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the ε Eridani debris disk

Delve into the discovery and analysis of the debris disk around Epsilon Eridani, offering clues to our own Solar System's early history. Learn about the methodology, findings, and implications for exoplanet detection. This pioneering research sheds light on the dynamics of planetary formation and evolution in distant star systems.

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the ε Eridani debris disk

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

  2. β Pic Fomalhaut Vega discovery of the disk • nearest Solar type star with IRAS excess • Aumann et al. 1985 • only 7 nearby K-dwarfs even had their photospheres detected by IRAS at 12-60 μm, at this stage

  3. 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?? • missing ingredient was imaging Chini et al. 1990, 1991 Zuckerman & Becklin 1993 Weintraub & Stern 1994

  4. 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 • ... ε Eri is 0.85 Gyr old • di Folco et al. 2004; VLTi stellar radius data image courtesy online Encyclopedia of Astrobiology Astronomy & Spaceflight

  5. SCUBA observations • started Aug 1997 • 850 μm • 450 μm (effectively from 2000) • why SCUBA? • first submillimetre camera • resolution of 8-15” • to ~mJy-rms see Holland et al. 1999

  6. from the start... • by night 1.... • 1 hour frame “another Solar System !? ”

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

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

  9. need for more • SCUBA upgrades in late 1999 -> better 450 μm filter • higher resolution view of clumps • better spectral index, temperature and mass Sheret et al. 2004

  10. 1997-2002 images • at 850 μm • clumps confirmed Greaves et al. 2005

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

  12. 3:2 e = 0.3 e = 0.2 e = 0.1 planetary resonances? • dust caught in resonances with a planet forms characteristic patterns - > pinpoint planet location • why it’s hard in practice: • eccentricity changes patterns • multiple resonances overlapping Wyatt 2003; Kuchner & Holman 2003

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

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

  15. an outer planet? • clearing and clumps seen • all by one outer planet? • rotation expectations: • period ~ 180-570 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)

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

  17. rotation? • tentative! • but systematic pattern • proper motion plus rotation signature seen • background blends are a problem

  18. simulations • method: • simulate a dust ring with clumps, for 15” beam • add random noise • add realistic background galaxy population • simulate SCUBA chopping on/off field-of-view • produce ‘old’ and ‘new’ images, with known proper motion and chosen rotation • χ2-fitting to recover proper motion & rotation • simplifications: • circular, star-centred, face-on ring; point-like clumps

  19. detecting rotation • scatter found in simulations is 5° (1σ) • when no rotation included • errors may differ with rotating clumps • χ2-fitting gives 11° for real 4.5-yr dataset old/new example: 5° error

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

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

  22. discovery space • SCUBA-2 Legacy Survey • JCMT, from 2007 • 500 stars, to the 850 μm sub-mJy confusion limit • Large Submm Telescope • plans for ~30-100 m-class • to 200 μm? - > order of mag in resolution

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

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