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Debris Disks, Small Bodies, and Planets

Debris Disks, Small Bodies, and Planets. Alexander V. Krivov Astrophysical Institute and University Observatory Friedrich Schiller Universit y Jena. 4th Planet Formation Workshop Heidelberg, 1-3 March 2006. Components of a “mature” planetary system.

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Debris Disks, Small Bodies, and Planets

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  1. Debris Disks, Small Bodies, and Planets • Alexander V. Krivov • Astrophysical Institute • and University Observatory • Friedrich Schiller University Jena 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  2. Components of a “mature” planetary system Circumstellar material Planetesimals Star Debris disk Planets 1. Debris disks stem from small bodies 2. Debris disks are sculptured by planets – directly and via small bodies 3. Debris disks are easier to observe than planets and small bodies => important! 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  3. Outline • New observations • Debris disks themselves • Debris disks and small bodies • Debris disks, small bodies and planets • Summary 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  4. New Observations

  5. Spitzer / MIPS: huge (1000AU) featureless disk seen pole-on Su et al., ApJ 628, 427 (2005) “The Big Four“ (a Lyr, b Pic, e Eri, a PsA) revisited Vega Holland et al., Nature 392, 788 (1998) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  6. Greaves et al., ApJ 619, L187 (2005) JCMT / SCUBA five years after discovery: signs of rotation, at least three features real “The Big Four“ (a Lyr, b Pic, e Eri, a PsA) revisited Eridani Greaves et al., ApJ 506, L133 (1998) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  7. “The Big Four“ (a Lyr, b Pic, e Eri, a PsA) revisited bPic Wahhaj et al. (2003) Weinberger et al. (2003) Telesco et al. (2005) New images of the inner disk (<100AU) Galland et al., AAp 447, 355 (2006) New radial velocity constraints on presumed planets: no Jupiter inside 1AU 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  8. New disks resolved (vis, IR, sub-mm) AU Mic M1Ve 0.5 Msun 0.1 Lsun ~20 Myr 9.9 pc vis and NIR, 88” U. Hawaii and Keck Kalas et al. Science 303, 1990 (2004) Liu, Science 305, 1442 (2004) Coeval with b Pic, but an M-type star 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  9. New disks resolved (vis, IR, sub-mm) t Cet HD 32297 A0 30 Myr? 110 pc vis and NIR, NICMOS and 88” U. Hawaii G8V, ~10 Gyr, 3.7 pc sub-mm, JCMT / SCUBA Greaves et al., MNRAS 351, L54 (2004) Schneider et al., ApJ 629, L117 (2005) Kalas, ApJ, 633, L169 (2005) Older than the Sun! 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  10. Many more unresolved disks (IR excesses) More than 300 disks in total Meyer et al., ApJS 154, 422 (2004) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  11. Statistics: age dependence Protoplanetary disks Transitional disks Debris disks • Large drop after 10Myr • No change after 400Myr, a linear decay instead • (cf. Habing et al., Nature 401, 456 ,1999) • No obvious dependence on central star's properties Greaves, Science 307, 68 (2005) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  12. Nearly all stars with debris disks have distant planets ...but (almost) no stars with RV planets have debris disks Statistics: stars with disks vs stars with planets Greaves et al., MNRAS 348, 1097 (2004) Saffe & Gomes (2004) and Beichman et al (2005) came to different conclusions. The question remains open... 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  13. Debris Disks Themselves

