The Architecture of Planetary Systems Revealed by Debris Disk Imaging

The architecture of planetary systems revealed by debris disk imaging

Paul Kalas University of California at Berkeley Collaborators: James Graham, Mark Clampin, Brenda Matthews, Mike Fitzgerald, Geoff Bower, Eugene Chiang, et al.

Outline 1. Show the rapid progress of debris disk imaging. 2. Present new HST polarization results for AU Mic. 3. Discuss Fomalhaut’s Belt and evidence for a planetary system. 4. Review more disks and suggest some ideas regarding the origin of their architecture.

Kalas et al. 2004

Voyager 2 reaches Saturn (1981)

Bernard Lyot (1897-1952) Brad Smith (head of Voyager imaging team)

Direct Image of the β Pic Dust Disk as early as 1983

Smith & Terrile 1984

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

β Pic

Vega

Fomalhaut 1998 see http://www.disksite.com ε Eri

HR 4796A

HD 141569 Resolved images of dust structure linked to unseen planets

AU Mic (GJ803): Early evidence for circumstellar dust:

Tsikoudi 1988, "Flare stars detected by the Infrared Astronomical Satellite" Mathioudakis & Doyle 1991, "Active M-type stars from the ultraviolet to the infrared"

One of the closest flare stars: Distance = 9.9 pc SpT = M1Ve

Mass = 0.5 Msun Radius = 0.56 Rsun Teff = 3500 K Luminosity = 0.1 Lsun Mv = 8.8 mag Period = 4.865 d Avg. Mag. Field: B = 4000 G Ha Equivalent Width = 8.70 Quiescient X-ray flux:

log10 (Lx) = 29.8 erg/s Age: Young

beta Pic Moving Group

Kalas & Deltorn (1999, unpublished) Barrado y Nav ascues 1999

Zuckerman, Song, et al. 2001

AU Mic Discovery Image: Kalas, Liu, & Matthews 2004

R-band, UH 2.2 m telescope, 0.4"/pix, 900 s, seeing FWHM = 1.1"

Metchev et al. 2005 (Keck NIR), Krist et al. 2005 (HST, visible), Liu 2004 (Keck, NIR)

• Radius: 7.5 - 150 AU • Width: 2.5 - 3.5 AU within 50 AU • Dust depletion beyond the ice sublimation boundary • Blue scattering throughout the disk

Krist et al. 2005

Origin of the Disk: Grain lifetimes as a function of radius

from Backman & Paresce 1993: Kalas et al. 2004 Poynting-Robertson Drag Timescale

Collision Timescale

Sublimation Timescale

Most of the grains seen in the discovery image are fragments of larger objects, very little mass <67 AU: 0.1 mm grains have spiraled into the star in 8 Myr has been removed from the <20 AU: 1.0 mm grains have spiraled into the star in 8 Myr system. 100 AU: Collision timescale is 1.8 Myr >200 AU:Collisionally unevolved disk, pristine material Cambridge Planet-Dis k Connection Paul Kalas © 2006 AU Mic Origin of the Disk? Plavchan, Jura, & Lipscy 2005 Augereau et al. 2006 (in press)

radiation pressure / gravity stellar wind / gravity

100 x solar mass loss rate

projected radius

Kalas et al. 2004

F606W ACS/HRC

Simultaneous fit to optical SB profile and polarization

Need high p, and large g. inner radius ~40 AU, outer radius ~200 AU. Small grains give high p, but scatter too If astronomical isotropically. silicates, P = 94 ± 6%

If ice, P = 91 ± 9%

Cambridge Planet-Disk Connection Paul Kalas © 2006 Is this what we see around AU Mic? No, comet grains have porosity ~70% after sublimation of volatiles. Moreover, AU Mic grains originate far beyond the ice sublimation radius.

More likely, particle coagulation via ballistic cluster- cluster aggregation.

To avoid restructuring and compactification, the upper size limit of the parent bodies is ~10 cm.

Wurm & Blum 1998

How does AU Mic compare to Beta Pic?

