Great Migrations

1
AST3020. Lecture 09 Theory of
transitional and debris disks
The roles of radiation pressure Beta Pictoris as
a young solar system Some observed examples and
their non-symmetric morphology Possible
mechanisms of structure formation
artifacts or background objects planets and
stars internal disk dynamics local dust
release avalanche intrinsic disk
instabilities (optically thick disks)

2
Weak/no PAH emission
Neutral (grey) scattering from sgt? grains
Repels ISM dust Disks Nature, not nurture!
Size spectrum of dust has lower cutoff
Radiative blow-out of grains (??-meteoroids,
gamma meteoroids)
Radiation pressure on dust grains in disks
Instabilities (in disks)
Dust avalanches
Orbits of stable ?-meteoroids are elliptical
Quasi-spiral structure
Dust migrates, forms axisymmetric rings, gaps
(in disks with gas)
Limit on fIR in gas-free disks
Color effects
Enhanced erosion shortened dust lifetime
Short disk lifetime
Age paradox
3
(No Transcript)
4
(No Transcript)
5
Structure in transitional and debris disks -
very common - visibly non-axisymmetric
6
(No Transcript)
7
AB Aur disk or no disk?
Fukugawa et al. (2004)
another Pleiades-type star
no disk
8
Hubble Space Telescope/ NICMOS infrared camera
9
HD 141569A is a Herbig emission star gt2 x solar
mass, gt10 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
10
HD 14169A disk gap confirmed by new
observations (HST/ACS)
11
HD141569BC in V band
HD141569A deprojected
HST/ACS Clampin et al.
12
The danger of overinterpretation of
structure Are the PLANETS responsible for
EVERYTHING we see? Are they in EVERY system? Or
are they like the Ptolemys epicycles, added
each time we need to explain a new
observation?
13
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)
14
FEATURES in disks blobs, clumps ? streaks,
feathers ? rings (axisymm) ? rings
(off-centered) ? inner/outer edges ? disk
gaps ? warps ? spirals,
quasi-spirals? tails, extensions ?
ORIGIN ? instrumental artifacts, variable
PSF, noise, deconvolution etc.
15
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/ foreground objects
16
?
Source P. Kalas
17
AU Microscopii and its less inclined cousin
This is a coincidentally(!) aligned background
galaxy
18
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
Stellar and planetary perturbations
gt interesting prospect of finding planets by
their imprint on dust
19
Kalas and Larwood initially thought they detected
ripples on one side of the Beta Pic disk. Later,
evidence for the reality of most ripples
disappeared.
20
Structure from stellar encounter
Doesnt work in case of beta Pic (despite claim
by Kalas and Larwood ca. 2001) model was
oversimplified no radiation pressure on dust, no
size distribution pure N-body unlikely if
single passage P1e-6 binary gt ok, but
repeated encounters delete structure rings an
artifact of a sharp edge in initial distribution
of particles
21
No ring features in more accurate
simulations (Jeneskog, B.Sc. Thesis 2003)
22
Stellar flyby (of an elliptic-obit companion)
explains some features of HD 141569A
Augereau and Papaloizou (2003)
Application to Beta Pictoris less certain...
23
Resonant pileup of dust due to planets
24
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 -- thats
very tough to do! Resultant planets depend on all
this.
Beta 0.01 (monodispersed)
Vega
25
Warp from inclined planet (model of beta
Pictoris), Wyatt Augereau Paploizou.
26
The danger of overinterpretation of
structure Are the PLANETS responsible for
EVERYTHING we see? Are they in EVERY system? Or
are they like the Ptolemys epicycles, added
each time we need to explain a new
observation?
27
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
28
Type 0 (gas drag radiation pressure) Gas
drag Keplerian circular orbital velocity of
solids, slightly subkeplerian rotation of gas in
disk (pressure gradients) headwind, orbital
decay (inward) (Adachi 1976, Weidenschilling
1977, ...) Gas drag radiation pressure
strongly subkeplerian orbital speed of solids
affected by stellar radiation pressure
back-wind, fast outward migration
(TakeuchiArtymowicz 2001, Lin Klahr 2002,
Thebault, Lecavelier, )
29
(No Transcript)
30
Migration Type 0

• Dusty disks structure from gas-dust coupling
  (Takeuchi Artymowicz 2001)
• theory will help determine gas distribution

