭ 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 eff. (selfgravity)

(Most features additionally depend onthe viewing angle)

FEATURES in disks:

blobs, clumps ￭streaks, feathers ￭rings (axisymm) ￭rings (off-centered) ￭inner/outer edges ￭disk gaps ￭warps, incl. disks ￭spirals, quasi-spirals ￭tails, extensions ￭

ORIGIN:

￭ instrumental artifacts, variable PSF, noise, deconvolution etc.

FEATURES in disks:

blobs, clumps ￭streaks, feathers ￭rings (axisymm) ￭rings (off-centered) ￭inner/outer edges ￭disk gaps ￭warps ￭spirals, quasi-spirals ￭ tails, extensions ￭

ORIGIN:

￭ background orforeground objects

AB Aur : disk or no disk?

Fukugawa et al. (2004)

another “Pleiades”-type star

no disk

Source: P. Kalas

?

AU Microscopii & a less inclined cousin

This is a coincidentally(!) aligned background galaxy

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?

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

Hubble Space Telescope/ NICMOS infrared camera

HD 14169A disk gap confirmed by new observations (HST/ACS)

HD141569+BC in V band HD141569A deprojected

HST/ACS Clampin et al.

Outward migration of protoplanets to ~100AU

or

outward migration of dust to form rings and spirals

required to explain the structure in transitional (5-10 Myr old) dust disksand perheps also the (12-20Myr old) Beta Pictoris-type disks

Type III

DISK-PLANET interactionand migration, including outward migration

It used to be just type I and II...now we study a new mode of migration:

type III

Migration Type I :embedded in fluid

Migration Type II :more in the open (gap)

Migration Type I :embedded in fluid

Migration Type III partially open (gap)

Migration Type II :in the open (gap)

Migration:

type 0

type I

type II & IIb

type III

N-body

Timescale of migration:

from ~1e2 yr to disk lifetime (~1e7 yr)

> 1e4 yr

> 1e5 yr

> 1e2 - 1e3 yr

> 1e5 yr (?)

Interaction:

Gas drag + Radiation press.

Resonant excitation of waves (LR)

Tidal excitation of waves (LR)

Corotational flows (CR)

Gravity

……………………………………………………………………….

Shepherding by

Prometheus and Pandora

Pan opens Encke gap in A-ring of Saturn

Planets were thought to always shepherd planets…or was itthe other way around?

A gap-opening body in a disk: Saturn rings, Keeler gap region (width =35 km)This new 7-km satellite of Saturn was announced in May 2005.

To Saturn

Prometheus (Cassini view)

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)

Type I -- III migration

Tim

e-sc

ale

( y

e ars

)

Figure From: “Protostars and Planets IV (2000)”;Artymowicz (this talk).

type III

Simulation of a Jupiter-class planet in a constant surface density disk with soundspeed = 0.05 times Keplerian speed.PPM = Piecewise Parab. MethodArtymowicz (2000),resolution 400 x 400

Although this is clearly a type-II situation (gap opens), the migrationrate is NOT that of the standard type-II, which is the viscous accretionspeed of the nebula.

Consider a one-sided disk (inner disk only). The rapid inward migration is OPPOSITE to the expectation based on shepherding (Lindblad resonances).

Like in the well-known problem of “sinking satellites” (small satellite galaxies merging with the target disk galaxies),Corotational torques cause rapid inward sinking. (Gas is trasferred from orbits inside the perturber to the outside.To conserve angular momentum, satellite moves in.)

Now consider the opposite case of an inner hole in the disk. Unlike in the shepherding case, the planet rapidly migrates outwards.

Here, the situation is an inward-outward reflection of the sinking satellite problem. Disk gas traveling on hairpin (half-horeseshoe) orbits fills the inner void and moves the planet out rapidly (type III outward migration). Lindblad resonances produce spiral waves and try to move the planet in, but lose with CR torques.

NO MIGRATION:In this frame, comoving with the planet, gas has no systematic radial velocity V = 0, r = a = semi-major axis of orbit.

Symmetric horseshoe orbits, torque ~ 0

r

a

0

disk

Librating Corotational (CR) region

Librating Hill sphere (Roche lobe) region

xCR

protoplanet

xCR = half-width of CR region, separatrix distance

SLOW MIGRATION:In this frame, comoving with the planet, gas has a systematic radial velocity V = - da/dt = -(planet migr.speed)

asymmetric horseshoe orbits, torque ~ da/dt

FAST MIGRATION:CR flow on one side of the planet, disk flow on the other

Surface densities in the CR region and the disk are, in general, different.

Tadpole orbits, maximum torque

r

r

a

0

0

a

Saturn-mass protoplanet in a solar nebula disk (1.5 times the Minimum Nebula,PPM, Artymowicz 2003)

Type III outwardmigration

Condition for FAST migration:disk mass (in CR region)similar to planet mass.

