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Pinpointing Planets in Circumstellar Disks Alice Quillen University of Rochester Mar 2009 3 Systems hosting disks with clearings Age Mass Type Distance Epsilon Eridani 1-2 0.5M CoKuTau4 140 pc Myr M Radius of clearing 10 AU Greaves et al. 97 Epislon Eridani 600 Myr 0.8M 3.2 pc K ~50 AU Fomalhaut 200 Myr 2.1M 7.7 pc A 133 AU Staplefeldt et al. Discovery Space All extrasolar planets discovered by radial velocity (blue dots), transit (red) and microlensing (yellow) to 31 August 2004. Also shows detection limits of forthcoming space- and ground-based instruments. Discovery space for planet detections based on disk/planet interactions More ambitiously in future Planets in disks • Young systems, evolution of early solar systems • Disk clearing by planets, Planet disk interactions Historical context for prediction of bodies prior to discovery: - Moonlet predicted in Enke gap from Voyager data (Cuzzi & Scargle ‘85), body then detected Showalter ’91 - Resonant ring in dust with Earth predicted (Jackson & Zook ‘89) then seen in IRAS data (Dermott et al. ‘94) - Neptune’s location predicted by Adams & LeVerrier (1845) then found by Galle (1846) Transition Disks Estimate of minimum planet mass to open a gap requires an estimate of disk viscosity. CoKuTau/4 D’Alessio et al. 05 4 AU 10 AU Wavelength μm Disk viscosity estimate either based on clearing timescale or using study of accretion disks. Mp > 0.1MJ Estimating required planet mass based on gap opening criterion • Limit on viscosity based on clearing during lifetime of object on a viscous timescale • Or base on estimates for accretion disks Minimum Gap Opening Planet In an Accretion Disk accretion, optically thick qmin M 0.48 0.8 M*0.42 L*0.08 Gapless disks lack planets Edgar et al. 07 CoKuTau4 is now known to be a binary star ➞ no planet required Kraus & Ireland 08 Extremely empty clearing explained via binary Are planets no longer required to explain disk clearing in young stellar objects? NO Massive disks exist with clearings that could not have been cleared by photo-evaporation (Alexander, Najita & Strom) Disks are seen in with large gaps, not just deep clearings as was CoKuTau4 --- these are best explained via planet formation and inefficient clearing Dust Capture models and Epsilon Eridani Debris Disk • Dust generated via collisions spirals inwards and is trapped in resonance with giant planets • Dust source is late stage collisional evolution – Debris Disks • Dust rings as signposts of planets Liou & Zook ‘99, Ozernoy et al. ‘01 • Vega disk model by Marc Kucher and collaborators • Exploring eccentric planet space, Deller & Maddison ‘05 • Rich History: Earth’s resonant ring Capture of drifting dust by meanmotion resonances with planets Signature of Giant planets seen in the Edgeworth-Kuiper Belt (Liou & Zook 1999) Dust integration weighted by lifetime shows that dust particles trapped in resonances dominate the distribution An early model for the dust ring in the Epsilon Eridani system Greaves et al.1997 Particles generated in resonance with an eccentric planet Long resonance lifetimes Different resonances contrived to make clumps Epsilon Eridani Recent developments Greaves et al. • Not all clumps are real • However clumps are rotating suggesting that there are some clumps in the disk in corotation with a planet • Possible 1 or two inner planets in central AU from Radial velocity and proper motion scatter Multiple component dust models based on Spitzer SED, imaging and IRS spectra infrared excess + model components Backman et al. 09 2 inner asteroid belts and one outer one Update on planet scenarios for Epsilon Eridani • Sticking planets right next to ring edges is moderately well justified • Our model for outer planet is vastly out of date, eccentric planet no longer needed • Collisions, migration, multiple planet interactions now key to understanding this system Lopsided disks, need for planets and the Pericenter glow model Fomalhaut Staplefeldt et al. • Based on asymmetry in asteroid distribution due to Jupiter’s forced eccentricity • Proposed to account for asymmetry of HR4796A’s disk (also has a clearing) by Mark Wyatt and collaborators HR4796A nicmos • Mass of planet is not constrained • Eccentricity and semi-major of planet related but not individually constrained Schneider et al. ‘99 HST image hailed as another signpost of a planetary system but nature of system was poorly constrained Another model Adam Deller and Sarah Maddison’s resonant capture model account for disk eccentricity but not sharp edge