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Protoplanetary disk evolution and clearing

Protoplanetary disk evolution and clearing. Nuria Calvet (Michigan). K. Luhman (PennState) T. Megeath (Toledo) Michigan : T. Bergin L. Hartmann J. Hernandez C. Espaillat Z. Zhu L. Ingleby J. Tobin. Paola D’Alessio (CRYA) J. Muzerolle (Steward) C. Briceno (CIDA)

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Protoplanetary disk evolution and clearing

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  1. Protoplanetary disk evolution and clearing Nuria Calvet (Michigan) K. Luhman (PennState) T. Megeath (Toledo) Michigan: T. Bergin L. Hartmann J. Hernandez C. Espaillat Z. Zhu L. Ingleby J. Tobin Paola D’Alessio (CRYA) J. Muzerolle (Steward) C. Briceno (CIDA) A. Sicilia-Aguilar (MPI) L. Adame (UNAM) IRS disk modeling team L. Allen (SAO) D. Wilner (SAO) C. Qi (SAO) R. Franco-Hernandez (SAO)

  2. Disk evolution and Clearing • Disks evolve from optically thick dust+gas configurations to mostly solids debris disks HK Tau, Stapelfeldt et al. 1998

  3. Optically thick disks (T Tauri phase) Photosphere Furlan et al 2006 • optically thick dust+gas configurations, formed in the collapse of rotating molecular cores • dust/gas ~ 0.01 • heated by stellar radiation captured by dust (and viscous dissipation) • dust reprocesses heat and emits at IR • collisions transfer heat to gas, determines scale height • accreting mass onto the star

  4. Optically thin disks (debris disk) Chen et al 2006 • dust/gas ~ 0.99 • small secondary dust, from collisions of large bodies • large inner holes, tens of AUs • no gas accretion

  5. Questions • How does gas evolve – dissipate? • How does dust evolve – formation of large bodies? • Characteristic times scales

  6. Disks are accreting Excess energy over photospheric flux which cannot be accounted for by stellar energy Potential energy of matter accreting onto star Accretion from disk (where most of the mass of the molecular cloud core was deposited)

  7. Disks are accreting Inner disk is truncated by stellar magnetic field (~ KG, Valenti & Johns-Krull papers) at ~ 3-5 R*. Matter flows onto star following field lines – magnetospheric accretion flow Hartmann 1998

  8. Evidence for magnetospheric accretion Broad emission lines Muzerolle et al. 1998, 2001 Excess emission/veiling v ~ 250 km/s v ~ 0 km/s velocity

  9. Evidence for magnetospheric accretion Broad emission lines Muzerolle et al. 1998, 2001 Excess emission/veiling Calvet & Gullbring 1998 v ~ 250 km/s v ~ 0 km/s Redshifted absorption if right inclination

  10. Accretion luminosity and mass accretion rate Excess emission over photosphere ~ Lacc = G M (dM/dt) / R Gullbring et al. (1998) Ingleby et al 2007 Link to disk properties STIS data

  11. Present picture of inner disk Near-IR emission mostly from wall at dust destruction radius

  12. Emission from Wall at dust destruction radius • Emission ~ Black-body at T ~ 1400K, ~ vertical wall frontally illuminated • Increases with accretion luminosity, T ~ 1400K at larger radius • Rd (L* + Lacc ) 1/2 • Consistent with Lacc determinations Muzerolle et al 2003

  13. Accretion luminosity and mass accretion rate • Measure dM/dt for populations ~ 1 - 10 Myr • UV excess or excess at U (calibrated to Lacc) • Intrinsic chromospheric emission prevents measurement of low accretion luminosity • Model Ha line profiles to get mass accretion rate (Muzerolle papers) • Basis of all calibrations to obtain mass accretion rates for weak accretors (ie, brown dwarfs, “weak” TTS) • Uncertainties: temperature structure, geometry, effects of winds (Alencar et al . 2006; Kurosawa et al 2006)

  14. Mass accretion rate decreases with time Viscous evolution - Gas Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005)

  15. Viscous evolution S(R) decreases with time Disk expands Region of dM/dt ~ const, S ~ 1/R Models for steady disks Irradiated accretion disks (D’Alessio models) using dM/dt onto star (from UV) S(R) given dM/dt determined from UV for each object (not a free parameter) Hartmann et al. (1998)

