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Debris Disks around Nearby Stars

Debris Disks around Nearby Stars. David J. Wilner (Harvard-Smithsonian CfA ). What are Debris Disks? dust requires replenishment Interest in Resolved Morphologies holes, blobs as planet signatures Imaging Examples: Vega, e Eridani, Fomalhaut, ... Future Prospects

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Debris Disks around Nearby Stars

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  1. Debris Disks around Nearby Stars David J. Wilner (Harvard-Smithsonian CfA) • What are Debris Disks?dust requires replenishment • Interest in Resolved Morphologies • holes, blobs as planet signatures • Imaging Examples:Vega, e Eridani, Fomalhaut, ... • Future Prospects • Spitzer Space Telescope, SMA, ALMA collaborators: M. Holman (CfA), C.D. Dowell (Caltech), M. Kuchner (Princeton) SUNY Stony Brook, April 14, 2004

  2. Introduction to Debris Disks • Vega infrared excess discovered • serendipitously during IRAS • calibration (Aumann et al. 1984) • thermal emission from cold dust • Orbiting dust particles subject to • gravity, wind/radiation pressure (ejection) • and Poynting-Roberston drag (inspiral to star) • tP-R = (400/b)(Mo/M*)(r/AU)2 yr << stellar age (~350 Myr) • dust particles must be replenished • other nearby Vega-excess stars found by IRAS include • b Pic, Fomalhaut, e Eri (the “Fantastic Four”) optical far-ir

  3. b Pic disk geometry confirmed by • images of visible scattered light • (Smith & Terrile 1984) • ISO 60 mm survey finds 14/84 nearby • main-sequence stars (17%) with • excess emission (Habing et al. 2001) • debris disks are cool (T<100 K), Kuiper Belt size (R>50 AU) • tenuous (L/L* ~ 10-5 to 10-2, M ~ Mmoon), gas poor • various analyses of IRAS and ISO databases show: - 100+ candidates resembling Fantastic Four in T, L/L* • - no strong dependence with stellar type (M, L*) • - dust may decline with age (gradually? abruptly?) • few x 100 Myr ~ Solar System heavy bombardment

  4. Stages of Disk Evolution/Planet Formation lFl l 1. embeddedprotostar 104-105 yr 2. HAe/Be Star 105-106 yr 3. transition phase ~107 yr 4. debris disk >> 107 yr Malfait et al. 1998

  5. Observational Probes of Disk Structure scattered light emitted light optical/near-ir mid-ir far-ir/submm < spatial resolution << temperature dependence <> contrast with star, dynamic range > b pic J band Coronagraph+ AO 850 mm: 14 arcsec beam

  6. HST/NICMOS Scattered Light: Gaps and Rings

  7. JCMT 850 mm SCUBA Images • First moderate resolution • submm images (14 arcsec) • of Fantastic Four show disk • and ring morphologies, • also emission peaks offset • from stellar photospheres • Submm emission hints • at sculpting by planets: cleared interior cavities, • persistent dust features

  8. Planet Detection Parameter Space Kepler mission

  9. What Creates the Dust Blobs? • background galaxies: unlikely given the source counts • dust generated in situ by collisions of large planetesimals: would have to be recent (disperse in ~10 to 100 orbital • periods) and likely rare (massive enough to release Mmoon) • dust directly associated with orbiting bodies, e.g. remnants of circumplanetary disks? • dust spiralling starward trapped in resonances with planet • (cf. zodiacal dust trapped by Earth, Dermott et al. 1994)

  10. Plutinos are in 3:2 Mean Motion Resonance with Neptune CfA Minor Planet Center Jewitt Kuiper Belt Page

  11. Dust in our Solar System from Afar (Liou & Zook 1999) • numerical simulations • suggest Solar System • would be recognized to • harbor at least two planets: • Neptune, Jupiter • note: Solar System dust • emission at 850 mm at • 10 pc only ~ 1 mJy • (<< solar photosphere) Face-on view of the brightness from a numerical simulation of the column density of 23 mm dust particles from Liou & Zook (1999). The signatures of the planets are (1) deviation from a monotonic radial brightness profile, (2) ring along Neptune orbit, (3) variation along ring, (4) relative lack of particles within 10 AU

  12. Trapping by a low M, low e Planet • for Neptune, Earth: first order resonances • substantial trapping • example: 3:2 • each orbit has j=3 • longitudes of libration • for trapped particle (a) Several particle orbits with different w’s (longitudes of pericenter). (b) Libration centers of the 3jl-2lo-w term for two of these orbits. (c) Locus of all libration centers. (d) The density wave follows the motion of the planet at the same angular frequency as the planet.

