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Observations, Modeling and Theory of Debris Discs

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Observations, Modeling and Theory of Debris Discs Observations, Modeling and Theory of Debris Discs Brenda Matthews (HIA, Canada) Geoff Bryden (JPL) Carlos Eiroa (Universidad Autonoma de Madrid) Alexander Krivov (University of Jena) Mark Wyatt (Institute of Astronomy) Physical picture • Debris disks are produced from the remnants of the planet formation process • They are evidence that systems were able to produce at least planetesimal-scale oligarchs (100s of km) • Second generation dust is produced through collisional processes • Debris discs include – Planetesimals (unseen), potentially in narrow “birth rings” – Dust produced from collisions (detected optical centimetre) – All size scales in between 05/28/13 Protostars & Planets VI Courtesy: Zoe Leinhardt Onset of Debris phase 10 Myr Protoplanetary Debris Hernandez et al. 2008, 686, 1195 Dust from 0.1 – 100 AU Dust in belts Massive gas disk No gas Panić et al. 2013, MNRAS, accepted Accretion onto star No accretion (after Wyatt 2008 ARA&A, 46, 339) Optically thick Optically thin 05/28/13 Protostars & Planets VI Detecting Debris Discs Scattered light Thermal emission Shows up subtle structures Highlights larger grains Highlights position of small Can reveal hot/warm/cold grains components Extent of outer disc/halos Can trace the “birth ring” of Does not trace planetesimal planetesimals “birth ring” Resolution has been a Inner region blocked See poster limitation in the past 2B072 (Debes) 05/28/13 Protostars & Planets VI Why we think debris systems could have planets Dust replenished by km- sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric rings Some disks are asymmetric Some systems actually have planets Kalas et al. (2008) Nature / ISAS / JAXA 05/28/13 Protostars & Planets VI Why we think debris systems could have planets Dust replenished by km- Kalas et al. 2008, Science, 322, 1345 sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric, offset rings Some disks are asymmetric Some systems actually have planets Marshall et al. 2011, 05/28/13 Protostars & Planets VI A&A, 529, 117 Why we think debris systems could have planets Dust replenished by km- HD 202628 sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric rings Krist et al. 2002 Some disks are asymmetric Greaves et al. 2013, Some systems actually have in preparation planets 05/28/13 Protostars & Planets VI Why we think debris systems could have planets Dust replenished by km- sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric rings Some disks are asymmetric Some systems actually have planets Kalas et al. (2008) Heap et al. 2000, ApJ, 539, 435; Golimowski et al. 2006, AJ, 131, 3109; 05/28/13 Protostars & Planets VI Lagrange et al. 2010, Science, 329, 57 3 ways planets interact with discs The orbits of disk particles can be affected by a planet’s gravity in 3 ways: 1. Secular perturbations 2. Resonances 3. Scattering eccentric planet See poster 2B075 (Dawson) inclined planet Movies from Mark Wyatt The challenge: " Debris discs are faint 10-4 Blue: A stars (Su06) Red: FGK stars (E13) Green: FGK stars (T08) 10-5 Purple: AFGKM (M13) 10-6 M K G F A 10-7 Su et al. 2006, ApJ, 653, 675; Eiroa et al. 2013, A&A, in press; Trilling et al. 2008, ApJ, 674, 1086; Matthews et al. 2013, in preparation 05/28/13 Protostars & Planets VI Incidence rates Note that surveys each have their own excess limit that is detectable. It is possible that all stars have discs at some level with many below the detection thresholds. A stars FGK stars M stars 25-35% 3 - 20% Very few! 2.2, 24, 70, 100 um 24, 70, 100/160 um 24, 70, 100, 850 um Chen et al. 2012, ApJ, 756, 133 Carpenter et al. 2009 Gautier et al. 2007 Chen et al. 2011, ApJ, 738, 122 Hillenbrand et al. 2008 Liu et al. 2004 Su et al. 2006, ApJ, 653, 675 Trilling et al. 2008 Lestrade et al. 2006 Absil et al. 2013, Eiroa et al. 2013 Lestrade et al. 2013 Thureau et al. 2013, in prep Sibthorpe et al. 2013, in prep Matthews et al. 2013, in prep Comparable to rate of planets Excellent agreement at all Increasing incidence with wavelengths. aroundwavelength. FGK stars (16%) from Except for very young M stars, Decreases with age. KeplerDecreases with periods with age up toto ~ 85 1Gyr. generally these discs remain days (Fressin et al. 2013) elusive. 