Notice a carrot-shaped bubble of“vacuum” behind the planet. Consisting of material trappedin librating orbits, it producesCR torques smaller than the matrial in front of the planet. The net CR torque powers fast migration.

radius1 2 3

Azimuthalangle (0-360 deg)

Summary of type-III migration Extremely rapid (timescale < 1000 years). CRs >> LRs, disks

do not shepherd planets. Requires sufficient disk density Direction depends on prior history, not just on disk properties. Supersedes a much slower, standard type-II migration (&type I ??) Migration stops on disk features (rings, edges and/or substantial

density gradients.) Such edges seem natural (dead zone boundaries, magnetospheric inner disk cavities, formation-caused radial disk structure)

Offers possibility of survival of giant exoplanets at intermediate distances (0.1 - 1 AU),

...and of terrestrial planets during the passage of a giant planet on its way to the star (last Mohican scenario)

STRUCTURE in OUTER REGIONS of dusty transitional & debris disks

FEATURES in disks:


ORIGIN:

￭ stellar companions, flybys

Augereau and Papaloizou (2003)

Stellar flyby (of an elliptic-obit companion) explains some featuresof HD 141569A

Application of the idea to Beta Pictoris less certain...

Quillen et al. (2004)

HD 141569A

Lin

ear

dust

pro

d.Q

uadr

atic

pro

d.H/r = 0.05 H/r =0.1 LTE

Ardila et al (2005) Flyby+planetesimals --> dust production & outflow

= 4Mgas = 50 ME

Lin

ear

dust

pro

d.Q

uadr

atic

pro

d.No planet 5 MJ, e=0.6 planet

Ardila et al (2005) Flyby+plane+planetesimals

= 4H/r = 0.1Mgas = 50 ME

Beta = 4H/r = 0.1Mgas = 50 ME

Best model, Ardila et al (2005)

HD 141569A

5 MJ, e=0.6, a=100 AUplanet

Room for improvement in theory

Wyatt (2005) - planetesimal evolution under seclural perturbation from an eccentric planet, initial time evolution of pericenter glow. 1. No gas drag 2. No dust 3. Planet acts on gas disk to produce spiral waves (in gas and dust) at Lindblad resonances.Ardila et al (2005)

1. Sharp outer edge at 1*pericenter distance of flyby * 2. No pre-existing dust in disk, only the dust produced after perturbation (no time for that?) 3. Single beta value, 4. No dust-dust collisions or avalanches

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

1 Myr

5 Myr

12-20 Myr

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

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

How radiation pressure induces large eccentricity:

= F_rad / F_grav

Dust Avalanche (Artymowicz 1997)

= disk particle, alpha meteoroid ( < 0.5)

= submicron debris, beta meteoroid ( > 0.5)

N ~ exp (optical thickness of the disk * #debris/coll)

N

For instance, in HD141569A, a prototype transitional disk

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

Bimodal histogram of fractionalIR luminosity fIR

predicted by diskavalanch process.

From: Inseok Song

Disk dustiness

OK!

paradox!

Gas-freemodelingleads to paradox==> gas required


Dust avalanches







(in disks with gas)

Short disk lifetime





Age paradox

Coloreffects

Limit on fIRin gas-free disks

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 by 3-5

￭ spiral shape of the avalanche 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 disk edge

FEATURES in disks:


ORIGIN:

￭ ISM (interstellar wind: gas + dust bombardment)

Artymowicz & Clampin (1997)

FEATURES in disks:


ORIGIN:

￭ stellar influence:photoevaporation, wind, magnetism


Dust avalanches







(in disks with gas)

Short disk lifetime





Age paradox

Coloreffects

FEATURES in disks:


ORIGIN:

￭ collective effects (e.g., disk selfgravity, radiative instability)

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.

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 coeffiient for coupled gas+dust

r(result of dust migration)

ekGi

f

ek

ierf

eik

r

e

dr

gravityself

tmkriKrad

tmkri

tmkri

1

)(10

)(10

)(10

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)1(

)(

10....1.0~

)exp()exp(

0

Step function of r or constant

)( tmkri (WKB)

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 numberradiation+selfgravity

Analogies with gravitational instability --- similar structures (?)

Not only planets but also

Gas + dust + radiation = non-axisymmetric features including regular m=1 spirals, conical sectors, and multi-armed wavelets

FEATURES in disks:(9)

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)

￭ 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. (selfgravity)

48 POSSIBLE CONNECTIONS !

While observing: don't try to prove one theory (like, that there MUST BE planets in your still poorly-observed disk. They may be there, but making such a claim requires good evidence.)

While modeling: take good care! Don't claim success easily. Your model does NOT fit all the data. Include all relevant physics/dynamics. Use multi-wavelength sets of data to dramatically improve uniqueness of the model.

THE END

stsci nrdd, 20 oct 2005

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