  14. Birth, life, and death of dust grains 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  15. Dust sources: • planetesimals (collisions) • comets (activity) • grain-grain collisions Dust evolution: • Stellar gravity • Direct radiation pressure • Poynting-Robertson drag • Grain-grain collisions • Gas drag • Gravity of planets • Lorentz force Dust sinks: • sublimation • collisions and RP blowout • ejection by planets Birth, life, and death of dust grains 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  16. Stellar gravity + radiation pressure Talks by Gerhard Wurm & Oliver Krauss Direct radiation pressure only “reduces” the mass of the star, dust grain orbits remain Keplerian 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  17. Stellar gravity + radiation pressure • a-meteoroids (in bound, elliptic orbits) • two types of b-meteoroids (in unbound, hyperbolic orbits) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  18. Stellar gravity + radiation pressure A typical boundary between a- and b-meteoroids: 1-10 mm 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  19. Poynting-Robertson drag Wyatt & Whipple, ApJ 111, 134 (1950) Breiter & Jackson, MNRAS 299, 237 (1998) • Orbits of a-meteoroids shrink and circularize • The grains eventually sublimate near the star 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  20. Collisions Rates Outcomes Collisional time ~ orbital period 10 optical depth ~ 10-1000 orbital periods => collisions are frequent Min relative velocity for fragmentation: ~100m/s Random velocities in a disk: ~1km/s => collisions are disruptive Largest fragment's mass / collider's mass (assuming 1km/s relative velocity): ~10-3 => pounding is efficient Collisional grinding: pebbles ... sand ... fine dust... 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  21. Poynting-Robertson drag vs collisions bPictoris Zodiacal cloud Leinert & Grün, In Phys.of Inner Heliosphere (1990) Krivov, Mann & Krivova, AAp 362, 1127 (2000) Except in old dilute disks, P-R drag plays a minor role! 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  22. Dynamical arguments: very little gas (gas:dust < 1:1)Thebault & Augereau, AAp 437, 141 (2005) Gas drag Talk by Inga Kamp Contradictory observations ofbPic and AU Mic (12Myr): much gas (gas:dust ~ 100:1)Thi et al. (2001), Brandeker et al. (2004),... little gas (gas:dust < 6:1)Lecavelier et al. (2001), Roberge et al. (2005),... Consequences: gas planets must already have formed there, and there is evidence for that (e.g., Mouillet et al. 1997, Liu 2004) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  23. Size distribution (the Vega disk example) Poster by Torsten Löhne Dohnanyi's (1969) power law (alpha-meteoroids only) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  24. Size distribution (the Vega disk example) Poster by Torsten Löhne beta-meteoroids Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  25. Size distribution (the Vega disk example) Poster by Torsten Löhne Krivov, Löhne & Sremcevic, AAp (submitted) ...timescales depend on distance... 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  26. Size distribution (the Vega disk example) Poster by Torsten Löhne Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  27. Size distribution (the Vega disk example) The steady state distribution Krivov, Löhne & Sremcevic, AAp (submitted) Dominant size, waviness, presence of b-meteoroids 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  28. Radial distribution (the Vega disk example) The steady state distribution Krivov, Löhne & Sremcevic, AAp (submitted) There is an upper limit on the radial slope 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  29. Debris Disksand Small Bodies

  30. Short-term evolution of debris disk Non-steady-state: e.g. due to recent major collisions (Wyatt & Dent, MNRAS 334, 589, 2002; Kenyon & Bromley, AJ 130, 269, 2005) Supercollision Dust clump Longitudinal spread and formation of a dust ring Radial spread outward in ~0.1-1 Myr Krivov, Löhne & Sremcevic, AAp (submitted) Poster by Torsten Löhne 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  31. Long-term evolution of debris disk Collisional depletion of parent bodies(Dominik & Decin, ApJ 598, 626, 2003) EKB Krivov, Sremcevic & Spahn, Icarus 174, 105, (2005) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  32. Long-term evolution of debris disk Collisional depletion of parent bodies(Dominik & Decin, ApJ 598, 626, 2003) Vega disk EKB Krivov, Sremcevic & Spahn, Icarus (2005) Krivov, Löhne & Sremcevic, AAp (submitted) A nearly 1/ t decay of parent body populations should cause gradual depletion of debris disks over Gyr-scales 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  33. Debris Disks, Small Bodies,and Planets

