1 / 16

Current efforts for modeling exozodiacal disks

Current efforts for modeling exozodiacal disks. Jean-Charles Augereau & Olivier Absil LAOG, Grenoble, France & U. Liège , Belgium Barcelona, September 2009. Various kind of models. Radiative transfer

sirius
Télécharger la présentation

Current efforts for modeling exozodiacal disks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Current efforts for modeling exozodiacal disks Jean-Charles Augereau & Olivier AbsilLAOG, Grenoble, France &U. Liège, BelgiumBarcelona, September 2009

  2. Various kind of models • Radiative transfer • To reproduce the scarce exozodi measurements, in particular IR interferometric data (CHARA/FLUOR, KIN) • To reproduce extreme Spitzer spectra showing unusually large amount of warm dust and clear spectral features (e.g. Lisse et al. 2009) • Dynamical modeling • Sculpting of an asteroid/dust belt by a planet: capture in mean motion resonances (e.g. Stark et al. 2008) • Larger scale models, with outward planet migration toward a Kuiperbelt • Sudden event, e.g. Nice LHB model (Booth et al. 2009) • More progressive (Vandeportalet al., in prep.) • Collisional models to evaluate lifetime of asteroid belts due to collisions (works by Krivov, Löhne, Thébault)

  3. ISSI working group on exozodis • ISSI international team assembled in order to • Interpret the pioneering observations of exozodis with (near-)IR interferometers • Identify the dominant source of dust (dust transport, collisions, comet evaporation) • Predict the structure and amount of dust that can be expected around nearby stars • Help to prepare future missions aiming at finding planets in the habitable zone • Two one-week meetingswere held (August 2007,April 2009) • Next and last meetingin 2010Anyone interestedto attend should contactJean-Charles Augereauaugereau@obs.ujf-grenoble.fr ISSI team: Exozodiacal dustdiks and Darwin

  4. Exozodis: are they zodi analogs? • Fit of the 2.2μm excess with the Solar system zodiacal model : • Vega : 3000 zodisto reproduce the CHARA K-band excess • Fomalhaut : 5000 zodis to reproduce the VLTI/VINCI K-band excess • Problem: it predicts too much flux in the mid-IR (by ~ an order of magnitude) • Our zodi is not representative : detected exozodis have dust much closer to the star ZODIPIC package [Kuchner] Flux 2.2 μm 10 μm Exozodiemissionspectrum Wavelength

  5. Exozodis : radiative transfer • Development of an optically thin exozodiacaldisk model, based on debris disk model by Augereau et al. (1999) • Scattered light and thermal emission • Parametric surface density profiles and size distribution • Variable dust composition (silicates, carbonaceous grains, porosity, …) • Specific treatment of the exozodidisk inner edge to account for thesize-dependent sublimation radius • Outcome of the model: • Peak position of surface density • Grain properties (size, composition) • Mass, optical thickness • Typical dynamical time-scales (vs collisions, radiation pressure) - Solid line : 50% silicates + 50% carbons- Dashed line: 100% carbons

  6. Exozodis : radiative transfer • Result for Vega(Absil et al. 2006) • All parameters go in the same direction: shifting the exozodi spectrum to shorter wavelengths compared to our zodi • Smallgrains (mostly < 1 µm) at distances ~ 0.2 – 0.5 AU • Highly refractive grains, no silicate feature  carbons > 50% • Steepdensity profile: S(r) ~ r-4 (or steeper) Total Thermal emission only MMT/BLINCupperlimit

  7. Exozodis : radiative transfer • Tau Ceti (Di Folco et al. 2007)Solar-type star (G8V at 3.65pc) Spitzerupperlimits

  8. Exozodis : radiative transfer • Zeta Aql(Absil et al. 2008): • More and more similar cases foundwith CHARA/FLUOR • ~20% of stars? • Depends on spectral type 0.6-0.65 Msun 5.5-8AU

  9. Other types of detections • Spitzer/IRS (see Chas’ talk) • Mid-IR imaging on 10-m telescopes • VISIR, T-ReCS, Michelle, etc • Only in favourable cases (~5 so far)due to limitedresolution/sensitivity • JWST/MIRI will do muchbetter • Mid-IR interferometry (see Chas’ talk) • BLINC, KIN, (MIDI) • All detections are showing large amounts of warm/hot dust HD 32297 (Moerchen et al. 2007)

  10. Vega’s exozodi : origin of the dust? • Exozodiacal dust grains have very short lifetimehigh dust production rate,~10-8Mearth/yr for Vega • Equivalent to 1 medium-sizedasteroid every year • Equivalent to a dozen ofHale-Bopp-like cometspassing every day(400 tons of dust per second) • Equivalent to 10-3 the mass ofthe Vega Kuiper Belt per Myr • If we exclude the case ofa dramatic event, the questionis: where does all thisdust come from?

  11. Vega’s exozodi : origin of the dust? • Inward migration of grains due to Poynting-Robertson drag is excluded : too slow compared to other dynamical timescales (collisions, radiation pressure) • Steady-state evolution of an asteroid belt excluded: km-sized bodies in a 10-3MEarth belt at around 0.2-0.5 AU do survive ~105years (Löhne& Krivov, priv. communication – see also Wyatt et al. 2007) • Reservoir of mass inVega’s Kuiper Belt(~85AU, ~ 10MEarth). • How to extract 10-3 of this mass every Myr and transportit well inside 1AU? Planets can help… Schematic representation of the Vega system

  12. Vega: planet migration • Structures in Vega’s Kuiper belt : migrating planet trapping the parent bodies of the dust grains in MMR • Wyatt (2003): Neptune-mass planet,migrating from 40 AU to 65 AU,at a rate of 0.5 AU/Myr. Circular orbits. • Reche et al. (2008): Saturn mass planet, with e<0.05,and relatively cold disk (<e> < 0.1) 2:1 MMR 3:2 MMR

  13. Vega: the comet factory • A two planet system … • Migrating Saturn mass planet [Wyatt 2003, Reche et al. (2008)] • 0.5 – 2 Jupiter mass planet inside • … and a Kuiper Belt … • … to produce star-grazing comets.Numerical simulations with SWIFT (symplectic integrator).Counting of the test particles entering the 1AU zone

  14. Vega: the comet factory • A two planet system: • Migrating Saturn mass planet [Wyatt 2003, Reche et al. (2008)] • A 0.5 Jupiter mass planet at ~20 – 25 AU does the job well: Sufficient rate of cometsin the 1AU zone for 40Myr Resonant structuresat 85AU preserved

  15. More extrasolar LHBs? • See M. Booth’s poster • Constrain: MIPS statistics • ~12% of debrisdisksystemsaffected by LHB event? • Mid-IR excessshort-lived • Expect (very) few detections

  16. How does all this help? ~100 zodi • Asymmetries • Most problematicexozodifeature (but alsointeresting on theirown) • Couldtheybepredicted? • Dust sources need to beknown • Planetary system architecture matters • Extrapolate the Bryden exo-Kuiper belthistogram? • Alsovalid for exozodis? • How deepshouldwesurvey to make sure that XX % of exozodis are < 10 zodi? • Can werely on statisticsonly? • Do weneed to observe the exozodis of actual candidate targets? ( wait for SIM’s input)

More Related