the ε Eridani debris disk Jane Greaves St Andrews, Scotland with Wayne Holland, Mark Wyatt & Bill Dent and cast of thousands...

discovery of the disk  nearest Solar type star with IRAS excess Aumann et al. 1985Aumann et al  only 7 nearby K-dwarfs even had their photospheres detected by IRAS at μm, at this stage Vega Fomalhaut β Pic

further photometry  far-IR SED extended to 200 μm with ISO  Habing et al. 1999, 2000; Walker & Heinrichsen 2000  mm photometry: why discrepancies? looking through a hole in a disk??looking through a hole in a disk??  missing ingredient was imaging Chini et al. 1990, 1991 Zuckerman & Becklin 1993 Weintraub & Stern 1994

why worry about it?  imaging the disk could be equivalent to a Solar System ‘time machine’ ‘late heavy bombardment’ environment of the Earth up to 0.75 Gyr‘late heavy bombardment’ environment of the Earth up to 0.75 Gyr... ε Eri is 0.85 Gyr old... ε Eri is 0.85 Gyr old  di Folco et al. 2004; VLTi stellar radius data image courtesy online Encyclopedia of Astrobiology Astronomy & Spaceflight

SCUBA observations  started Aug μm850 μm 450 μm (effectively from 2000)450 μm (effectively from 2000)  why SCUBA? first submillimetre camerafirst submillimetre camera resolution of 8-15”resolution of 8-15” to ~mJy-rmsto ~mJy-rms see Holland et al. 1999

from the start...  by night hour frame1 hour frame “another Solar System !? ” “another Solar System !? ”

first image  mystery solved! there really is an inner hole in a disk seen ~face-onthere really is an inner hole in a disk seen ~face-on cavity extends to ~Neptune’s orbitcavity extends to ~Neptune’s orbit but only half- cleared, so any exo-Earth likely to be massively bombardedbut only half- cleared, so any exo-Earth likely to be massively bombarded Greaves et al. 1998

major outcomes  really a dust disk  size ~ of Solar System radius of 65 AUradius of 65 AU  with large cleared cavity to ~ 30 AUto ~ 30 AU  inclination ~ tilt of stellar pole i ~ 25°i ~ 25°  ‘evolved’ dust, i.e. debris β ~ 1.0β ~ 1.0  LUMPS!

need for more  SCUBA upgrades in late > better 450 μm filter higher resolution view of clumpshigher resolution view of clumps better spectral index, temperature and massbetter spectral index, temperature and mass Sheret et al. 2004

images  at 850 μm clumps confirmedclumps confirmed Greaves et al. 2005

first results at 450  at 450 μm clumps similar to 850clumps similar to 850  independent data, different detectors  ~20 hours integration clump to west has 350 μm counterpart? (SHARC II)clump to west has 350 μm counterpart? (SHARC II)

planetary resonances?  dust caught in resonances with a planet forms characteristic patterns - > pinpoint planet location  why it’s hard in practice: eccentricity changes patternseccentricity changes patterns multiple resonances overlappingmultiple resonances overlapping 3:2 e = 0.3 e = 0.2 e = 0.1 Wyatt 2003; Kuchner & Holman 2003

interpretations Quillen & Thorndike 2002: 0.1 M Jup at a = 40 AU, e = 0.3 Ozernoy et al. 2000: 0.2 M Jup at a = 60 AU, e = 0

any hard evidence?  the inner planet: ~2 M Jup, a ~ 3.5 AU, e ~ 0.4~2 M Jup, a ~ 3.5 AU, e ~ 0.4  SCUBA: disk centre offset from star by ~1-2”by ~1-2” evidence of eccentricity forced on planetesimals?evidence of eccentricity forced on planetesimals?

an outer planet?  clearing and clumps seen all by one outer planet?all by one outer planet?  rotation expectations: period ~ years!period ~ years!  from just inside cavity, to embedded in dust ring but in a few years, high S/N clump centre should move by detectable amount (~arcsec)but in a few years, high S/N clump centre should move by detectable amount (~arcsec)

what’s really disk?  first submm proper motion experiment! background objects have not moved 4.5” with starbackground objects have not moved 4.5” with star 850 μm: colour, 1997/8 data contour, 2000/1/2 data

rotation?  tentative! but systematic patternbut systematic pattern proper motion plus rotation signature seenproper motion plus rotation signature seen  background blends are a problem

simulations  method: simulate a dust ring with clumps, for 15” beamsimulate a dust ring with clumps, for 15” beam add random noiseadd random noise add realistic background galaxy populationadd realistic background galaxy population  simulate SCUBA chopping on/off field-of-view produce ‘old’ and ‘new’ images, with known proper motion and chosen rotationproduce ‘old’ and ‘new’ images, with known proper motion and chosen rotation χ 2 -fitting to recover proper motion & rotationχ 2 -fitting to recover proper motion & rotation  simplifications:  circular, star-centred, face-on ring; point-like clumps

detecting rotation  scatter found in simulations is 5° (1σ) when no rotation includedwhen no rotation included  errors may differ with rotating clumps  χ 2 -fitting gives 11° for real 4.5-yr dataset ° error old/new example: 5° error

implications  if detected: planet at ~27 AU with ~150-yr periodplanet at ~27 AU with ~150-yr period  hence is both clearing and perturbing dust ring furthest-out exo-planet detection!furthest-out exo-planet detection!  still need to model resonances to identify: planet’s present position, mass, and orbital eccentricityplanet’s present position, mass, and orbital eccentricity

how to extend the technique  could be a major planet-finding tool, with higher resolutionhigher resolution  e.g. 1-month experiments for ALMA! more sensitivitymore sensitivity  ε Eri is close, and ~median mass of detected debris disks, for Sun-like stars  unique for distant planets?

discovery space  SCUBA-2 Legacy Survey JCMT, from 2007JCMT, from stars, to the 850 μm sub-mJy confusion limit500 stars, to the 850 μm sub-mJy confusion limit  Large Submm Telescope plans for ~ m-classplans for ~ m-class to 200 μm?to 200 μm? - > order of mag in resolution

summary  ε Eri is the nearest young-Solar System analogue history of cometary bombardmenthistory of cometary bombardment  demonstrates detection of outer planet perturbing cometary belt new robust method of using rotationnew robust method of using rotation