  13. Structure in the Vega System (Wilner et al., ApJ, 569, L115) • Vega (a Lyrae): A0V main sequence star, d=7.76 pc • system viewed nearly pole-on: vsini, reddening • JCMT 850 mm SCUBA image • (Holland et al. 1998) shows: - roughly circular boundary • - an offset emission peak • - asymmetry extended NE-SW • - central cavity around the star • interferometry allows imaging • with factor > 10x higher angular • resolution; need high sensitivity see Koerner et al. 2001 for OVRO study

  14. IRAM PdBI Observations • compact D config • baselines 15-80 m • dry winter weather • 4 tracks : tint = 23 h • l=1.3 mm • + 3.3 mm • simultaneously • rms: ~0.3 mJy at 1.3 mm, ~0.1 mJy at 3.3 mm

  15. Images of Vega at l=1.3 mm 2.8 x 2.1 arcsec stellar photosphere 5.3x4.6 arcsec and dust blobs (low surface brightness)

  16. Trapping by a high M, high e Planet • presence of two peaks • different separations • of peaks from star • peaks not co-linear • with star • patterns from different • principle resonances • occur at same longitude, • 3:1, 4:1, 5:1, ... Libration centers of the 3l -lo-wo-w term. (a) Several particle orbits with different e and w. (b) The libration centers of two of these orbits when the planet is at pericenter. (c) All the libration centers. (d) Clumps formed by particles trapped in this term appear to rotate at half the angular frequency of the planet.

  17. Modeling the Millimeter Emission (left) A representative numerical simulation of 1.3mm dust emission from orbital dynamics that includes a Jupiter mass planet, radiation pressure, and P-R drag. The dust becomes temporarily entrained in mean motion resonances associated with the planet, producing a two-lobed structure. (right) Simulated observation of the numerical model, taking account the IRAM PdBI response for the Vega observations, and the IRAM PdBI image after subtraction of the stellar photosphere.

  18. Vega Summary

  19. Searching for Light from the Planet (Metchev et al. 2002) (left) Composite H band mosaic of Vega region obtained with PALAO. Eight point sources are detected. (right) H band sensitivity of the deep images to faint objects as a function or radial distance from Vega (analyzed for the east field). Solid points represent individual measurements; the solid line delineates the azimuthal average. The area between the vertical dotted lines indicates the locus of the inferred planet.

  20. Searching for Light from the Planet (Macintosh et al. 2003) (left) Deep Keck NIRC2 K’ band image of Vega. All candidate companions are in this field. The dashed circle indicates a radius of 15 arcsec. (right) 5s sensitivity of the image. The dashed lines indicate the planet masses from the models of Burrows et al. (1997).

  21. Is Vega like the Early Solar System? • Thommes et al. (1999) • +Thommes et al. (2002) • suggested Neptune • was scattered into a • highly eccentric orbit • Malhotra (1995) • suggested Neptune • migrated (outwards) by • 7 to 8 AU in ~10 Myr; • see Wyatt (2003) for • Vega model varient Neptune? aphelion perihelion Uranus? Saturn? Jupiter? The temporal evolution of one of Thommes et al.’s simulations of an unstable Jupiter-Core-Core-Saturn system. Shown are the semi-major axes (thick solid) as well as the instantaneous perihelion and aphelion distances ofthe orbits.

  22. The e Eri Debris Disk • single K2V star, age 0.5-1.0 Gyr, d=3.22 pc (3rd closest naked eye star), closest analog to young Solar System • (controversial) ~ 1 MJup radial velocity/astrometric planet, a=3.4 AU, e=0.6 (Hatzes et al. 2000) • far-ir spectrum fit by r~60 AU ring-like disk (Dent et al. 2000, Li et al. 2003, Sheret et al. 2003 Moran et al. 2004)

  23. Structure in the e Eri System • JCMT 850 mm SCUBA image shows nearly face-on ~60 AU • radius ring with azimuthal variations (Greaves et al. 1999) • Structure due to a • planetary perturber? • Liou et al. 1999, • Ozernoy et al. 2000 • Quillen & Thorndike 2002 Inner Peak?

  24. Potential of Inner Dust Imaging • interaction of • inspiralling dust • with eccentric • planet should • produce two dust • peaks, like the • Vega system • follow motions of • dust peaks • to independently • characterize planet

  25. 350 mm Observations with SHARC II • SHARC II: Caltech Submillimeter Observatory facility camera, 12x32 filled array of ‘pop-up’ bolometers, optimized for 350 mm (9 arcsec beam) • Observations made in Jan 2003 commissioning run, • >16 hours on e Eridani in excellent weather (t225<0.037), image rms ~3 mJy

  26. Image of e Eri at l=350 mm Image of e Eri at l=350 mm

  27. 350 mm Imaging Results • confirm basic ~ 60 AU ring structure • no evidence forcentral rise in flux density corresponding to inner “zodiacal” component; central clearing bolsters planetscenario • clumpy structure of ring resolved into two (nearly) symmetric arcuate features, brightest se and nw • clumps outside ring consistent with background of high redshift galaxies >10 mJy ~1 arcmin-2 (Smail et al. 2002)

