Observations, Modeling and Theory of Debris Discs · 2013. 9. 9. · Eiroa et al. 2013 Sibthorpe et...

Observations, Modeling and Theory of Debris Discs

Brenda Matthews (HIA, Canada)

Geoff Bryden (JPL) Carlos Eiroa (Universidad Autonoma de Madrid)

Alexander Krivov (University of Jena) Mark Wyatt (Institute of Astronomy)

Physical picture

•  Debris disks are produced from the remnants of the planet formation process

•  They are evidence that systems were able to produce at least planetesimal-scale oligarchs (100s of km)

•  Second generation dust is produced through collisional processes

•  Debris discs include –  Planetesimals (unseen), potentially in

narrow “birth rings” –  Dust produced from collisions (detected

optical centimetre) –  All size scales in between

Courtesy: Zoe Leinhardt 05/28/13 Protostars & Planets VI

Onset of Debris phase

Hernandez et al. 2008, 686, 1195

Panić et al. 2013, MNRAS, accepted (after Wyatt 2008 ARA&A, 46, 339)

Protoplanetary Dust from 0.1 – 100 AU Massive gas disk Accretion onto star Optically thick

Debris Dust in belts No gas No accretion Optically thin

10 Myr

05/28/13 Protostars & Planets VI

Detecting Debris Discs

Scattered light

Shows up subtle structures Highlights position of small

grains Extent of outer disc/halos Does not trace planetesimal

“birth ring” Inner region blocked

Thermal emission

Highlights larger grains Can reveal hot/warm/cold

components Can trace the “birth ring” of

planetesimals Resolution has been a

limitation in the past

Protostars & Planets VI 05/28/13

See poster 2B072 (Debes)

Dust replenished by km-sized planetesimals

Debris disks stirred somehow

Cleared inner regions & eccentric rings

Some disks are asymmetric

Some systems actually have planets Kalas et al. (2008)

Why we think debris systems could have planets

Nature / ISAS / JAXA 05/28/13 Protostars & Planets VI



Cleared inner regions & eccentric, offset rings


Some systems actually have planets


Kalas et al. 2008, Science, 322, 1345

Marshall et al. 2011, A&A, 529, 117






Some systems actually have planets


Greaves et al. 2013, in preparation

HD 202628

Krist et al. 2002






Some systems actually have planets Kalas et al. (2008)


Heap et al. 2000, ApJ, 539, 435; Golimowski et al. 2006, AJ, 131, 3109; Lagrange et al. 2010, Science, 329, 57 05/28/13 Protostars & Planets VI

1.  Secular perturbations

The orbits of disk particles can be affected by a planet’s gravity in 3 ways:

2. Resonances

eccentric planet

inclined planet

3. Scattering

3 ways planets interact with discs

Movies from Mark Wyatt

See poster 2B075 (Dawson)

The challenge: ��Debris discs are faint

Protostars & Planets VI

Su et al. 2006, ApJ, 653, 675; Eiroa et al. 2013, A&A, in press; Trilling et al. 2008, ApJ, 674, 1086; Matthews et al. 2013, in preparation

10-4

10-5

10-6

10-7

Blue: A stars (Su06) Red: FGK stars (E13) Green: FGK stars (T08) Purple: AFGKM (M13)

M K G F A

05/28/13

Incidence rates


Note that surveys each have their own excess limit that is detectable. It is possible that all stars have discs at some level with many below the detection thresholds.

A stars

25-35%

2.2, 24, 70, 100 um

Chen et al. 2012, ApJ, 756, 133 Chen et al. 2011, ApJ, 738, 122 Su et al. 2006, ApJ, 653, 675 Absil et al. 2013, Thureau et al. 2013, in prep

Excellent agreement at all wavelengths. Decreases with age.

FGK stars M stars

3 - 20%

24, 70, 100/160 um

Carpenter et al. 2009 Hillenbrand et al. 2008 Trilling et al. 2008 Eiroa et al. 2013 Sibthorpe et al. 2013, in prep

Increasing incidence with wavelength. Decreases with age to ~ 1Gyr.

Very few!

24, 70, 100, 850 um

Gautier et al. 2007 Liu et al. 2004 Lestrade et al. 2006 Lestrade et al. 2013 Matthews et al. 2013, in prep

Except for very young M stars, generally these discs remain elusive.

