the ε eridani debris disk jane greaves st andrews, scotland with wayne holland, mark wyatt &...
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the the εε Eridani debris diskEridani debris disk
Jane GreavesJane GreavesSt Andrews, ScotlandSt Andrews, Scotland
with Wayne Holland, Mark Wyatt & Bill Dentwith Wayne Holland, Mark Wyatt & Bill Dentand cast of thousands...and cast of thousands...
discovery of the diskdiscovery of the disk nearest nearest SolarSolar type star with IRAS excess type star with IRAS excess
• Aumann et al. 1985Aumann et al. 1985 only 7 nearby K-dwarfs even had their photospheres only 7 nearby K-dwarfs even had their photospheres
detected by IRAS at 12-60 detected by IRAS at 12-60 μμm, at this stagem, at this stage
Vega
Fomalhaut
β Pic
further photometryfurther photometry
far-IR SED extended to 200 far-IR SED extended to 200 μμm with ISOm with ISO Habing et al. 1999, 2000; Walker & Heinrichsen 2000Habing et al. 1999, 2000; Walker & Heinrichsen 2000
mm photometry: why discrepancies?mm photometry: why discrepancies?• looking through a hole in a disk??looking through a hole in a disk??
missing ingredient was missing ingredient was imagingimaging
Chini et al. 1990, 1991Zuckerman & Becklin 1993Weintraub & Stern 1994
why worry about it?why worry about it? imaging the disk could be equivalent to a imaging the disk could be equivalent to a
Solar System ‘time machine’Solar System ‘time machine’
• ‘‘late heavy bombardment’ late heavy bombardment’ environment of the Earth environment of the Earth up to 0.75 Gyrup to 0.75 Gyr
• ... ... εε Eri is 0.85 Gyr old Eri is 0.85 Gyr old di Folco et al. 2004; VLTi stellar di Folco et al. 2004; VLTi stellar
radius dataradius data
image courtesy online Encyclopedia of Astrobiology Astronomy & Spaceflight
SCUBA observationsSCUBA observations
started Aug 1997 started Aug 1997 • 850 850 μμmm
• 450 450 μμm (effectively m (effectively from 2000)from 2000)
why SCUBA?why SCUBA?• first submillimetre first submillimetre
cameracamera
• resolution of 8-15”resolution of 8-15”
• to ~mJy-rmsto ~mJy-rms
see Holland et al. 1999
from the start...from the start... by night 1.... by night 1....
• 1 hour frame1 hour frame
“ “another Solar another Solar System !? ”System !? ”
first imagefirst image mystery solved!mystery solved!
• there really there really isis an an inner hole in a disk inner hole in a disk seen ~face-onseen ~face-on
• cavity extends to cavity extends to ~Neptune’s orbit~Neptune’s orbit
• but only half-but only half-cleared, so any exo-cleared, so any exo-Earth likely to be Earth likely to be massively massively bombardedbombarded
Greaves et al. 1998
major outcomesmajor outcomes really a dust diskreally a dust disk size ~ of Solar Systemsize ~ of Solar System
• radius of 65 AUradius of 65 AU
with large cleared cavitywith large cleared cavity• to ~ 30 AUto ~ 30 AU
inclination ~ tilt of stellar poleinclination ~ tilt of stellar pole• i ~ 25i ~ 25°°
‘‘evolved’ dust, i.e. debrisevolved’ dust, i.e. debris• ββ ~ 1.0 ~ 1.0
LUMPS!LUMPS!
need for moreneed for more SCUBA upgrades in late 1999SCUBA upgrades in late 1999
-> better 450 -> better 450 μμm filterm 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
1997-2002 images1997-2002 images at 850 at 850 μμmm
• clumps confirmedclumps confirmed
Greaves et al. 2005
first results at 450first results at 450 at 450 at 450 μμmm
• clumps similar to 850clumps similar to 850 independentindependent data, data,
different detectorsdifferent detectors ~20 hours integration~20 hours integration
• clump to west has clump to west has 350 350 μμm counterpart? m counterpart? (SHARC II)(SHARC II)
planetary resonances?planetary resonances? dust caught in resonances dust caught in resonances
with a planet forms with a planet forms characteristic patternscharacteristic patterns- > pinpoint planet location- > pinpoint planet location
why it’s hard in practice: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
interpretationsinterpretations
Quillen & Thorndike 2002:
0.1 MJup at a = 40 AU, e = 0.3
Ozernoy et al. 2000:
0.2 MJup at a = 60 AU, e = 0
any hard evidence?any hard evidence? the inner planet:the inner planet:
• ~2 M~2 MJupJup, a ~ 3.5 AU, e , a ~ 3.5 AU, e
~ 0.4~ 0.4
SCUBA: disk centre SCUBA: disk centre offset offset from starfrom star• by ~1-2” by ~1-2”
• evidence of evidence of eccentricity forced on eccentricity forced on planetesimals?planetesimals?