Artymowicz 1997

J, H, K

Two component model disk (Mie scattering, Monte Carlo radiative transfer code; Duchene et al). Polarization

Compact silicates (Drain & Li 2001) do not work. V-band (HST) Mathis & Whiffen (1989) model works well. Highly porous aggregates of silicates, carbonaceous and icy elements. H-band (Keck)

Polarization too high in this simple model. Non- spherical grains? Minimum grain size varies Fitzgerald et al. 2006 with radius?

Stapelfeldt et al. 2004 ring eccentricity in model = 0.07 planet orbit: a = 40 AU, e = 0.15

Marsh et al. 2005 Model fit using Spitzer (24, 70, 160 µm) & 350 µm image suggests 8 AU center of symmetry offset.

Fomalhaut • Semi-major axis: a =140.7± 1.8 AU • Semi-minor axis: b = 57.5 ± 0.7 AU Kalas, Graham & Clampin • PA major axis: 156.0˚±0.3˚ 2005, Nature, Vol. 435, pp. 1067 • Inclination: i = 65.9˚± 0.4˚ • Projected Offset: 13.4 ± 1 AU F814W: 80 min., 17 May, 02 Aug, 27 Oct, 2004 • PA of offset: 156.0˚ ± 0.3˚ F606W: 45 min., 27 Oct. 2004 • Deprojected Offset f = 15.3 AU 25 mas / pix, FWHM = 60 mas = 0.5 AU • Eccentricity: e = f / a = 0.11 orbital period at 140 AU = 1200 yr

Asymmetric Scattering Phase Function Kalas, Graham & Clampin 2006

|g| = 0.2

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

Integrated light from model gives a total grain scattering cross section of 8.7 x 1025 cm2.

Assume 30 mm sized particles and density 2.5 g cm-2, albedo = 0.1, then belt mass is 0.09 Lunar mass --> 17 times smaller than inferred from sub- mm data. Albedo may be much lower --> a dark belt similar to the rings of Uranus.

Evidence for a planetary system: Center of symmetry offset Kalas, Graham & Clampin 2006 Wyatt et al. 1999 G. Schneider, STIS

How Observ ations of circumstellar disk asymmetries can rev eal hidden planets:Pericenter glow and its application to the HR 4796A disk Wyatt, M.C. et al. 1999, ApJ, 527, 918

• Particle eccentricity composed of a p rop er (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. S = stellar position 1998). D = center of particle orbit • External eccentric perturber can produce the same center of C = center of precession circle symmetry offset, but not the sharp inner disk boundary. P = pericenter of a particle orbit DP = a, semi-major axis of a particle orbit

wf = direction of forced pericenter SD = a e SC = a eforced CD = a eproper Torus inner radius = a (1 - eproper) = 133 AU Torus outer radius = a (1+ eproper) Cambridge Planet-Disk Connection Paul Kalas © 2006 Kalas, Graham & Clampin 2006 Radial cut along 10˚ segement Q2 (apastron), in the illumination corrected image; cut traces the material surface density of the structure rather than its brightness.

Model has a hard edge inner edge, but the integration in the line of sight and the 7 AU vertical scale height means that the edge will not appear sharp in the sky projection.

Quillen (2006) argues that the steepness of the edge is consistent with a Neptune to Saturn-mass object at 119 AU semi-major axis.

radial cuts

planets

1) Dust produced by KBOs no planets a=35-50 AU, i = 0˚-17˚ 2) 1-40 mm, r = 2.7 g cm-3 & 3-120 mm, r =1 g cm-3 3) 7 planet, or no planets 4) Solar gravity, RP, P-R drag, solar wind drag. 5) b = RP / gravity ∝

L* / r s

HD 139664 HD 107146 HD 53143 HD 92945 SpT=F5V SpT=G2V SpT=K1V SpT=K1V d=17.5 pc d=28.5 pc d=18.4 pc d = 22 pc age = 300 Myr age = 100 Myr age = 1.0 Gyr age = 100 Myr 60 - 109 AU 60 - 185 AU >110 AU >146 AU Kalas et al. 2006 Ardila et al. 2004 Kalas et al. 2006 Clampin et al. 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?