FOMALHAUTReview and evidence for a planetary system

FOMALHAUTReview and evidence for a planetary system

Paul KalasUniversity of California at Berkeley

with support from

NSF Center for Adaptive Optics

NASA Origins Program

STScI/AURA GO-9475, GO-9861, GO-9862, GO-10228

kalas (at) astron.berkeley.eduhttp://astron.berkeley.edu/~kalas

An early observation of a debris diskAn early observation of a debris disk

"The light at its brightest was considerably fainter than the brighterportions of the milky way... The outline generally appeared of a parabolic or probably elliptical form, and it would seem excentricas regards the sun, and also inclined, though but slightly to the ecliptic."

-- Captain Jacob 1859

Introduction: Vega Phenomenon

Leinert & Gruen 1990

Thermal IR excess from Zodiacal dust cloud

Introduction: Vega Phenomenon

~150 K

The Vega PhenomenonThe discovery of excess emission from main sequence stars at IRAS wavelengths

(Aumann et al. 1984).

The Vega PhenomenonThe discovery of excess emission from main sequence stars at IRAS wavelengths

(Aumann et al. 1984).

Introduction: Vega Phenomenon

Backman & Paresce 1993"The Big Three"

Direct Image of Pic Dust Diskas early as 1983

Direct Image of Pic Dust Diskas early as 1983

Smith & Terrile 1984

Introduction: Vega Phenomenon

Beta Pic was the Rosetta Stone Debris Disk for 15 years>300 refereed papers

And how about Fomalhaut?Optical ground-based coronagraphy

No detection.

Kalas & Jewitt 1996

Pic would remain the flagship debris disk for 14 years

ReplenishmentAge of system >> lifetime of dust

ReplenishmentAge of system >> lifetime of dust

Artymowicz 1997

Pic

Introduction: Vega Phenomenon

Artymowicz 1997(Also applicable to Fomalhaut)

0.5 m 2.2 m 10-20 m 850 m

Pic

Vega

Fomalhaut

Eri

HR 4796A

HD 141569

Introduction: Vega Phenomenon

Resolved images of duststructure linked to unseen planets

glow

Structure: Effects of unseen planets Structure: Effects of unseen planets

Dermott et al. 1994resonant trapping by Earth

Rings & Blobs(Zody & KB)

Holes(most common)

VerticalWarps( Pic)

Mouillet et al. 1997secular perturbation in beta Pic

Roques et al. 1994resonant trapping and ejection

Disk Holes = Planet Formation?(Ozernoy et al. 2000)

Disk Holes = Planet Formation?(Ozernoy et al. 2000)

850 mData

Links: Structure

Planet+dustSimulation

2 MJ at 50-60 AUlow eccentricity

Vega eps Eri

2 MJ

0.2 MJ

FOMALHAUT: IRAS (1984-1990)Extended at 60 microns

Backman & Paresce 1993

36" source diameter, ~30 micron grains, Tmax~75 K

FOMALHAUT: JCMT at 800 microns (1993)

Zuckerman & Becklin (1993)

Extended north-south, PA = 0˚ ± 30˚

FOMALHAUT: Sub-mm (1998)Holland, Greaves, Zuckerman et al. 1998

see also Dent et al. (2000)for modeling and analysis

SED FittingT = 40 Ka = 100 m dominanta = 10 m < 10% of totalMdust = 1.4 - 1.5 lunar

Image FittingA belt, 100-140 AU radiusSharp outer cutoffcollision=2x105 yr at 100 AU

Discovery of 2 peaks~10” radius (77 AU)60 AU radius cavity

FOMALHAUT: AgeBarrado y Navascues et al. 1997, 1998

Gliese (1969) suggested that Fomalhaut and Gl 879 (K5Ve) are a physical pair.

Castor Moving Group

Search for debris disks around AU Mic

AU Microscopii - PastCircumstellar Properties

QuickTime™ and aGIF decompressor

are needed to see this picture.

Deltorn & Kalas, unpublished.

FOMALHAUT: AgeAge = age of Gl 879 = 200 ± 100 Myr

Isochrones at 3, 10, 35, 70 Myr and ZAMSBarrado y Navascues et al. 1997, 1998

FOMALHAUT: AgeBetween a Pic and a Kuiper Belt

Adapted from Zuckerman 2001 (ARAA)

Dust abundance vs. age

FOMALHAUT: Revisited at 450 & 850 microns

A non-uniform ring

Holland et al. 2003; also Wyatt & Dent 2002

FOMALHAUT: Inner arc or clump?3 detection, 100 AU from star, 50 AU in length

Model belt: 125-185 AU, peak at 135 AUFlux from arc is 5% of total, ~0.075 lunar massOffset ring or pericenter glow cannot fit the asymmetryInstead, centered ring, but asymmetric density from 1:1 MMR

Holland et al. 2003; also Wyatt & Dent 2002

FOMALHAUT: Spitzer

spatially resolved at 24, 70 & 160 m

Stapelfeldt et al. 2004

FOMALHAUT: SpitzerStapelfeldt et al. 2004

ring eccentricity in model = 0.07planet orbit: a = 40 AU, e = 0.15

160

70 24

FOMALHAUT: 350 m + SpitzerMarsh et al. 2005

69 AU resolution at 350 micronRing with no inner clumpT = 42 K

Model fit using Spitzer (24, 70, 160 m) & 350 m image suggests 8 AU center of symmetry offset.