Predicted dust distribution axisymmetric ring
Gas disk tapers off here
31
Dust avalanches and implications -- upper
limit on dustiness -- the division of disks into
gas-rich, transitional and gas-poor --
non-axisymmetry ! Other reasons ISM
sandblasting
radiative instabilities
32
Weak/no PAH emission
DUST AVALANCHES
Neutral (grey) scattering from sgt? grains
Repels ISM dust Disks Nature, not nurture!
Size spectrum of dust has lower cutoff
Radiative blow-out of grains (??-meteoroids,
gamma meteoroids)
Radiation pressure on dust grains in disks
Instabilities (in disks)
Dust avalanches
Orbits of stable ?-meteoroids are elliptical
Quasi-spiral structure
Dust migrates, forms axisymmetric rings, gaps
(in disks with gas)
Limit on fIR in gas-free disks
Color effects
Enhanced erosion shortened dust lifetime
Short disk lifetime
Age paradox
33
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
34
Dust Avalanche (Artymowicz 1997)
Process powered by the energy of stellar
radiation N exp (optical thickness of the disk
ltdebris/collisiongt)
N
disk particle, alpha meteoroid ( lt 0.5)
sub-blowout debris, beta meteoroid ( gt 0.5)
35
Ratio of the infrared luminosity (IR excess
radiation from dust) to the stellar
luminosity it gives the
percentage of stellar flux
absorbed, then re-emitted thermally
the midplane optical thickness
multiplication factor of debris in 1 collision
(number of
sub-blowout debris)
Simplified avalanche equation
Solution of the simplified avalanche growth
equation
The above example is relevant to HD141569A, a
prototype transitional disk with interesting
quasi-spiral structure. Conclusion
Transitional disks MUST CONTAIN GAS or face
self-destruction. Beta Pic is among the most
dusty, gas-poor disks, possible.
36
) derivation
37
Bimodal histogram of fractional IR luminosity
fIR similar to that predicted by disk avalanche
process
38
source Inseok Song (2004)
Bimodal histogram of fractional IR luminosity
fIR similar to that predicted by disk avalanche
process
39
ISO/ISOPHOT data on dustiness vs. time
Dominik, Decin, Waters, Waelkens (2003)
uncorrected ages
corrected ages
-1.8
ISOPHOT ages, dot size quality of age
ISOPHOT IRAS
fd of beta Pic
40
transitional systems 5-10 Myr age
41
Grigorieva, Artymowicz and Thebault (AA,
2006) 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 up to 200! ? spiral
OR blob-like shape of the avalanche ? 50-500 km
bodies must collide for observability in the
innerb Pic disk, which isnt very probable ?
strong dependence on material properties and
certain other model assumptions, but mostly
on disk dustiness 3 times larger than b Pic gt
planetesimal collisions likely!
42
(No Transcript)
43
OK!
Gas-free modeling leads to a paradox gt gas
required or episodic dust production
Age paradox!
fIR fd disk dustiness
44
Model of (simplified) collisional avalanche with
substantial gas drag, corresponding to 10 Earth
masses of gas in disk
45
Main results of modeling of collisional
avalanches 1. Strongly nonaxisymmetric, growing
patterns 2. Substantial almost exponential
multiplication 3. Morphology depends on the
amount and distribution of gas, in particular on
the presence of an outer initial disk edge
46
Best model, Ardila et al (2005)
Beta 4 H/r 0.1 Mgas 50 ME
5 MJ, e0.6, a100 AU planet
HD 141569A
47
Spontaneous axisymmetry breaking in
optically thick disks results in structure
resembling gravitational instability
48
In gasdust disks which are optically thick in
the radial direction there may be an interesting
set of instabilities. Radiation pressure on a
coupled gasdust system that has a spiral density
wave with wave numbers (k,m/r), is analogous in
phase and sign to the force or self-gravity. The
instability is linear, pseudo-gravitational, and
can be obtained from a WKB local analysis.
Forces of selfgravity
Forces of radiation pressure in the inertial
frame
Forces of rad. pressure relative to those on the
center of the arm
49
In gasdust disks which are optically thick in
the radial direction there may be an interesting
set of instabilities. Radiation pressure on a
coupled gasdust system that has a spiral density
wave with wave numbers (k,m/r), is analogous in
phase and sign to the force or self-gravity..
effective coefficient for coupled gasdust
(this profile results from dust migration)
r
50
Step function of r or constant
2
(WKB)
51
Step function of r or constant
2
(WKB)
52
Effective Q number (radiationselfgravity)
1
r
Analogies with gravitational instability gt
similar structures (?)
53
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 !
54
Conclusion
Not only planets but also Gas dust radiation
gt non-axisymmetric features including
regular m1 spirals, conical sectors,
and multi-armed wavelets, as
well as blobs