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Models of Disk Structure, Spectra and Evaporation

Models of Disk Structure, Spectra and Evaporation. Kees Dullemond, David Hollenbach, Inga Kamp , Paola D’Alessio. Disk accretion and surface density profiles Vertical structure models and SEDs Gas models and disk surface layers Evaporation by the central star .

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Models of Disk Structure, Spectra and Evaporation

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  1. Models of Disk Structure, Spectra and Evaporation Kees Dullemond, David Hollenbach, Inga Kamp, Paola D’Alessio • Disk accretion and surface density profiles • Vertical structure models and SEDs • Gas models and disk surface layers • Evaporation by the central star

  2. Why study the structure of protoplanetary disks? Disk structure models are the backbone of planet formation models • Core accretion versus gravitational instability ? • What is the fraction of disks that can form planets ? • dust settling, growth and planetesimal formation depend on gas-dust dynamics

  3. Overview • Accretion determines the surface density as a function of radius: typical accretion rates are dM/dt~10-8 M/yr S ~ R-1

  4. Accretion and radial disk structure Formation of the disk...

  5. Accretion and radial disk structure Mass accretion

  6. Accretion and radial disk structure Angular Momentum transport

  7. Accretion and radial disk structure Viscous spreading of the disk... ... while disk loses mass by accretion

  8. Accretion and radial disk structure Viscous spreading of the disk... ... while disk loses mass by accretion

  9. Accretion and radial disk structure Viscous spreading of the disk... ... while disk loses mass by accretion onto star Mass reservoir of the disk, which feeds the inner disk regions

  10. Accretion and radial disk structure Viscous spreading of the disk... ... while disk loses mass by accretion Semi-stationary region, with mass supply from outer reservoir

  11. Brief history of a star and a disk After: Hueso & Guillot 2005 (Lynden-Bell & Pringle; Hartmann et al. ; Nakamoto & Nakagawa)

  12. Actively accreting irradiated disks Solid line: Hueso & Guillot (2005) Dashed line: D’Alessio et al. (2001) • ~ R-1.5 (MMSS) S ~ R-1 -profile clearly shallower than ‘Minimum mass solar nebula’ • Very young disk (accretion-heating dominated): ~R-0.5. • T Tauri disk (irradiative heating dominates outer disk): ~R-1

  13. Overview • Accretion determines the surface density as a function of radius: typical accretion rates are dM/dt~10-8 M/yr S ~ R-1 • Vertical structure models predict SEDs: disks are flared disks possess an inner rim (dust evaporation radius)

  14. SEDs of intermediate-mass stars Group I Group II AB Aurigae (Group I) HD104237 (Group II) SEDs of intermediate-mass stars Group I Group II Classification of Meeus et al. 2001 (Note: not to be confused with class 0,I,II,III of the Lada et al classification!)

  15. Fitting pure accretion disk models... AB Aurigae (Group I) HD104237 (Group II) Group I: Bad fit at >10 micron. Group II: Reasonable fit (though need high accretion rate). (Hillenbrand 1992; Rucinski 1985; Adams et al. 1988; Bertout et al. 1988; Bell et al. 1997; Lynden-Bell 1969; Lynden-Bell & Pringle 1974)

  16. Fitting irradiated disks... AB Aurigae (Group I) HD104237 (Group II) Group I: Reasonable fit for overall flat SED. Group II: SED tends to be too flat (Kenyon & Hartmann 1987; Chiang & Goldreich 1997; D’Alessio et al. 1998, 1999; Lachaume et al. 2004)

  17. Dust evaporation: (puffed-up) inner rim... AB Aurigae (Group I) HD104237 (Group II) All sources: Dust inner rim might solve the NIR problem Group II: Still not well fitted at >10 micron (Natta et al. 2001; Tuthill et al. 2001; Dullemond et al. 2001; Muzerolle et al. 2003; Isella & Natta 2005; Akeson et al.; Monnier et al. ; Eisner et al.; Millan-Gabet et al.)

  18. Reducing somehow the far-IR flux... AB Aurigae (Group I) HD104237 (Group II) Group II: Outer disk height can be reduced by e.g. dust settling (D’Alessio et al. 1999; Chiang et al. 2001). Disk might be shadowed (Dullemond & Dominik 2004b), but this is still under debate(Walker et al. 2006)

  19. Irradiated surface & visc. heated midplane Vertical structure of disk at 1AU: Viscous accretion heating dominates the disk midplane, while the surface layer temperatures are set by irradiation only 0.1 0.2 z [AU] D’Alessio et al. model

  20. SED of disk with hot surface layer After: Chiang & Goldreich 1997 Calvet et al. 1991; Malbet & Bertout 1991; Many 2D/3D RT papers

