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)r out < 70 AU (submm)t ~ 0.01 Gyr ε Eri (K2)r out = 100 AUt = 0.85 Gyr τ Ceti (G8)r out = 55 AUt = 10 Gyr HD (G2)r out = 150 AU t ~ 0.1 Gyr η Corvi (F2)r out = 150 AUt ~ 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