Protostellar/planetary disk observations (and what they might imply)

1. Protostellar/planetary disk observations (and what they might imply) Lee Hartmann University of Michigan

2. What do we want to know? • What are disk masses? • How is the mass distributed? • Is there “turbulence”? What is it like? where does it occur? • What transport processes are operating? • I’ll talk about observations instead... • dust mass estimates • disk structure • time-dependence

3. disk masses ≈ dust masses measure here, “optically thin” star disk

4. Disk masses from dust emission 850m fluxes (Taurus) Protostars accreting Andrews & Williams 2005 median MINIMUM mass (100x dust) ≈ 10 M(J)

5. Caveat: other regions (e.g., Orion Nebula Cluster) may show systematically smaller “disk” masses (outer disk...) Eisner et al. 2008

6. However: • The dust opacity problem • maybe – the “where” problem

7. The dust opacity problem Observed spectral slopes imply that dust must grow from ISM sizes; if growth is does not stop at ~ few cm, opacities are LOWER than typically adopted – disk masses are then larger than usually estimated usual value spectral index X Mie calculation for power-law size distribution to a(max); D’Alessio et al. 2001

8. The dust opacity problem “Clint Eastwood question”: do we feel lucky? (especially in outer disk) usual value D’Alessio et al. 2001 Dominik & Dullemond 05

9. Where is the mass? usual MMSN ? Conventional models (MMSN) yield S ∝ R –p , p ~ 1.5 - 0.4, <p> ~ 0.8: ⇒ most mass at large R Best we can do: however, (1) no k(R) (2) can’t resolve and/or limit R< 10 AU because of optical depth Andrews et al. 2009

10. Disk accretion: statistical measure of gas dM/dt x 106 yr = 0.1M* Calvet et al. 2004, Muzerolle et al. 2003, 2005, White & Ghez 2001, White & Basri 2003, Natta et al 2004 submm <Md> / 106 yr ⇒ masses from dust emission may be underestimates

11. “large” dust (≥1mm); H = ?? Protostellar/planetary disks (~ few Myr) flared disk surface, “small” (~ 1μm) dust, ~3-5H optically thick to stellar radiation not expected; turbulence?? as expected

12. Grain growth for mm-wave emission but not at 10 mm ⇒ upper layers have small dust “ISM” big grains D’Alessio et al. 2001

13. Scattered light images – must be some growth/settling, otherwise disks are too “fat” Stapelfeldt et al D’Alessio et al. 2001

14. Dust evolution Models for:  (depletion of small dust = 1 0.1 0.01 0.001 Depletion < 0.1% in inner disk upper layers after 5 Myr (Hernandez & IRAC disk team, 2007)

15. Disks flatten with age Sicilia-Aguilar et al. 2009

16. some correlation of disappearance of silicate feature with less “flared” disk; grain growth/settling; depletions of small dust ≈ 10-1 – 10-3 (good for MRI?) changes in crystallinity (Bouwman, Sargent et al.) less flared Watson, IRS disk team, 2009 Furlan et al. 2006

17. Disk “frequency” (small dust < 10 AU) decreases over few Myr disk clearing timescales range over an order of magnitude ⇒ initial conditions ⇒ angular momentum Hernandez et al. 2007

18. Disk frequencies decrease rapidly above 1 M Lada et al. 2006 Disk evolution timescales much faster at higher masses (consistent with dM/dt increasing with M* )

19. not much known about gas content; inner disk gas not detected (warm CO ro-vib transitions) in disks without near-IR dust emission Najita, Carr, Mathieu 2003 no CO 2mm emission However accretion stops when the near-IR excess disappears IR excess

20. Mass accretion rate decreases with time Viscous evolution model Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005) .50 .23 .12 Fraction of accreting objects decreases with time

21. Why do T Tauri stars accrete? turbulence? • Inner disk (< 0.1 AU) – dust evaporated, ionized, MRI • beyond? MRI active layers (Gammie)? • why the dM/dt vs. M* dependence? may work... • if dust settling needed to maintain ionization... why not more variable? why not any apparent dependence on SED? • GI until dust evaporation? (e.g. Rice & Armitage)

22. X-ray or EUV heating?... (ionization) Pascucci et al. 2007 Espaillat et al. 2007 CO J=6-5 in TW Hya; may also need X-ray heating (Qi et al. 2006)

23. Magnetic fields in disks? Cold jets driven by accretion energy 280 AU Burrows et al. Calvet 1998

24. ~ 0.1 AU 280 AU Coffey et al. 2007; high-v jet from 0.2-0.5 AU low-v flow from < 2 AU... but indirect argument Burrows et al.

