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High-resolution Imaging of Debris Disks Jane Greaves St Andrews University, Scotland why debris? why long λ? • debris is the ‘fallout’ of comet collisions – dust must be continually regenerated or will blow away, spiral into star... – shows that bodies at least km in size formed! • and are still there • sign that planets are likely? – comet belts define the outer edges of planetary systems • is the outer Solar System typical in size / content? • far-IR/submm observations pick up the thermal emission from cool dust grains – modelling the SED shows the grains are a few microns up to centimetres (or more) in size – temperatures tens of AU orbits – signal is optically thin • (so traces mass) – signal is >> the photosphere in submm progress • a lot of it, since excess found for Vega by IRAS! • now Spitzer... getting near Solar System dust level • imaging is key: – size scale of system – structure of cometary belt • planet perturbations! – holes cleared by planets rogues gallery τ Ceti ε Eridani Vega (α Lyr) Fomalhaut (α PsA) β Pic big discoveries • the Solar System is small – for 5 debris disks imaged around Sun-like stars: AU Mic (M1) ε Eri (K2) τ Ceti (G8) HD 107146 (G2) η Corvi (F2) • rout < 70 AU (submm) rout = 100 AU rout = 55 AU rout = 150 AU rout = 150 AU t ~ 0.01 Gyr t = 0.85 Gyr t = 10 Gyr t ~ 0.1 Gyr t ~ 1 Gyr was our history of planet formation affected by having a compact disk around the Sun? • the debris disk fraction may be high – ~50% for A stars – ~10% for F/G/K stars • some of which are older than the Sun! – but perhaps as many more cold disks? • submm detected • planning future surveys... • planets on very large orbits – e.g. at ~100 AU in Fomalhaut system? • ~3x orbit of Neptune story so far • every system looks different! • few are symmetrical! – high fraction of perturbing planets? • potential for unique method to detect distant planets • (unless you prefer decades of astrometry...) – ‘icy Neptunes’, not ‘hot Jupiters’ – high angular resolution very important • how it works: – dust of certain size trapped in resonances – identify clump patterns, e.g. 2:1, 3:2 ... • hence planet location – reality check: rotation of pattern 3:2 e = 0.3 e = 0.2 e = 0.1 really planet detection? • central holes might be argued away – grain sublimation...? (doesn’t quite work) • perturbed rings inexplicable without planet! – e.g. massive comet blow-ups too rare • modelling of dust trapping can be quite exact • radius, eccentricity, position + direction of orbit • minimum mass of planet • rotation of clump pattern is the clincher (this is not more indirect than radial velocity!) epsilon Eridani • nearest Solar-ish analogue – K2V star 3.2 pc away – but only 0.85 Gyr old • 5 years of SCUBA data • (by accident!) • well resolved ring ~ face-on – dust peaks 65 AU out – centre offset from star! • forced by inner gas giant? proper motion • star has moved 5’’ to right over 5 years – pick out real ring clumps...versus fixed high-z galaxies ring rotation • proper motion plus rotation leads to characteristic shifts – tentative!!!! • but systematic, ~2’’ counter-clockwise – if ok, planet at ~40 AU future plans Interferometers can... • pick out clumps precisely – and so the fraction of trapped dust, planet mass • detect rotation after much less time – 2’’ very hard with single dish! • boring waiting 5 years.... – quick with sub-arcsec resolution! SMA and ALMA • stars within 10 pc are great for SMA! – e.g. bright disks of Vega + Fomalhaut... 0.1’’ rotations per year • ALMA from ~2008 – great for fainter and more distant debris disks – also young disks... see a Jupiter in formation summary • debris disks give unique insight to planetary systems • imaging with high resolution is the key for use as a planet detection method • hence ground-based long-wavelength interferometers are the way of the future