05/28/13

Comparable to rate of planets around FGK stars (16%) from Kepler with periods up to 85 days (Fressin et al. 2013)

Dust excess evolution

•  Spitzer studies of the 24 and 70 excesses (Ftot/F*) of A stars found a ∝ t-1 decline in the upper envelope on decay timescale of 150 Myr at 24 µm but longer (~400 Myr) at 70 µm

Rieke et al. 2005, Su et al. 2006 05/28/13 Protostars & Planets VI

Spitzer A star evolution

•  Luminosity decline relative to the star is evident •  24 micron excess declines fastest (~0 by 400 Myr), suggesting an inside out

evolution of the dust (warmer dust is lost first) Su et al. 2006

KB


See poster 2B070 (Vican)

Long term evolution

•  Steady-state cascade implies that, at any age, disc cannot be dustier than a certain limit

•  Most discs are consistent with this and are “KBs”

•  systems with hot dust are not consistent with this picture


Wyatt et al. 2007; Loehne et al. 2008

05/28/13

See poster 2B071 (Bonsor)

edge-‐on view of a planetary system

distance increases

temperature decreases

planetesimal belt

terrestrial planets

giant planets disk halo

∼1500 K

∼300 K terrestrial

zone ∼150 K asteroidal

zone

∼50 K Kuiper-‐belt

zone wavelength increases

2 µm ∼10 µm ∼24 µm ∼60-‐70 µm

very hot hot warm cold

Zones of dust


See poster 2B074 (van Lieshout)

Wavelength and Resolution


SCUBA: Holland et al. 1998, Nature, 392, 788 Spitzer: Stapelfeldt et al. 2004, ApJS, 154, 458 HST: Kalas et al. 2005, Nature, 435, 1067 Herschel: Acke et al. 2012, A&A, 540, 125 ALMA: Boley et al. 2012, ApJ, 750, 21

Spitzer

SCUBA 05/28/13

Resolved Kuiper Belts

F-star Gamma Dor (Broekhoven-Fiene et al. 2013)


•  DUNES and DEBRIS both find ~50% detected discs are resolved

•  wealth of information from resolved images & SEDs •  fit Tdust, rdisc, spectral slope •  Inclination, position angle •  find Ldust/Lstar, Mdisc, rdisc/rblackbody •  Dust grain sizes/compositions

See posters 2B073 (Pawellek) 2B069 (Schüpper)

Alignment of discs and stars

12 systems have disc and stellar inclinations independently

measured (incl. Sun)


!"""

!""!#$%&!'$!()!*+$,*!'-./'

#$%&'%()& &$*#('%()&

"+"

"+,

-+"

-+,

.+"

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0%12'%3'4''#502'%6'

%1#7%1+$%51'5"''6%0#'-6!8*!!0/'

1&2$ 34567!! 385--"6!7 2$99$58:*;

Halos: HR 8799

•  Cold, very extended extensions of debris

discs, dominated by blow-out grains on hyperbolic or bound orbits

•  Planetesimal belt: 100 – 310 AU •  Halo: 310 – 2000 AU


10-1 100 101 102 103wavelength (!m)

10-3

10-2

10-1

100

101

F (J

y)

10-3

10-2

10-1

100

Surf

ace

brig

htne

ss (m

Jy/a

rcse

c2)

70µm

Raw ModelModel convolvedMedian DataData

39.4 394.Radial distance (AU)

10-3

10-2

10-1

100

Surf

ace

brig

htne

ss (m

Jy/a

rcse

c2)

100µm

1 10Radial distance (")

10-2

10-1

100

Surf

ace

brig

htne

ss (m

Jy/a

rcse

c2)

160µm

10-3

10-2

10-1

100

Surf

ace

brig

htne

ss (m

Jy/a

rcse

c2)

70µm

Raw ModelModel convolvedMedian DataData

39.4 394.Radial distance (AU)

10-3

10-2

10-1

100

Surf

ace

brig

htne

ss (m

Jy/a

rcse

c2)

100µm

1 10Radial distance (")

10-2

10-1

100

Surf

ace

brig

htne

ss (m

Jy/a

rcse

c2)

160µm

153 K 36 K

λ0 ~ 47 +/- 30 µm β ~ 1.0 +/- 0.1

Matthews et al. 2013, in prep 05/28/13

G2V star with no evidence of a halo and no detected planets

Evidence of transport of material inward in the disc

Disc appears larger with increasing wavelength

Marshall et al. A&A 529,A117 (observational)Löhne et al. A&A 537, A110 (detailed modelling)

HD 207129


Cold disc candidates

•  Six "cold disk" candidates. These disks have temperatures close to blackbody.