  16. Irradiated steady accretion disks • Irradiated (steady) accretion disks (D’Alessio models) • S(R)given observed dM/dt • S ~ (dM/dt) / a • Uncertainty in a • Mdisk ~ S x size, a “calibrated” by measurement of disk mass • Uncertainty in mass determination – dust opacity, multiwavelength observations to constrain dust mixture • If MRI, then layered accretion (Gammie 1996), dead zone • Photoevaporation (Clarke et al 2001)

  17. High accretors: FU Ori Inner disk: standard accretion disk dM/dt ~ 10-4 Msun/yr Instability region ~ 0.6 AU, >> Bell & Lin 1994 Flared outer disk irradiated by inner disk Zhu et al 2007

  18. High accretors: DR Tau Silicate emission and high far-IR flux because of irradiation by high energy radiation from accretion shock viscous wall dM/dt = 2 e-7 Msol/yr D’Alessio et al 2007

  19. High accretors at 5 Myr Orion OB1b sample (Hernandez e al 2007)

  20. Mass accretion rate decreases with time Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005) .50 .23 .12 Fraction of accreting objects decreases with time: not explained by viscous evolution: dust evolution?

  21. Dust properties from SED: Grain growth Median SED of Taurus amax = 1mm amax=0.3mm, ISM D’Alessio et al 2001 amax increases, k1m decreases, less heating, less IR emission kmm increases, higher fluxes

  22. Evolution of grains in disks • As disk ages, dust growths and settles toward midplane t = 0 Population of big grains at midplane Upper layers get depleted Weidenschilling 1997 Dullemond and Dominik 2004

  23. Settling of solids: TW Hya 3.5 cm flux ~ constant=> Dust emission Wilner et al. 2005 Jet/wind? Nonthermal emission?

  24. Settling: bimodal grain size distribution Wilner et al. 2005 Small + 5-7mm Weidenschilling 1997 S ~ 1/R

  25. Dust evolution effects on SED Decrease of dust/gas in upper layers Lower opacity, less heating, less IR emission, but silicate emission Increasing depletion of upper layers z D’Alessio et al. 2006 Dullemond & Dominik 2004; Lada et al 2006 Weidenschilling 1997

  26. Spitzer/IRS data of Taurus (1-2 Myr) Large range of properties at one age Furlan et al. 2006

  27. Settling of dust toward midplane Furlan et al 2006 Median of Taurus from IRAC fluxes for 60 stars (Hartmann et al 2005) and IRS spectra of ~75 objects (Furlan et al 2005) Depletion of upper layers: upp/st Upper laters depleted by 10 to 1% of standard dust-to-gas ratio D’Alessio et al 2006

  28. Settling of dust toward midplane: small grains in upper layers • Silicate emission feature formed in hot upper inner disk layers • Small grains in upper layers, consistent with settling • Crystalline components Sargent et al 2006

  29. SED evolution:comparison at different ages IRAC data for a number of clusters and associations with ages 1 – 10 Myr: Gradual decrease of excess emission [3.6] – [4.5] Data from Hartmann et al 2005 Sicilia-Aguilar et al 2005 Lada et al 2006 Hernandez et al 2007b Taurus Hernandez et al 2007

  30. SED evolution: inner disk Decrease of median slope with age: consistent with decrease of dM/dt and dust settling in inner disk Photosphere Hernandez et al 2007b

  31. Art by Luis Belerique & Rui Azevedo SED evolution Slope becomes stepper - less excess as Degree of settling increases wall Accretion rate decreases disk log dM/dt= -10, -9, -8, -7 S decreases

  32. Taurus 1-2 Myr Tr 37 3 Myr NGC 7160 10 Myr SED evolution Evolution of the median SED from IRAC and MIPS 24 measurements: Faster evolution of inner disk Sicilia-Aguilar et al 2005

  33. SED evolution Present evidence: As a given population ages, the fraction of remaining disks tend to have lower accretion rates and their dust more settled toward the midplane But fraction of remaining disks decreases with time. What happened to the other disks?