  28. Signpost of Planet Formation • bright (L~ 10-4 L*) narrow (Da/a ~ 0.1) ring of observed size explained by collisional cascade in planetesimal disk stirred by recent formation of bodies of radius >1000 km • does not account for azimuthal variations (Kenyon & Bromley 2002, 2004)

  29. Sculpting by a Planet? • characterization of possible unseen planets requires matching robust features using numerical simulations 0.2 MJup e = 0 2:1, 3:2 w/ high libration < 0.3 MJup e ~ 0.3 5:3, 3:2 w/ phase segregation Ozernoy et al. 2000 Quillen & Thorndike 2002 • models that selectively populate particular resonances are not realistic unless additional factors invoked, e.g. parent bodies trapped by planet migration, encounter

  30. Comments on Models • structure depends on many parameters, e.g. planet mass, eccentricity, semi-major axis, orbital phase, inclination, dust properties, orbits of parent bodies • prominent “two-blob”morphology, like Vega, Jupiter mass planet in eccentric orbit traps dust in exterior principal mean motion resonances • models have time dependence that can be tested by synoptic observations with sufficient sensitivity and angular resolution (submm interferometry)

  31. The Closest (< 4 pc) F,G,K Stars Procyon binary 61 Cyg binary e Eri 0.01 ME Sun <0.0001 ME a Cen multiple t Ceti 0.0005 ME e Ind multiple

  32. Future Prospects • Spitzer: high sensitivity at far-infrared wavelengths not • accessible from the ground will provide exquisite SEDs • for a large sample and greatly improve statistics Riecke GTO Projects, FEPS Legacy Project M. Meyer

  33. First Results from Spitzer Fomalhaut

  34. Young Solar Analog Debris Disk • HD107146, G2V, distance 28.5 pc, age ~100 Myr • discovered during ground based support for Legacy • Project “Formation and Evolution of Planetary Systems” undetected by IRAS at 25 mm (Williams et al. 2004) • substantial population of cold disks, see Wyatt et al. (2003)

  35. Submillimeter Array: a collaborative project of the Smithsonian • Astrophysical Observatory and the Academia Sinica (Taiwan), • eight 6 meter diameter antennas on Mauna Kea for arcsecond • imaging initially for 1300, 850, 450 mm atmospheric windows • submm interferometry is challenging • official SMA dedication was November 22, 2003 • look for first call for external proposals in mid-2004

  36. Early SMA Images Mars Atmosphere CO(2-1) (Gurwell) TW Hya CO(3-2) Keplerian Disk (Qi et al. 2004)

  37. ALMA: large array (64 x 12 m + 12 x 7 m) • North America, Europe, and likely Japan • high sensitivity, high resolution (10 mas) full operation in 2012? • best possible site, Atacama at 5000 m, large bandwidth, • high fidelity imaging, active compensation for atmosphere

  38. Debris Disks around Nearby Stars • What are Debris Disks?dust requires replenishment • Resolved Morphologies • holes, blobs as planet • signatures • Imaging Examples dust structureplausibly due • to resonances with planet • Future Prospects • Spitzer, SMA, ALMA

  39. Dust can outshine Terrestrial Planets Dust clumps in the zodiacal cloud from 10 pc: (a) Model of the brightest unresolved clump from collisions in the asteroid belt; the horizontal line indicates the flux from an Earth, the vertical line represents the beam size; (b) Model of the Earth’s resonant ring (Dermott et al. 1994) at 10 mm with a 0.06 arcsec beam. The Earth’s emission would be at [+0.1,0] and would be 10 to 20 times brighter than the bright trailing clump in the ring (Wyatt 2001).

  40. Spectral Energy Distributions of Excess • ISO 25 mm survey of nearby • main-sequence stars shows • that warm disks are rare • (Laureijs et al. 2002). • [25/60] impies T<120 K • evacuated inner regions • are common features of • debris disk systems

  41. Zodiacal Light Clementine 1994

  42. Fomalhaut: a Nearly Uniform Ring (Holland et al. 2002) • residuals reveal a “clump” with 5% of total flux SCUBA 450 mm images of the Fomalhaut disk (from Holland et al. 2002): (a) observation, (b) axisymmetric smooth disk model, and (c) the residuals, which show that the asymmetry could be explained by a clump embedded in a smooth disk. All contours are spaced at 1s = 13 mJy/beam. The dashed white oval in (b) shows the inner edge of the mid-plane of the disk, a 125 AU radius ring inclined 20 degrees to the line of sight. The stellar photosphere has been subtracted.

  43. JCMT 850 mm SCUBA Images 100 AU 19.3 pc 7.7 pc 7.8 pc 3.2 pc

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