1 / 50

Observations of Disks around Young Stellar Objects

Observations of Disks around Young Stellar Objects. G. Duch êne & F. Ménard (Obs. Grenoble). Goals of this talk. Consider as wide a range of datasets as possible in 30 minutes! Will skip some very exciting aspects Discussion of selected physical aspects Leave out gas and chemistry

lindsey
Download Presentation

Observations of Disks around Young Stellar Objects

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. Observations of Disks around Young Stellar Objects G. Duchêne & F. Ménard (Obs. Grenoble)

  2. Goals of this talk • Consider as wide a range of datasets as possible in 30 minutes! • Will skip some very exciting aspects • Discussion of selected physical aspects • Leave out gas and chemistry • Persuade you that we can now constrain some physical processes • Yet many open questions remain… G. Duchêne - Structure Formation in the Universe - May 2007

  3. Outline • General motivation • Observational methods • Disks in the context of star formation • Disks in the context of planet formation • Debris disks: after planets formed • Summary and perspectives G. Duchêne - Structure Formation in the Universe - May 2007

  4. General Motivation G. Duchêne - Structure Formation in the Universe - May 2007

  5. Why do we care about disks? A natural outcome of star formation G. Duchêne - Structure Formation in the Universe - May 2007

  6. Why do we care about disks? Planetary system factories A natural outcome of star formation G. Duchêne - Structure Formation in the Universe - May 2007

  7. Expected physical processes (I) • Influence of central star/environment • Disk lifetime • Total mass reservoir • Overall structure • Disk dispersal mechanism • Viscous dissipation of angular momentum • Photo-ionization • Dynamical dispersal (companion) G. Duchêne - Structure Formation in the Universe - May 2007

  8. Expected physical processes (II) • Substructure formation • Spiral arms (instabilities, planets) • Gap openings (planets) • Dust evolution • Grain growth • Radial migration • Vertical sedimentation • Change in grain structure G. Duchêne - Structure Formation in the Universe - May 2007

  9. Observations of disks G. Duchêne - Structure Formation in the Universe - May 2007

  10. Unresolved datasets: SEDs • The simplest approach: gather the energy and try to invert to disk structure • Flared disks in most cases Flat Flared Dullemond et al. (2007) Chiang & Goldreich (1997) G. Duchêne - Structure Formation in the Universe - May 2007

  11. Unresolved datasets: SEDs • Useful approach for statistical purposes • Can be dangerous on an object-to-object basis • Need for resolved datasets! Burrows et al. (1996) All Taurus CTTS D’Alessio et al. (2001) G. Duchêne - Structure Formation in the Universe - May 2007

  12. Resolved datasets • A single image provides key parameters: • Outer radius, position angle • Inclination (sometimes) • Optical depth (sometimes) Not a normal disk Guilloteau et al. (1999) Bertout et al. (1998) G. Duchêne - Structure Formation in the Universe - May 2007

  13. Resolved datasets grain size VLT/VISIR composition structure Interf. Spitzer mass All probe different dust populations G. Duchêne - Structure Formation in the Universe - May 2007

  14. Resolved datasets VLT/VISIR Interf. Spitzer Need for complementary complex RT models G. Duchêne - Structure Formation in the Universe - May 2007

  15. Disks and Star Formation G. Duchêne - Structure Formation in the Universe - May 2007

  16. Disks and central object mass • How universal is star formation? • Probe disk presence through IR excess • Overall fraction up to 90% (in  Oph) • Best studied population: the ONC • disks at all masses (0.1 - 5 M) Slight deficit at low mass end? Hillenbrand et al. (1998) G. Duchêne - Structure Formation in the Universe - May 2007

  17. Disks and central object mass • Detection is harder around VLMS/BD because of cooler Teff • BDs: 40-75% up to ~5 Myr at least • No substantial difference with stars Jayawardhana et al. (2003) Liu et al. (2003) G. Duchêne - Structure Formation in the Universe - May 2007

  18. Disks and central object mass • Not only is disk frequency independent of mass, their structure is, too! • Hydrostatic (flared) passive disks ~0.1 M ~0.5 M ~2 M IRAS 04158+2805 HK Tau PDS 144 Perrin et al. (2007) Glauser et al. (2007) McCabe et al. (2007) G. Duchêne - Structure Formation in the Universe - May 2007

  19. Disks and central object mass • The special case of high-mass stars: • Aligned (rotating) methanol masers, but not so clear Norris et al. (1993), De Buizer et al. (2003) • Wide-angle outflows • A huge ‘silhouette disk’ • Difficult to conclude yet • Too far away • Evolving too fast 20000 AU M17 Chini et al. (2004) G. Duchêne - Structure Formation in the Universe - May 2007