  34. Transition disks • Transition disks? • Lack of significant excess flux below 10 mm • But flux comparable to the median of Taurus at longer wavelengths • Model: • Clearing of the innermost, hotter disk regions • Truncated outer optically thick disk • Wall at truncation radius illuminated frontally by star

  35. Transition disks TW Hya 10 Myr old Taurus median • Near to mid-IR flux deficit • Sharp rise • Flux at longer l consistent with optically thick emission Calvet et al 2002

  36. Inner disk clearing Spectra from IRS on board SPITZER TW Hya, ~ 4 AU ~ 10 Myr Wall Optically thick outer disk Optically thin region with lunar mass amount of micron size dust + gas (accreting star) Inner disk Uchida et al. 2004

  37. T=150-85 K 4 AU td Inner disk clearing CoKu Tau 4, ~ 10 AU ~ 2 Myr No inner disk, silicate from wall atmosphere Non-accreting star Forrest et al. 2004; D’Alessio et al. 2005

  38. More disks in transition in Taurus Rw ~ 24AU outer disk + inner disk with little dust + gap (~ 5-24AU) Inner disk Rw ~ 3 AU only external disk but accreting star Calvet et al 2005

  39. Transition Disk in a Brown Dwarf Rw = 1AU Muzerolle et al 2006

  40. Evolving transition disks: grain growth Micron-size grains in optically thin inner disk and wall ISM Rw = 47AU Ne II line, enhanced penetration of X-rays Espaillat et al 2007

  41. Inner disk Substantial mass accretion rates and high mm fluxes in GM Aur, DM Tau, TW Hya CO emission in inner disk of TW Hya (Rettig et al 2004) H2 emission from inner disk of GM Aur, DM Tau, TW Hya in FUV spectra (Bergin et al 2004) Ne II, X-ray induced ionization (Espaillat et al 2007, following ionization model Glassgold et el 2007)

  42. Inner disk clearing: photoevaporation of outer disk? Evolution with photoevaporation UV radiation photoevaporates outer disk When mass accretion rate (decreasing by viscous evolution) ~ mass loss rate, no mass reaches inner disk Rg ~ G M* / cs2(10000K) ~ 10 AU (M*/Msol) Rg Evolution without photoevaporation Clarke et al 2001

  43. Inner disk clearing:photoevaporation of outer disk? Prediction: low mass accretion rate and mm flux in transitional disks But average mass accretion rates and high mm fluxes in GM Aur , DM Tau, TW Hya Clarke et al 2001

  44. Inner disk clearing: photoevaporation of outer disk? • Increasing hole sizes with mass • High disk masses and accretion rates • Transition disks in brown dwarfs (Muzerolle et al 2006)  No significant UV flux • Inner disk

  45. Inner disk clearing: planet(s)? Giant planet forms in disk opening a gap Wall of optically thick disk = outer edge of gap at a few AU Bryden et al 1999 Inner gas disk with minute amount of small dust – silicate feature but little near IR excess, bigger bodies may be present

  46. Inner disk clearing: planets? • Tidal truncation by planet • Hydrodynamical simulations+Montecarlo transfer – SED consistent with hole created and maintained by planet – GM Aur: ~ 2MJ at ~ 2.5 AU – Rice et al. 2003 SED depends on mass of planet (and Reynolds number) 21 MJ 1.7 MJ 0.085 MJ 43 MJ

  47. Inner disk clearing: planets? CoKu Tau 4, wall at ~ 10 AU No inner disk Planet-disk system with planet mass of 0.1 Mjup for CoKu Tau 4 Quillen et al. 2004 D’Alessio et al. 2005 Long term duration of system?

  48. Inner disk clearing: planets? • Planet formation can explain: • SEDs of transition disks • short timescale for transition phase ~ run-away gas accretion/gap opening • rapid disappearance of inner disk, viscous time scale at • gap, increased efficiency of MRI in low opacity inner disk • Problems: outer disk may make planet migrate inwards in viscous timescale, small a? • Recurrent events? • High accretors at advanced ages?

  49. Summary • Space data crucial for progress in understanding disk evolution • Disks gradually evolve accreting mass at decreasing rates onto star while dust grows and settles toward midplane • At some point, disk enters into transition phase, eventually turning off accretion and clearing up inner disk • Alternative models for clearing are planet formation and photoevaporation of outer disks. Present evidence may favor planet formation • Need characterization of properties of transitional disks in large samples of different ages plus theoretical efforts

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