  34. Global structure – asymmetries and warps Observed in several resolved disks 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  35. Global structure – asymmetries and warps Suggested explanation: secular perturbations from an embedded planet Offset (e, ) Warp (i, ) warp is spreading outwards (Mouillet et al., AAp (1997): Rwarp =Rwarp (Mstar , Mplanet , aplanet , time) (alternatively, asymmetry can stem from the disk-ISM interaction) Artymowicz & Clampin, ApJ (1997) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  36. Radial substructure - inner gaps Talk by Sebastian Wolf Seen in resolved disks Inferred from SEDs Curves: w/o planets, grey bands: with planets Greaves et al., ApJ 506, L133 (1998) Moro-Martin, Wolf & Malhotra, ApJ 621, 1079 (2005) Inner gaps with radii of a few to a few tens of AU are found to be typical 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  37. Radial substructure - inner gaps Scenario I: • Dust production in a planetesimal belt • P-R drift of dust inward to planet orbit • Planet acts as a dynamical barrier Scenario II (simpler, robuster!) • Dust production in a planetesimal belt • Subsequent collisional cascade • RP spreads dust outward from the belt Both scenarios look plausible, both require a planet to confine the planetesimal belt 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  38. Radial substructure - rings Observed in several resolved disks Images: evidence for several rings of large dust Spatially-resolved spectrophotometry: evidence for several rings of fine dust Wahhaj et al. (2003) Weinberger et al. (2003) Telesco et al. (2005) Okamoto et al., Nature 431, 660 (2004) Poster by Florian Freistetter 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  39. A simple kinetic model: localized dust production, P-R drag and collisions Wyatt, AAp 433, 1007 (2005) Dermott et al, Nature 369, 719 (1994) Radial substructure - rings Scenario I: • Dust production “somewhere” outside • P-R drift of dust inward to resonances • Ring formation almost at planet orbit Scenario II (simpler, robuster!) • Dust production in a planetesimal belt • Therefore, higher dust density there • Ring appears at the belt location Both scenarios look plausible 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  40. Azimuthal substructure - clumps Eridani Poster by Martina Queck Observations Models Liou et al. (2000): ~1MJ, ap=40AU, ep=0.01 Ozernoy et al. (2000): 0.2MJ, ap=55-65AU, ep=0 Quillen & Thorndike (2002): 0.1MJ, ap=42AU, ep=0.3 Deller & Maddison (2005): the same + 2nd planet @ 10-18 AU Greaves et al., ApJ 506, L133 (1998) Quillen & Thorndike, ApJ 578, L149 (2002) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  41. Azimuthal substructure - clumps Edgeworth-Kuiper belt Observations Models ...none ... Liou & Zook, AJ 118, 580 (1999) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  42. Clumps Voids Inner gap Azimuthal substructure - clumps Standard scenario: P-R drift & trapping in exterior MMRs Planet Star Theory (trapping efficiency, timescales etc) (Beauge, Ferraz-Mello, Jackson, Lazzaro, Liou, Roques, Scholl, Sicardy, Weidenschilling, ... (1990s) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  43. Azimuthal substructure - clumps Difficulties with this scenario P-R timescale and timescale of resonant eccentricity pumping >> timescale of collisional destruction ! 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  44. Alternative scenario: • Dust production in a family of resonant planetesimals • Dust remains in the same resonance Wyatt, ApJ 598, 1321 (2003) Works always (but requires~0.1-1 Mearth in planetesimals) Azimuthal substructure - clumps Standard scenario: • Dust production in a planetesimal belt • P-R drift of dust inward to resonances • Capture and formation of clumps Works only in disks with t > 10-5! Krivov, Queck & Sremcevic, in prep. Poster by Martina Queck 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  45. Summary

  46. Debris disks are: • a natural component of planetary systems at later evolutionary stages, and therefore important objects to study; • maintained by, and deliver information on, small body populations; • indicators of planets; 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  47. Studies of debris disks complete the census of planetary systems and can certainly contribute to answering the great question: “How do the planetary systems form and evolve?” 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

  48. Many thanks to my collaborators Torsten Löhne (poster!) Martina Queck (poster!) Florian Freistetter (poster!)

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