Planet a = 86 AU, e = 0.07, M > 1 Earth if the inner ring boundary is the location of a 2:3 MMR (Neptune :CKB)

HST/ACS Search for Planets"ACS detection of sub-stellar companions around Vega, Fomalhaut and Beta Pic via parallax &

proper motion"Cycle 12 GO Program: Kalas, Graham & Clampin

HST/ACS Search for Planets"ACS detection of sub-stellar companions around Vega, Fomalhaut and Beta Pic via parallax &

proper motion"Cycle 12 GO Program: Kalas, Graham & Clampin

Co-moving companions are detectable within a few months using the ACS/HRC (25 mas/pixel, FWHM = 60 mas).

The existence of planets is inferred from disk structure observed in the sub-mm

With age ~200 Myr and distance ~7.7 pc, thermal flux from cooling Jupiters and brown dwarfs may be detected in the HRC F814W broadband filter (I-band). F814W = 26 mag for 1 Jupiter mass. F814W = 22 mag for 10 Jupiter mass

Fomalhaut Field Source

May 17 - Sep. 27, 2004I = 23.5 mag

Fomalhaut Optical Discovery

HST ACS planet search

Hubble Space Telescope

JCMT SCUBA 450 micron map (Wyatt & Dent 2002)

HST Fomalhaut detection -- consistent with sub-mm maps

HST ACS planet search

Fomalhaut

F814W: 80 min., 17 May, 02 Aug, 27 Oct, 2004F606W: 45 min., 27 Oct. 200425 mas / pix, FWHM = 60 mas = 0.5 AU

Kalas, Graham & Clampin2005, Nature, Vol. 435, pp. 1067

• Semi-major axis: a =140.7± 1.8 AU• Semi-minor axis: b = 57.5 ± 0.7 AU• PA major axis: 156.0˚±0.3˚• Inclination: i = 65.9˚± 0.4˚• Projected Offset: 13.4 ± 1 AU• PA of offset: 156.0˚ ± 0.3˚• Deprojected Offset f = 15.3 AU• Eccentricity: e = f / a = 0.11

orbital period at 140 AU = 1200 yr

No inner clumps

HST ACS planet search

Model Disk Fitting

• inner & outer radius• inclination to line of sight• scattering phase function

Grain number density function of radius and height

HST ACS planet search

Asymmetric Scattering Phase Function

|g| = 0.2

Zodiacal Light = +0.2; Forward ScatteringMedian size ~30 microns (blowout size for Fomalhaut is 7 microns).

Model subtraction emphasizes inner dust component.1-2 mag fainter than Q3. SE is 1.7 times brighter than NW.

Inner dust component also detected in thermal infrared by Holland et al. 2003 and Stapelfeldt et al. 2004.

HST ACS planet search

Belt width as a function of azimuth

caveat the missing information: 1) Fomalhaut's belt is narrowest near apastron2) No clear evidence for azimuthal structure

Circular annulus with inner radius 133 AU, outer annulus 158 AU

HST ACS planet search

Radial cut along 10˚ segment Q2 (apastron), in the illumination corrected image; cut traces the material surface density of the structure rather than its brightness.

Cuts were actually made in 2˚ increments such that we show the mean value and the error bars are the standard deviation per measurement. Thus the error bars indicate the degree of azimuthal noise, whereas the overall modulation of points radially indicates the radial noise.

Blue line is the model fit:

1) Knife-edge inner edge = 133 AU

2) n(r) = n(ro) r -9

3) Scale height = 3.5 AU at 133 AU

Evidence for a planetary system: Knife-edge inner boundary

Evidence for planets: sharp inner edgesKuiper Belt dust models by Moro-Martin & Malhotra 2002

1) Dust produced by KBOs

a=35-50 AU, i = 0˚-17˚

2) 1-40 m, = 2.7 g cm-3 &

3-120 m, =1 g cm-3

3) 7 planet, or no planets

4) Solar gravity, RP, P-R

drag, solar wind drag.

