Debris Disks, Small Bodies, and Planets Alexander V. Krivov Astrophysical Institute and University Observatory Friedrich Schiller University Jena 4th Planet

Debris Disks,Small Bodies,and Planets

Alexander V. Krivov

Astrophysical Instituteand University Observatory

Friedrich Schiller University Jena

4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Components of a “mature” planetary system

1. Debris disks stem from small bodies2. Debris disks are sculptured by planets – directly and via small bodies3. Debris disks are easier to observe than planets and small bodies

=> important!

Planetesimals

Planets

Debris diskStar

Circumstellar material


Outline

●New observations●Debris disks themselves●Debris disks and small bodies●Debris disks, small bodies and

planets●Summary


New Observations

Vega

“The Big Four“ ( Lyr, Pic, Eri, PsA) revisited

Holland et al.,Nature 392, 788 (1998)

Su et al., ApJ 628, 427 (2005)Spitzer / MIPS: huge (1000AU) featureless disk seen pole-on


Eridani


Greaves et al.,ApJ 619, L187 (2005)

JCMT / SCUBA five years after discovery:signs of rotation, at least three features real



Pic



Galland et al.,AAp 447, 355 (2006)

New radial velocity constraints onpresumed planets: no Jupiter inside 1AU

Wahhaj et al. (2003)Weinberger et al. (2003)Telesco et al. (2005)

New images of the inner disk (<100AU)

AU Mic

New disks resolved (vis, IR, sub-mm)

Kalas et al. Science 303, 1990 (2004)Liu, Science 305, 1442 (2004)


M1Ve0.5 Msun

0.1 Lsun

~20 Myr9.9 pc

vis and NIR,88” U. Hawaiiand Keck

Coeval with Pic, but an M-type star

HD 32297

Greaves et al., MNRAS 351, L54 (2004)

Schneider et al., ApJ 629, L117 (2005)Kalas, ApJ, 633, L169 (2005)

Cet

New disks resolved (vis, IR, sub-mm)


A030 Myr?110 pc

vis and NIR,NICMOS and88” U. Hawaii

G8V, ~10 Gyr, 3.7 pcsub-mm, JCMT / SCUBA

Older than the Sun!

More than 300 disks in total

Meyer et al., ApJS 154, 422 (2004)

Many more unresolved disks (IR excesses)


Greaves, Science 307, 68 (2005)

Statistics: age dependence

Protoplanetary disks

Transitional disks

Debris disks

Large drop after 10Myr

No change after 400Myr, a linear decay instead (cf. Habing et al., Nature 401, 456 ,1999)

No obvious dependence on central star's properties


Statistics: stars with disks vs stars with planets

...but (almost) no stars with RV planets have debris disks

Greaves et al., MNRAS 348, 1097 (2004)

Nearly all stars with debrisdisks have distant planets

Saffe & Gomes (2004) and Beichman et al (2005) came to different conclusions. The question remains open...


Debris DisksThemselves

Birth, life, and death of dust grains


Dust sources:● planetesimals (collisions)● comets (activity) ● grain-grain collisions

Dust sinks:● sublimation● collisions and RP blowout● ejection by planets

Dust evolution:● Stellar gravity● Direct radiation pressure● Poynting-Robertson drag● Grain-grain collisions● Gas drag ● Gravity of planets● Lorentz force

Birth, life, and death of dust grains


Direct radiation pressure only “reduces” the mass of the star,dust grain orbits remain Keplerian

Stellar gravity + radiation pressure


Talks by Gerhard Wurm & Oliver Krauss


●-meteoroids (in bound, elliptic orbits)●two types of -meteoroids (in unbound, hyperbolic orbits)



A typical boundary between - and -meteoroids: 1-10 m


● Orbits of -meteoroids shrink and circularize● The grains eventually sublimate near the star

Wyatt & Whipple, ApJ 111, 134 (1950)Breiter & Jackson, MNRAS 299, 237 (1998)

Poynting-Robertson drag


Collisions

Collisional grinding: pebbles ... sand ... fine dust...

Rates

Min relative velocity for fragmentation: ~100m/sRandom velocities in a disk: ~1km/s => collisions are disruptive

Largest fragment's mass / collider's mass(assuming 1km/s relative velocity): ~10-3

=> pounding is efficient

Outcomes

Collisional time ~ orbital period 10 optical depth

~ 10-1000 orbital periods

=> collisions are frequent


Poynting-Robertson drag vs collisions

Zodiacal cloud Pictoris

Krivov, Mann & Krivova, AAp 362, 1127 (2000)Leinert & Grün, In Phys.of Inner Heliosphere (1990)

Except in old dilute disks, P-R drag plays a minor role!


Contradictory observations of Pic and AU Mic (12Myr):much gas (gas:dust ~ 100:1) Thi et al. (2001), Brandeker et al. (2004),...

little gas (gas:dust < 6:1) Lecavelier et al. (2001), Roberge et al. (2005),...

Dynamical arguments:very little gas (gas:dust < 1:1) Thebault & Augereau, AAp 437, 141 (2005)

Consequences:gas planets must already have formed there,and there is evidence for that (e.g., Mouillet et al. 1997, Liu 2004)

Gas drag


Talk by Inga Kamp

Size distribution (the Vega disk example)

Dohnanyi's (1969) power law(alpha-meteoroids only)

Krivov, Löhne & Sremcevic, AAp (submitted)


Poster by Torsten Löhne

beta-meteoroids





...timescales depend on distance...