  20. Disks and orientation of stars • Taurus molecular cloud = series of filaments orthogonal to B field • So are individual pre-stellar cores CO map Prestellar cores Hartmann (2002) G. Duchêne - Structure Formation in the Universe - May 2007

  21. Disks and orientation of stars • Disks around T Tauri stars indicate the system’s symmetry axis • Systems are randomly oriented w.r.t. local magnetic field • What happened? • Non-magnetic collapse? Ménard & Duchêne (2004) G. Duchêne - Structure Formation in the Universe - May 2007

  22. Disks and Planet Formation(overall disk properties) G. Duchêne - Structure Formation in the Universe - May 2007

  23. Disks sizes and masses • Typical disk size ~ 200 AU • Compares well with Solar System • Large scatter around median value! IRAS 04158+2805 HV Tau ~ 1100 AU ~ 40 AU Stapelfeldt et al. (2003) Glauser et al. (2007) Kitamura et al. (2002) G. Duchêne - Structure Formation in the Universe - May 2007

  24. Disks sizes and masses • Disk masses can be derived from thermal radio fluxes/maps • Uncertain dust opacities • Uncertain gas/dust ratio • Derived total masses: • Consistent with MMSN • Consistent with stability Natta et al. (2000) G. Duchêne - Structure Formation in the Universe - May 2007

  25. Disks sizes and masses • Radio interferometers (IRAM, OVRO) can resolve disks • Typical surface density ~1 g.cm-3 @ 100AU • Power law indices • Temperature law • Surface density • ‘Flat’ MMSN-like disks • Good for planets! • But interpolation… Dutrey et al. (1996) G. Duchêne - Structure Formation in the Universe - May 2007

  26. Disk asymmetries: large scales • Evidence for dynamical perturbation: • Companion, planet, high-mass disk? • What you see is NOT what you have… HD 100546 AB Aur Optically thin! Grady et al. (2001) Fukagawa et al. (2004) Piétu et al. (2005) G. Duchêne - Structure Formation in the Universe - May 2007

  27. Disk asymmetries: gaps • Planets embedded in disks open ‘gaps’ • Can these be observed? • Gap size < 1AU • High resolution + high contrast • ALMA? New generation AO? • Remember, however: • Spatial resolution remains an issue • Gaps may be partly filled in G. Duchêne - Structure Formation in the Universe - May 2007

  28. Disk dissipation • Using disk counts in independent SFRs provides survival time of inner disk • Essentially nothing left after 10 Myr • No environment effect • OB vs T associations, clusters • Large bodies may still be present and hidden Disk lifetime Meyer et al. (2000) G. Duchêne - Structure Formation in the Universe - May 2007

  29. Disk dissipation • Does disk dissipation depend on central object mass? • Spitzer surveys of UpSco (~5Myr) • G-B: 5 +/- 2 % • K0-M5: 19 +/- 3% • BDs: 37 +/- 9 % • Disk lifetime is longer for lower mass objects • Because of slower viscous timescale? } Carpenter et al. (2005) Scholtz et al. (2007) G. Duchêne - Structure Formation in the Universe - May 2007

  30. Inner disk dispersal • Disks disappear after inner hole clearing • Evidence shows that disks dissipate inside-out in <105 yrs (viscous timescale) 0.2-0.5 AU material Very few transition objects CoKu Tau 4 D’Alessio et al. (2005) McCabe et al. (2006) 0.5-2 AU material G. Duchêne - Structure Formation in the Universe - May 2007

  31. Inner disk dispersal • How long does the outer disk remain? • Spitzer searches for disk with only outer disk material (>5-10 AU) • Only a few percent of such objects • Outer disk falls below detection threshold in <~ 105 yrs • Too fast for viscosity? Padgett et al. (2006) G. Duchêne - Structure Formation in the Universe - May 2007

  32. Disks and Planet Formation(dust properties) G. Duchêne - Structure Formation in the Universe - May 2007

  33. Grain growth: mm view • First approach: SED slope (mm regime) • Typically, amax ~ few mm to few cm Large grains Observed distribution of spectral indices Small grains D’Alessio et al. (2001) Natta et al. (2007) G. Duchêne - Structure Formation in the Universe - May 2007

  34. Grain growth: silicates view • Silicate feature is size-dependent • Small (< 0.1 m) vs large grains (~1 m) • Larger grains do not contribute • Crystallinity produces sharp features Kessler-Silacci et al. (2006) G. Duchêne - Structure Formation in the Universe - May 2007