5) = RP / gravity

L* / s

radial cuts

no planets

planets

HST ACS planet search

Wyatt et al. 1999

How Observations of circumstellar disk asymmetries can reveal hidden planets:Pericenter glow and its application to the HR 4796A diskWyatt, M.C. et al. 1999, ApJ, 527, 918

• Particle eccentricity composed of a proper (or free) eccentricity, inherent to the particle, and a forced eccentricity due to a perturber. The pericenter also has a free and a forced component.

• The orbital distribution of particles with common forced elements will be a torus with center, C, offset from the stellar position, S.

• The forcing is due to an eccentric companion that could be either inside or outside the belt.

• Infer offset 2 AU for HR 4796A

• Similarly offset = 0.01 AU for Zodiacal dust disk (e.g. Kelsall et al. 1998).

• External eccentric perturber can produce the same center of symmetry offset, but not the sharp inner disk boundary.

S = stellar positionD = center of particle orbitC = center of precession circleP = pericenter of a particle orbitDP = a, semi-major axis of a particle orbitwf = direction of forced pericenterSD = a e SC = a eforced CD = a eproper

Torus inner radius = a (1 - eproper) = 133 AUTorus outer radius = a (1+ eproper)

G. Schneider, STIS

Evidence for a planetary system: Center of symmetry offset

HST ACS planet search

QuickTime™ and aGIF decompressor

are needed to see this picture.

Fomalhaut Simulation

Adam Deller & Sarah Maddison(Swinburne University of Technology)

Planet Mass = 2 M_jupitereccentricity = 0.3semi-major axis = 70 AU

Architectures

Planetary System Architectures: Solar System vs. Fomalhaut

Kuiper Belt: 30 - 50 AU Sedna: Perihelion = 76 AU, Aphelion = 990 AU

Fomalhaut & the Kuiper Belt: A fairy tale1. Truncation of disk by OB stellar

radiation or dynamical perturbations in early star forming environment (make the outer edge first).

2. Disk heating and mass loss lead to an unstable system.

3. Unstable systems lead to giant planet migration with larger eccentricities than found in dynamically cold (e=0.001) and massive disks.

4. Outward planet migration stops when disk material runs out, but will continue in more massive disks (makes the large inner edge).

Larwood & Kalas 2001

Tsiganis et al. 2005

Architectures: Physical extent

beta Pic

AU Mic

Fomalhaut

HR 4796A

HD 107146

Sun

>>800 AU

200 AU

170 AU

160 AU

70 AU

50 AU

Disks placed at the same distance:

Introduction: Vega Phenomenon

HST ACS planet search

Fomalhaut's Belt: Significance to Astronomy1. Fomalhaut's belt is the closest that has been resolved in scattered light.

2. Inclination 66˚ means that it can be studied around its entire circumference

3. Belt characteristics that are consistent with planet-mass objects orbiting Fomalhaut:

1) The belt center is offset from the stellar center by 15 AU ± 1 AU, demanding

apsidal alignment by a planet,

2) Disk edges are sharper on the inner boundary compared to the outer boundary

and consistent with our scattered light model that simulates a knife-edge inner

boundary and dynamical models of planet-disk interactions.

1. Age 200-300 Myr, this is one of the oldest debris disk seen in scattered light. It is probably

leaving the clean-up phase and progressing to a configuration similar to that of our solar

system.

2. Replace Beta Pictoris as the debris

disk Rosetta Stone?

• Astrophysical Mirror to our

Kuiper Belt?

Summary Questions:

1. Outer extent of the disk?

2. Color? Main belt vs. inner dust?

3. Width as a function of azimuth?

4. Azimuthal asymmetries?

5. Plausible companion properties?

6. Planet at large radii?

7. Exterior companion?

8. Co-moving blobs?

Contact Info:Kalas (at) astron.berkeley.edu

More information:http://www.disksite.com/

Reference:Kalas et al. 2005, Nature, Vol. 435, pp. 1067

HST ACS planet search

Future HST/ACS Observations: Multi-color imaging of the entire belt in Cycle 14 (July - August 2006)

• Search for azimuthal asymmetries; e.g. Trojans

• Measure ring width as a function of azimuth

• Search for color gradients azimuthally and radially

• Characterize properties of Zodiacal dust analog; dust interior to the belt.

• Understand grain properties, source regions

More Future Work:

• Are there planets? Detect the planet(s) directly. Keck II AO run in July, October.

• Are there external perturbers confining the outer belt boundary? Wide field multi-epoch search.

• What is the origin of the belt? Planet formation theory; migration; resonance vs. ejection. What are the orbital elements of a planet?

• Is Fomalhaut's belt a mirror of our young Kuiper Belt? What accounts for the factor of three difference in semi-major axis scale?

HST ACS planet search

Future WorkElliot et al. 1981Uranus ring occultation