Dominant size, waviness, presence of -meteoroids

The steady state distribution





There is an upper limit on the radial slope

Radial distribution (the Vega disk example)


The steady state distribution

Debris Disksand Small Bodies

Short-term evolution of debris disk

Supercollision

Dust clump

Longitudinal spreadand formationof a dust ring

Radial spread outwardin ~0.1-1 Myr

Non-steady-state: e.g. due to recent major collisions (Wyatt & Dent, MNRAS 334, 589, 2002; Kenyon & Bromley, AJ 130, 269, 2005)




Long-term evolution of debris disk

Collisional depletion of parent bodies (Dominik & Decin, ApJ 598, 626, 2003)

EKB

Krivov, Sremcevic & Spahn, Icarus 174, 105, (2005)


Long-term evolution of debris disk

A nearly 1/ t decay of parent body populations should causegradual depletion of debris disks over Gyr-scales

Collisional depletion of parent bodies (Dominik & Decin, ApJ 598, 626, 2003)


EKB

Krivov, Sremcevic & Spahn, Icarus (2005)

Vega disk


Debris Disks,Small Bodies,and Planets

Global structure – asymmetries and warps

Observed in several resolved disks


warp is spreading outwards (Mouillet et al., AAp (1997):

Rwarp

=Rwarp

(Mstar

, Mplanet

, aplanet

, time)

Offset (e, Warp (i,

Global structure – asymmetries and warps

Suggested explanation: secular perturbations from an embedded planet

(alternatively, asymmetry can stem from the disk-ISM interaction)Artymowicz & Clampin, ApJ (1997)


Radial substructure - inner gaps

Seen in resolved disks Inferred from SEDs

Moro-Martin, Wolf & Malhotra, ApJ 621, 1079 (2005)

Curves: w/o planets, grey bands: with planets

Inner gaps with radii of a few to a few tens of AU are found to be typical



Talk by Sebastian Wolf

Both scenarios look plausible,both require a planet to confine the planetesimal belt

Radial substructure - inner gaps

Scenario I:●Dust production in a planetesimal belt●P-R drift of dust inward to planet orbit●Planet acts as a dynamical barrier

Scenario II (simpler, robuster!)●Dust production in a planetesimal belt●Subsequent collisional cascade●RP spreads dust outward from the belt


Spatially-resolved spectrophotometry:evidence for several rings

of fine dust

Okamoto et al., Nature 431, 660 (2004)

Radial substructure - rings

Wahhaj et al. (2003)Weinberger et al. (2003)Telesco et al. (2005)

Images: evidence for several rings

of large dust

Observed in several resolved disks


Poster by Florian Freistetter

Both scenarios look plausible

Radial substructure - rings

Scenario I:●Dust production “somewhere” outside●P-R drift of dust inward to resonances●Ring formation almost at planet orbit

Scenario II (simpler, robuster!)●Dust production in a planetesimal belt●Therefore, higher dust density there●Ring appears at the belt location

Dermott et al, Nature 369, 719 (1994)

A simple kinetic model: localized dust production,

P-R drag and collisionsWyatt, AAp 433, 1007 (2005)


Liou et al. (2000):~1M

J, a

p=40AU, e

p=0.01

Ozernoy et al. (2000):0.2M

J, a

p=55-65AU, e

p=0

Quillen & Thorndike (2002):0.1M

J, a

p=42AU, e

p=0.3

Deller & Maddison (2005):the same + 2nd planet @ 10-18 AU

Eridani

Azimuthal substructure - clumps


Quillen & Thorndike,ApJ 578, L149 (2002)

Observations Models


Poster by Martina Queck

Edgeworth-Kuiper belt


Observations Models

...none ...

Liou & Zook, AJ 118, 580 (1999)


Theory(trapping efficiency, timescales etc)

(Beauge, Ferraz-Mello, Jackson, Lazzaro, Liou,Roques, Scholl, Sicardy,Weidenschilling, ... (1990s)

Star Planet

Voids

Clumps

Inner gap

Standard scenario: P-R drift & trapping in exterior MMRs



Difficulties with this scenario


P-R timescale and timescale of resonant eccentricity pumping>> timescale of collisional destruction !



Works only in disks with > 10-5!

Krivov, Queck & Sremcevic, in prep.

Standard scenario:●Dust production in a planetesimal belt●P-R drift of dust inward to resonances●Capture and formation of clumps

Wyatt, ApJ 598, 1321 (2003)

Alternative scenario:●Dust production in a family of resonant planetesimals●Dust remains in the same resonance

Works always (but requires~0.1-1 Mearth in planetesimals)


Poster by Martina Queck

Summary

Debris disks are:

• a natural component of planetary systems at later evolutionary stages, and therefore important objects to study;

• maintained by, and deliver information on, small body populations;

• indicators of planets;


Studies of debris disks complete the census of planetary systems and can certainly contribute to

answering the great question:“How do the planetary systems form

and evolve?”


Many thanks to my collaborators

Torsten Löhne (poster!)

Martina Queck (poster!)

Florian Freistetter (poster!)

Documents

Debris Disks, Small Bodies, and Planets Alexander V. Krivov Astrophysical Institute and University Observatory Friedrich Schiller University Jena 4th Planet