1. Disk evolution and Clearing P. D’Alessio (CRYA) C. Briceno (CIDA) J. Hernandez (CIDA & Michigan) L. Hartmann (Michigan) J. Muzerolle (Steward) A. Sicilia-Aguilar (Heidelberg) Spitzer/IRS disk modeling team L. Allen (SAO) T. Megeath (SAO) K. Luhman (PenState) N. Calvet (Michigan) T. Bergin (Michigan) D. Wilner (SAO) C. Qi (SAO) L. Adame (UNAM) C. Espaillat (Michigan) Z. Zhu (Michigan) R. Franco-Hernandez (SAO/UNAM)

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

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

4. Dust Spheres of size a with n(a) da = C a -p da, a min, a max a min = 0.005  m, p=2.5,3.5 a max =0.1  m – 1 cm Silicates, organics, amorphous carbon, water ice, troilite As a max increases: 1  m 10 mm 10 cm Less optical-nearIR opacity Higher mm opacity

5. Dust properties from SED Median SED of Taurus a max =0.3  m, ISM a max = 1mm D’Alessio et al 2001 a max increases,  1  decreases, less heating, less IR emission  mm increases, higher fluxes

6. Disks are accreting Inner disk is truncated by stellar magnetic field at ~ 3-5 R*. Matter flows onto star following field lines – magnetospheric accretion flow Hartmann 1998

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

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

9. Optically thin disks (debris disk) Furlan et al 2006 Chen et al 2006

10. 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

11. Questions How does gas evolve – dissipate? How does dust evolve – formation of large bodies? Characteristic times scales Compare characteristic properties of populations of different ages

12. Mass accretion rate decreases with time Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005) Fraction of accreting objects decreases with time.50.23.12 Viscous evolution - Gas

13. Accretion at 20 Myr: St34 Binary of two M3 stars Accreting No Li I absorption => old age Disk tidally truncated at 0.7AU Oldest accreting disk so far White & Hillenbrand 2005 Hartmann et al 2005

14. Dust emission decreases with age SEDs of stars in Tr 37 ~ 3 Myr IRAC data Weaker than median of Taurus Taurus median Phot Sicilia-Aguilar et al 2005

15. Fraction of optically thick inner disks decrease with age Decrease of fraction of objects with near-IR emission with age Near-IR from inner, hotter disk life-time ~ 5 Myr large scatter Hillenbrand, Carpenter, & Meyer 2006

16. Evolution of grains in disks As disk ages, dust growths and settles toward midplane as expected from dust evolution theories Weidenschilling 1997 Upper layers get depleted t = 0 Population of big grains at midplane

17. Dust evolution effects on SED Decrease of dust/gas in upper layers Weidenschilling 1997 Lower opacity, less heating, less emission D’Alessio et al. 2006  Increasing depletion of upper layers

18. Settling of dust toward midplane Furlan et al. 2005 Depletion of upper layers:  upp /  st

19. Settling of dust toward midplane Depletion of upper layers:  upp /  st Median of Taurus from IRAC fluxes for 60 stars (Hartmann et al 2005) and IRS spectra of ~75 objects (Furlan et al 2005)  ~ 0.1 – 0.01 Olivines Furlan et al 2006

20. Settling of dust toward midplane: small grains in upper layers Sargent et al 2006 Silicate emission feature formed in hot upper disk layers Small grains in upper layers Crystalline components

21. Crystallinity increases with degree of settling Sargent et al 2006 Watson et al 2006

22. SED evolution Taurus 1-2 Myr Tr 37 3 Myr NGC 7160 10 Myr Evolution of the median SED from IRAC and MIPS 24 measurements: Gradual decrease of emission, increased settling Sicilia-Aguilar et al 2005 Not the end of the story Fraction of inner disks decreases with time

23. Transitional disks Calvet et al 2002 TW Hya 10 Myr old Taurus median

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

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

26. More disks in transition in Taurus Calvet et al 2005 R w ~ 24AU outer disk + inner disk with little dust + gap (~ 5-24AU) R w ~ 3 AU only external disk but accreting star IRS spectra finely maps wall region

27. Detection of predicted hole on GM Aur with SMA Wilner et al 2006 R w ~ 24AU

28. Transition disks in Chamaeleon Espaillat et al 2006 R w ~ 9 AU Only external disk Accreting star Large grains

29. Inner disk clearing Search of transitional disks in large populations: IRAC-MIPS 24 observations of clusters and associations in a range of ages Photospheres Optically thick disks (Allen et al 2004) Transitional disks Muzerolle et al 2005

30. Inner disk clearing Observations of transition disks in populations of ages 1-10 Myr Indicate <10% t<1 Myr, ~ 10% few Myr timescale ~ N transition /N total x age ~ few 10 5 yrs  Rapid phase Accretion onto star is turned off quickly during transition phase (most objects not accreting) for ages > 3 Myr But in Taurus, most transitional disks accreting Constraints for models

31. Inner disk clearing: photoevaporation of outer disk? UV radiation photoevaporates outer disk When mass accretion rate (decreasing by viscous evolution) ~ mass loss rate, no mass reaches inner disk R g ~ G M * / c s 2 (10000K) ~ 10 AU (M * /M sol ) Evolution with photoeva poration Evolution without photoeva poration RgRg Clarke et al 2001

32. 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 and DM Tau Clarke et al 2001

33. Transitional Disk in a Brown Dwarf Muzerolle et al 2005 Model: Lucia Adame No significant UV R w = 1AU

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

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

36. Summary Great progress in understanding disk evolution Spitzer data crucial Disks evolve accreting mass onto star and dust growing and settling to midplane; phase can last at least ~ 20 Myr At some point, disk enters into transitional phase, turning off accretion and clearing up inner disk fraction of transitional disks increases with time but stabilizes to ~ 10 % after ~ 4 Myr low proportion of accreting transitional disks at >4 Myr 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

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

38. Giant planet formation theories Phase 1: Runaway accretion of solids (crossing of planetesimal orbits) stops when feeding zone depleted Phase 2:Accretion of gas Phase 3: Runaway accretion of gas Several timescales Phase 2 shorter if migration included – feeding zone not depleted (Alibert et al 2004) Many parameters involved – general idea of physical processes Pollack et al. 1996 1 2 3 solids gas total

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

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

41. Dust emission decreases with age Calvet et al. 2005 Taurus, 1-2 Myr Ori OB1b, 3-5 Myr

42. Settling of solids towards the midplane: effects on SED Furlan et al 2005 Depletion of upper layers:  upp /  st  = 0.001  =1 Model slopes for a range of  and inclinations compared to measured slopes in IRS spectra of Taurus stars Consistent with 1-0.1% depletion