collisions ignored Kalas et al. 05 Fomalhaut’s eccentric ring • steep edge profile hz/r ~ 0.013 • eccentric e=0.11 • semi-major axis a=133AU • collision timescale =1000 orbits based on measured opacity at 24 microns • age 200 Myr • orbital period 1000yr Free and forced eccentricity efree eforced radii give you eccentricity If free eccentricity is zero then the object has the same eccentricity as the forced one ϖ longitude of pericenter Pericenter glow model • Collisions cause orbits to be near closed ones. This implies the free eccentricities in the ring are small. • The eccentricity of the ring is then the same as the forced eccentricity b3/2 2 ( ) a e forced 1 eplanet b3/ 2 ( ) ap • We require the edge of the disk to be truncated by the planet ~1 ering e forced eplanet • We consider models where eccentricity of ring and ring edge are both caused by the planet. Contrast with precessing ring models. Disk dynamical boundaries • For spiral density waves to be driven into a disk (work by Espresate and Lissauer) Collision time must be shorter than libration time Spiral density waves are not efficiently driven by a planet into Fomalhaut’s disk A different dynamical boundary is required • We consider accounting for the disk edge with the chaotic zone near corotation where there is a large change in dynamics • We require the removal timescale in the zone to exceed the collisional timescale. Corotation chaotic zone • Mean motion resonances get stronger and closer together near the planet’s corotation region. • An object in the overlap region can make close approaches to the planet • Width scales with planet mass to 2/7 power (Wisdom) Chaotic zone boundary N N D and removal within a a t collisionless lifetime removal Neptune size Saturn size What mass planet will clear out objects inside the chaos zone fast enough that collisions will not fill it in? Mp > Neptune Dynamics at low free eccentricity Expand about the fixed point (the zero free eccentricity orbit) H ( ; I , ) a 2 b cI same as for zero g I 1/ 2 cos( 0 eccentricity planet goes to zero near the planet ) ( g 01/f 2 g11/p 2 ) cos( p ) For particle eccentricity equal to the forced eccentricity and low free eccentricity, the corotation resonance cancels recover the 2/7 law, chaotic zone same width Velocity dispersion in the disk edge and an upper limit on Planet mass • Distance to disk edge set by width of chaos zone 2/ 7 da ~ 1.5 ue ~ 3/ 7 • Last resonance that doesn’t overlap the corotation zone affects velocity dispersion in the disk edge • Mp < Saturn Larger masses also would leave structure in ring, and it is featureless cleared out by perturbations from the planet Mp > Neptune Assume that the edge of the ring is the boundary of the chaotic zone. Planet can’t be too massive otherwise the edge of the ring would thicken or show structure Mp < Saturn nearly closed orbits due to collisions eccentricity of ring equal to that of the planet • Neptune < Mp < Saturn • Semi-major axis 119 AU (16’’ from star) location predicted using chaotic zone as boundary • Eccentricity ep~0.1, same as ring • Longitude of periastron same as the ring Multiple Epoch HST imaging reveals an object bound to the system Planet discovered at 115AU Interpretation rests on chaotic zone boundary periapse Kalas et al. 2008 Surprises Kalas et al 08 • Object is much much brighter than I predicted • Planet itself is not detected. • Object detected has colors of star and is ~60 times brighter in optical than a Jupiter mass planet • IR observations rule out planets more massive than 3 Jupiters • Circum-planetary disk to account for optical flux? • Mass of planet is not known. Eugene Chiang’s group suggest a larger planet than I predicted • Planet is slightly further away from disk edge than predicted using chaotic zone boundary. Eccentricity of planet and planet disk interaction still yet to be explained. Summary • 3 planets predicted – CokuTau4 planet ruled out – (but class of models still probably okay for other systems – Epsilon Eridani outer planet: model is missing key physics and so is out of date – Fomalhaut. Planet location pretty closely predicted • New models to create: with multiple planets to interpret disks with large gaps (as inferred from their spectral energy distribution), including HR8799 and Epislon Eridani post discovery view `Nice’ Model + Epoch of Late Heavy Bombardment Tsiganis et al. 05 • Disk of Fomalhaut is cold, not what would be seen for Solar system during epoch of Late Heavy Bombardment • Migration of planets in Fomalhaut system is likely Where is the next planet??