  21. Overview • Accretion determines the surface density as a function of radius: typical accretion rates are dM/dt~10-8 M/yr S ~ R-1 • Vertical structure models predict SEDs: disks are flared disks possess an inner rim (dust evaporation radius) • Tgas > Tdust in disk surface layers (tross <~ 1.0): gas and dust are not well coupled molecules can form

  22. Disk surface layers with PAHs no PAHs CTTS tross=1 HAe tross=1 Tgas = Tdust (Kamp & Dullemond 2004; Jonkheid et al. 2004; Nomura & Millar 2005; Kamp et al. 2005)

  23. Vertical cut at R = 9 AU Gas temperature is higher than dust temperature in the surface layers (Jonkheid et al. 2004, Kamp et al. 2004, Nomura & Millar 2005) Tevap:= GM*mmp/kr Tgas Tevap Tdust

  24. Vertical cut at R = 9 AU H2/H Molecules like H2, CO, OH etc. exist in these hot surface layers. Tgas Tevaporation Tdust

  25. Vertical cut at R = 9 AU H2/H CO/C/C+ Molecules like H2, CO, OH etc. exist in these hot surface layers. Tgas Tevaporation Tdust

  26. Vertical cut at R = 9 AU H2/H CO/C/C+ Gas temperature is set by the balance of photoelectric heating, H2 formation heating and OI, H2 line cooling. Below tross~1, gas-grain collisions thermalize the gas and dust. Tgas Tevaporation gas-grain collisions H2 formation PE heating Tdust

  27. Vertical cut at R = 9 AU H2/H CO/C/C + Gas temperature is set by the balance of photoelectric heating, H2 formation heating and OI, H2 line cooling. Below tross~1, gas-grain collisions thermalize the gas and dust. Tgas Tevaporation gas-grain collisions H2 formation PE heating gas-grain collisions Tdust H2 lines Lya cooling OI cooling

  28. Vertical cut at R = 9 AU H2/H CO/C/C + Tgas Tevaporation Tdust

  29. Vertical cut at R = 9 AU H2/H CO/C/C + Photoevaporation flow starts well below Tgas=Tevaporation (Adams et al. 2004) Tgas Tevaporation origin of the flow Tdust

  30. Overview • Accretion determines the surface density as a function of radius: typical accretion rates are dM/dt~10-8 M/yr S ~ R-1 • Vertical structure models predict SEDs: disks are flared disks possess an inner rim (dust evaporation radius) • Tgas > Tdust in disk surface layers (tross <~ 1.0): gas and dust are not well coupled molecules can form • Disk dispersal can proceed via photoevaporation by the FUV/EUV of the central star: FUV evaporation proceeds from outside in

  31. Stellar EUV and FUV EUV FUV

  32. Photoevaporation by the central star viscous accretion rcrit rcrit rcrit = 12 (M*/1M) (103 K/Tgas) AU Need to self-consistently calculate the chemistry, heating and cooling, radiative transfer, vertical and radial structure, and dynamics of flow. Approximations are made ! (Adams et al. 2004; Gorti & Hollenbach 2005)

  33. Disk evaporation by FUV photons timescale Evaporation for various central stars: Disk survival times peak at ~ 1 M (Gorti & Hollenbach) T Tauri star: Mgas = 0.03 M*, S ~ R-1, Rout = 200 AU Disk evaporates outside in  Poster 291

  34. Additional Applications of Evaporation • Rapid transition from classical T Tauri to weak-line T Tauri stars: • EUV photoevaporation opens a gap at rcrit at a timescale of ~ 1 Myr •  mass supply from outer disk gets cutoff • inner disk accretes onto the star on a timescale ~105 yr • (Clarke et al. 2001), (Alexander et al. 2005)  poster 292

  35. Additional Applications of Evaporation • Formation of planetesimals: • dust settling lowers the dust:gas ratio (Mdust/Mgas) in disk surfaces •  dust-depleted evaporation flows and dust settling leave the • midplane behind with high Mdust/Mgas (Throop & Bally 2005) •  midplane can become gravitational instable (Youdin & Shu 2002) •  spontaneous formation of km-sized planetesimals

  36. Summary • Accretion determines the surface density as a function of radius: typical accretion rates are dM/dt~10-8 M/yr S ~ R-1 • Vertical structure models predict SEDs: disks are flared disks possess an inner rim (dust evaporation radius) • Tgas > Tdust in disk surface layers (tross <~ 1.0): gas and dust are not well coupled molecules can form • Disk dispersal can proceed via photoevaporation by the FUV/EUV of the central star: FUV evaporation proceeds from outside in

  37. Schematic view of protoplanetary disks Dust

  38. Schematic view of protoplanetary disks Gas

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