05/28/13 Protostars & Planets VI Dust excess evolution • Spitzer studies of the 24 and 70 excesses (Ftot/F*) of A stars found a ∝ t-1 decline in the upper envelope on decay timescale of 150 Myr at 24 µm but longer (~400 Myr) at 70 µm 05/28/13 Protostars & PlanetsRieke VI et al. 2005, Su et al. 2006 Spitzer A star evolution See poster 2B070 (Vican) KB • Luminosity decline relative to the star is evident • 24 micron excess declines fastest (~0 by 400 Myr), suggesting an inside out evolution of the dust (warmer dust is lost first) 05/28/13 Protostars & Planets VI Su et al. 2006 Long term evolution • Steady-state cascade implies that, at any age, disc cannot be dustier than a certain limit • Most discs are consistent with this and are “KBs” • systems with hot dust are not consistent Wyatt et al. 2007; Loehne et al. 2008 with this picture See poster 2B071 (Bonsor) 05/28/13 Protostars & Planets VI Zones of dust distance increases edge-on view of a planetary system temperature decreases planetesimal belt terrestrial planets giant disk halo planets ∼1500 K ∼300 K terrestrial zone ∼150 K ∼50 K See poster 2B074 asteroidal Kuiper-belt (van Lieshout) zone zone wavelength increases 2 µm ∼10 µm ∼24 µm ∼60-70 µm very hot hot warm cold 05/28/13 Protostars & Planets VI Wavelength and Resolution Spitzer SCUBA: Holland et al. 1998, Nature, 392, 788 Spitzer: Stapelfeldt et al. 2004, ApJS, 154, 458 HST: Kalas et al. 2005, Nature, 435, 1067 Herschel: Acke et al. 2012, A&A, 540, 125 ALMA: Boley et al. 2012, ApJ, 750, 21 SCUBA 05/28/13 Protostars & Planets VI Resolved Kuiper Belts • DUNES and DEBRIS both find ~50% detected discs are resolved • wealth of information from resolved images & SEDs • fit Tdust, rdisc, spectral slope • Inclination, position angle • find Ldust/Lstar, Mdisc, rdisc/rblackbody • Dust grain sizes/compositions See posters 2B073 F-star Gamma Dor (Pawellek) (Broekhoven-Fiene et al. 2013) 05/28/132B069 (Schüpper) Protostars & Planets VI Alignment of discs and stars 12 systems have disc and stellar inclinations independently measured (incl. Sun) 1&2$ 34567!! 385--"6!7 2$99$58:* ;<= 385--,0-7 385/">!, 385-00 #$%&'%()& &$*#('%()& Alignment within 10 &)?5@*A 385-7!., 385-/-,-- BC5DAE 9A=<?5-"F5:GG?&% )#<?5-"F5:GG?&% degrees for all systems .+" 2' 0%1 %3'4'' consistent 2' #50 %6' Suggests larger separation -+, planetary inclinations likely to be aligned as -+" well, unlike close-in " /" 0" !" %1#7%1+$%51'5"'' 6%0#'-6!8*!!0/' planets (Brown et al. !""" "+, 2012; Simpson!""!#$%&!'$!()!*+$,*!'-./ et al. ' 2011; Triaud et al. 2010; Winn et al. 2010) "+" Greaves, Eiroa, Matthews et al. in preparation 05/28/13 Protostars & Planets VI Radial distance (AU) 39.4 394. 70µm ) 2 100 10-1 -2 Halos: HR 879910 Data Median Data Surface brightness (mJy/arcsec Model convolved RawRadial Model distance (AU) 1039.4-3 394. 10070µm ) ) 2 • Cold, very extended extensions2 of debris discs, dominated by blow-out1000 grains on hyperbolic or bound orbits10-1 -1 • Planetesimal belt: 100 – 310-2 AU -2 10 Data Median Data Surface brightness (mJy/arcsec Surface brightness (mJy/arcsec Model convolved • Halo: 310 – 2000 AU Raw Model 10-3-3 100160µm 1 10 ) ) 2 2 100 100 100 10-1 (Jy) -1 i -1 10 F 10 10-2 Surface brightness (mJy/arcsec Surface brightness (mJy/arcsec -2 10 -3-2 10 1 10 160µm Radial distance (") ) 153 K 36 K 2 10-3 -1 0 1 2 3 10 10 10 10 10 100 wavelength (!m) λ0 ~ 47 +/- 30 µm β ~ 1.0 +/- 0.1 10-1 05/28/13 Protostars & Planets VI Matthews et al. 2013, in prep Surface brightness (mJy/arcsec 10-2 1 10 Radial distance (") HD 207129 G2V star with no evidence of a halo and no detected planets Evidence of transport of material inward in the disc Disc appears larger with increasing wavelength Marshall et al. A&A 529,A117 (observational) Löhne et al. A&A 537, A110 (detailed modelling) 05/28/13 Protostars & Planets VI Cold disc candidates • Six "cold disk" candidates. These disks have temperatures close to blackbody. • They may be belts of unstirred primordial macroscopic grains that failed to grow to planetesimal sizes. Krivov et al. 2013, ApJ, 772, 32 Eiroa et al. 2011 05/28/13 Protostars & Planets VI Standard model for a debris disc • Radiation pressure blowout • Canonical model of narrow limit “birth ring” • Power law with slope 3-4 • Highly stirred discs produce • Peaks at larger sizes in the case halos of lower stirring (blue curve) • Halos are depressed quickly • Similar effect if there is strong with decreased stirring grain transport (top to bottom) • Strong transport means no halo Krivov05/28/13 et al. 2006; Thebault & AugereauProtostars 2007; & WyattPlanets VI et al. 2011, review chapter & others See posters 2B065 (Ertel) Asteroid belt analogues 2B068 (Kennedy) • Warm dust – Exozodiacal analogs – 1- several AU (habitable zone) ALMA HST 0.6 – mid-IR, Spitzer, IRAS, WISE 870 µm µm • ~1% of stars (or less) in any census • incidence is much lower than for cold dust • component now detectable with ALMA as well Boley et al. 2012; Macgregor et al. 2012 05/28/13 Protostars & Planets VI Warm dust statistics 100 Observed distribution Combined model WISE data can detect -1 m 10 bright exo-Zodis where µ KIN the disk-to-star flux ratio at 12 is better than 0.1 star 10-2 /F disk LBTI will reach 10-3 considerably fainter limits Fraction > F 10-4 Important for target ~Solar System level ~TPF limit LBTI limit WISE limit selection for TPF 10 -4 10 -3 10 -2 10 -1 10 0 10 1 Fdisk/Fstar at 12µm Kennedy & Wyatt 2013 05/28/13 Protostars & Planets VI Vega and Fomalhaut MSX MSX MIPS IRTF IRS PACS PACS IRS ALMA SMA Su et al.
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