  35. Grain growth: silicates view • Clear evolutionary sequence • Larger grains come together with higher grain crystallinity (above a threshold) Higher crystallinity Smaller grains Kessler-Silacci et al. (2006) Van Boekel et al. (2005) G. Duchêne - Structure Formation in the Universe - May 2007

  36. Grain growth: scattered light • Stellar photons can scatter off dust grains at the disk surface • Phenomenon depends on /a • Larger grains scatter preferentially forward, with a lower polarization rate • Images and polarization maps can be used to infer grain sizes • Up to amax ~ few m typically • Advantage: longer  probes deeper!! G. Duchêne - Structure Formation in the Universe - May 2007

  37. Grain growth: scattered light • Single power law size distribution • Increasingly more isotropic scattering • HK Tau images (increasingly ‘peakier’) reveal larger grains inside (up to 3-5 m) VLT/AO Keck/AO Keck/AO Keck 2.2 m 3.8 m 4.7 m 11.3 m McCabe et al. (in prep) McCabe et al. (2003) G. Duchêne - Structure Formation in the Universe - May 2007

  38. Grain growth: the big picture • Each aspect probes • A different region of disks • Different grain sizes/populations • In each case, analysis requires knowledge of additional information (radius, inclination, …) • Ideally, comparison all datasets to a single (complex) radiative transfer model G. Duchêne - Structure Formation in the Universe - May 2007

  39. Vertical sedimentation • If large grains disappear from the surface, thermal equilibrium is changed • Change in disk SED • Difficult to ascertain, however Sedimentation mimics a flat disk Dullemond & Dominik et al. (2004) G. Duchêne - Structure Formation in the Universe - May 2007

  40. Vertical sedimentation • Confront mm regime and silicates • Can be convincing (if composition is well distributed throughout the disk) IM Lup Small and large grains Small grains only Pinte et al. (in prep) G. Duchêne - Structure Formation in the Universe - May 2007

  41. Vertical sedimentation • Confront mm regime and silicates • Can be convincing (if composition is well distributed throughout the disk) IM Lup Small and large grains Small and large grains Small grains only sedimentation Pinte et al. (in prep) G. Duchêne - Structure Formation in the Universe - May 2007

  42. Radial migration • Interferometry + spectroscopy (MIDI) • Silicate features a few AU from the star • Higher crystallinity! • Grain processing? RY Tau (K1) small van Boekel et al. (2004) crystalline Shegerer et al. (subm.) G. Duchêne - Structure Formation in the Universe - May 2007

  43. Radial migration • Difficult to quantify differentiation • Many assumptions in analysis • Nonetheless, there is evidence that grain properties depend on radial distance to the star • However, we cannot prove that grains have migrated! • Crystallinization may be a local processing G. Duchêne - Structure Formation in the Universe - May 2007

  44. Further in time: debris disks G. Duchêne - Structure Formation in the Universe - May 2007

  45. Debris disks: basics • Debris disks are the final stage in planet formation before zodiacal disks • Formed through collisions of solid bodies • They are optically thin • Easier to interpret • Harder to observe • SED is usually limited • Rough constraints only Beichman et al. (2006) G. Duchêne - Structure Formation in the Universe - May 2007

  46. Debris disks: porosity, aggregates • With many independent observables, finer models can be tested • The AU Mic debris disk is made of (small) porous grains porous compact Fitzgerald et al. (2007) G. Duchêne - Structure Formation in the Universe - May 2007

  47. Debris disks: porosity, aggregates • Another debris disk: HD 181327 • All observables cannot be explained simultaneously with spherical grains • Aggregates? SED vs Phase function ? Schneider et al. (2006) G. Duchêne - Structure Formation in the Universe - May 2007

  48. Summary and Perspectives G. Duchêne - Structure Formation in the Universe - May 2007

  49. Summary • We have access to many types of complementary observations • Several physical processes can be (somewhat) constrained • Core collapse/fragmentation • Disk dissipation and inner hole clearing • Grain growth • Dust settling • Presence of planetesimals G. Duchêne - Structure Formation in the Universe - May 2007

  50. Perspectives • More observations will come with future instrumentation (e.g., ALMA) • At this stage, we still need • Complex modeling/analysis of datasets • More multi-technique analysis • Tests of the basic processes in models • Wait for next talks, to get the theorists’ point of view! G. Duchêne - Structure Formation in the Universe - May 2007

More Related