25. T Tauri outflows... low-velocity wind; photoevaporation? high-velocity wind accretion rate → Hartigan et al. 1995

26. Most of the stellar mass is accreted in the protostellar phase - from disks! - in outbursts?

27. FU Ori objects: ~ 0.01 M(sun) accreted in ~ 100 years; unlikely to be accreted from 100 AU in this time ⇒ large lump of material at ≈ few AU, at least in protostellar phase Ibrahimov

28. Zhu et al. 2008, 2009; dead zone + active layer; outbursts during infall to disk (also Armitage et al. 01, Vorobyov & Basu 05,6,7,8) M* Mdisk

29. Model vs. observation: ridiculous comparison or important suggestion? model for FU Ori outbursts @ 1 Myr

30. “Dead zone” (Gammie 1996) Difficult to explain FU Ori outburst without something like a massive dead zone at ~ 1 AU

31. Zhu et al. 2009 model w/dead zone MRI? Comparison with Desch reconstruction of solar nebula from “Nice” model

32. Inner disk holes: consequence of very rapid inner disk accretion? Hughes et al. 2009 Calvet et al. 2005 TW Hya D’Alessio et al. 2005

33. Pre-Transitional Disk LkCa 15:Gap? median Taurus SED = optically thick full disk outer radius ≈ 40 AU? photosphere large excess, ~optically thick disk Increasing flux/ optically thick disk Espaillat & IRS team, 2007

34. “Transition/evolved disk” timescale? ≈ 15% of “primordial” disks in Taurus ⇒ < 1 Myr Luhman et al. 2009 (inconsistent with Currie et al. 2009)

35. Fl → l→ “Transition” disks; difficult to detect if the gap/hole is not large (~ 3x in radius) We are probably missing many gaps

36. LkCa 15; CO not double-peaked; distributed in radius V836 Tau: CO double-peaked; outer truncation (?) Najita, Crockett, & Carr 2008

37. Irresponsible speculations • Disks must generally be massive at early times. Unless MRI is much more effective than we now think, ⇒ pileup of mass, especially in inner disk • Pileup (aka “dead zone”) is attractive! • explains FU Ori outbursts • helps explain “luminosity problem” of protostars (accretion rate onto protostar < infall rate; Kenyon et al 1990,94; Enoch et al. 2009) • dM/dt(infall) > dM/dt(accretion) helps to make disk evolution more strongly dependent upon initial angular momentum ⇒ variation of disk evolutionary lifetimes • more mass to make super Jupiters in the inner disk • more mass to throw away or accrete • potentially useful effects on migration • Minus; direct detection in dust emission not currently feasible, but does not contradict current observations... ALMA

38. summary of disk observations • Disk frequencies (dust emission) not very different from 3m ⇒ 24m  evolution similar from 0.1 to ~ 10 AU • decay time ≈ 3 Myr (but varies by 10x) • Gas accretion ceases as IR excess disappears- clearing of inner disk • T Tauri stars accrete ~ MMSN (gas) during their lifetimes; why? • Small dust in upper disk layers: turbulent support? • Evidence for dust settling/growth, increasing with age (depletions ~ 0.1-0.001); also X-ray and/or EUV heating in uppermost disk layers • “Transitional disks (holes, gaps)” ~10% @ 1-2 Myr • Who knows what is happening at 1 AU @ 1 Myr (optically-thick, not spatially-resolved) • Disk masses may be systematically underestimated  room for mass loss (migration, ejection) • Massive inner disks? needed to explain FU Ori outbursts...