•  They may be belts of unstirred primordial macroscopic grains that failed to grow to planetesimal sizes.


Krivov et al. 2013, ApJ, 772, 32 Eiroa et al. 2011

05/28/13

Standard model for a debris disc

•  Radiation pressure blowout limit

•  Power law with slope 3-4 •  Peaks at larger sizes in the case

of lower stirring (blue curve) •  Similar effect if there is strong

grain transport (top to bottom) Protostars & Planets VI

•  Canonical model of narrow “birth ring”

•  Highly stirred discs produce halos

•  Halos are depressed quickly with decreased stirring

•  Strong transport means no halo Krivov et al. 2006; Thebault & Augereau 2007; Wyatt et al. 2011, review chapter & others 05/28/13

Asteroid belt analogues

•  Warm dust – Exozodiacal analogs – 1- several AU (habitable zone) – mid-IR, Spitzer, IRAS, WISE

•  ~1% of stars (or less) in any census

•  incidence is much lower than for cold dust

•  component now detectable with ALMA as well


ALMA 870 µm

HST 0.6 µm

Boley et al. 2012; Macgregor et al. 2012 05/28/13

See posters 2B065 (Ertel) 2B068 (Kennedy)

Warm dust statistics

10-4 10-3 10-2 10-1 100 101Fdisk/Fstar at 12µm

10-4

10-3

10-2

10-1

100

Frac

tion

> F d

isk/F

star a

t 12µ

m

WIS

E lim

it

~Sol

ar S

yste

m le

vel

~TPF

lim

itLB

TI li

mit

KIN

Observed distributionCombined model


Kennedy & Wyatt 2013

WISE data can detect bright exo-Zodis where the disk-to-star flux ratio is better than 0.1

LBTI will reach considerably fainter limits

Important for target selection for TPF

05/28/13

Vega and Fomalhaut

•  Both show evidence of an asteroid-belt analogue near the water-frost line

•  Location is not resolved but consistent with 14 AU (2’’ from Vega) for BB-like grains


IRS PACS

SMA

PACS

MIPS

ALMA

IRS

MSX IRTF

MSX

Su et al. 2013

05/28/13

Implication from the Structure of Vega’s Debris Disk Solar System

x 4

Vega System

face

-on

view

fa

ce-o

n vi

ew

b c

d e

face

-on

view

edge-on view

edge-on view

edge-on view

HR8799 System

Star Planets Debris HD20794 3x 2-5Mearth

Origin of low-mass ��planet-debris correlation?

If planets start at 8 AU then migrate in (Alibert et al. 2006), many planetesimals end up outside outermost planet in dynamically stable region (Payne et al. 2009)

The formation of a system with low-mass planets is also conducive to the formation of a debris disk that is bright after Gyr – why?

Exoplanet parameter space


10-2 10-1 100 101 102 103Semi-major axis (AU)

10-2

100

102

104

Min

imum

pla

net o

r dis

k m

ass (

MEa

rth)

M

V E

M

J

S

U N

AB

KB

Planets

Disks

Outer dust discs relative to the position of exoplanetary orbits

Disc masses are two orders of magnitude less than those typical of exoplanets

Recent work suggests discs may be dynamically important to stabilize or destabilize a disc (e.g. Moore & Quillen 2012 re: HR 8799; Raymond et al. 2012; Gomez et al. 2005) 05/28/13

Image from Mark Wyatt

Gas in debris discs

•  Most debris discs contain negligible amounts of gas

•  Beta Pic targeted for CO mapping with ALMA

•  CO rotation curve well detected

•  kinematic probe of debris discs may be possible

Protostars & Planets VI 05/28/13

Courtesy of Bill Dent See poster 2B067 (Moór)

Summary

•  Disc incidences well measured by Spitzer and

Herschel – Discs are at least as common around nearby stars as

planets •  Evidence of declining disc mass and fractional

luminosity over time •  Resolution of discs essential to understand

underlying structure •  Apparent correlation between low-mass planets

and debris discs •  ALMA is going to be awesome for debris disc

imaging Protostars & Planets VI 05/28/13

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Observations, Modeling and Theory of Debris Discs · 2013. 9. 9. · Eiroa et al. 2013 Sibthorpe et...

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