an outer planet?an outer planet?
clearing clearing andand clumps seen clumps seen • all by one outer planet?all by one outer planet?
rotation expectations:rotation expectations:
• period ~ 180-570 years!period ~ 180-570 years! from just inside cavity, to from just inside cavity, to
embedded in dust ringembedded in dust ring
• but in a few years, high S/N but in a few years, high S/N clump centre should move by clump centre should move by detectable amount (~arcsec)detectable amount (~arcsec)
what’s really disk?what’s really disk? first submm proper motion experiment!first submm proper motion experiment!
• background objects have background objects have notnot moved 4.5” with star moved 4.5” with star
850 μm: colour, 1997/8 datacontour, 2000/1/2 data
rotation?rotation? tentative!tentative!
• but but systematicsystematic patternpattern
• proper motion plus proper motion plus rotation signature rotation signature seenseen
background blends background blends are a problemare a problem
simulationssimulations method:method:
• simulate a dust ring with clumps, for 15” beam simulate 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-viewsimulate SCUBA chopping on/off field-of-view
• produce ‘old’ and ‘new’ images, with known produce ‘old’ and ‘new’ images, with known proper motion and chosen rotationproper motion and chosen rotation
• χχ22-fitting to recover proper motion & rotation-fitting to recover proper motion & rotation
simplifications: simplifications: circular, star-centred, face-on ring; point-like clumpscircular, star-centred, face-on ring; point-like clumps
detecting rotationdetecting rotation scatter found in simulations is scatter found in simulations is 55° (1° (1σσ))
• when no rotation includedwhen no rotation included errors may differ with rotating clumps errors may differ with rotating clumps
χχ22-fitting gives 11-fitting gives 11° for ° for realreal 4.5-yr dataset 4.5-yr dataset
old/new example: 5° error° error
implicationsimplications
if detected:if detected:• planet at ~27 AU with ~150-yr periodplanet at ~27 AU with ~150-yr period
hence is both clearing and perturbing dust ringhence is both clearing and perturbing dust ring
• furthest-out exo-planet detection!furthest-out exo-planet detection!
still need to model resonances to still need to model resonances to identify:identify:• planet’s present position, mass, and planet’s present position, mass, and
orbital eccentricityorbital eccentricity
how to extend the techniquehow to extend the technique
could be a major planet-finding could be a major planet-finding tool, withtool, with
• higher resolutionhigher resolution e.g. 1-month experiments for ALMA!e.g. 1-month experiments for ALMA!
• more sensitivitymore sensitivity εε Eri is close, and ~median mass of Eri is close, and ~median mass of
detecteddetected debris disks, for Sun-like stars debris disks, for Sun-like stars
unique for distant planets?unique for distant planets?
discovery spacediscovery space SCUBA-2 Legacy SurveySCUBA-2 Legacy Survey
• JCMT, from 2007JCMT, from 2007
• 500 stars, to the 850 500 stars, to the 850 μμm m sub-mJy confusion limitsub-mJy confusion limit
Large Submm TelescopeLarge Submm Telescope• plans for ~30-100 m-classplans for ~30-100 m-class
• to 200 to 200 μμm?m?- > order of mag in resolution- > order of mag in resolution
summarysummary
εε Eri is the nearest young-Solar Eri is the nearest young-Solar System analogue System analogue • history of cometary bombardmenthistory of cometary bombardment
demonstrates detection of outer demonstrates detection of outer planet perturbing cometary beltplanet perturbing cometary belt• new robust method of using rotationnew robust method of using rotation