Presentation on theme: "Protostellar/planetary disk observations (and what they might imply) Lee Hartmann University of Michigan."— Presentation transcript:
Protostellar/planetary disk observations (and what they might imply) Lee Hartmann University of Michigan
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? Ill talk about observations instead... dust mass estimates disk structure time-dependence
disk masses dust masses measure here, optically thin star disk
Disk masses from dust emission 850 m fluxes (Taurus) Andrews & Williams 2005 Protostars accreting median MINIMUM mass (100x dust) 10 M(J)
Caveat: other regions (e.g., Orion Nebula Cluster) may show systematically smaller disk masses Eisner et al. 2008 (outer disk... )
However: The dust opacity problem maybe – the where problem
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 Mie calculation for power-law size distribution to a(max); DAlessio et al. 2001 usual value X spectral index
The dust opacity problem Clint Eastwood question: do we feel lucky? (especially in outer disk) DAlessio et al. 2001 usual value Dominik & Dullemond 05
Where is the mass? Andrews et al. 2009 Conventional models (MMSN) yield R –p, p ~ 1.5 - 0.4, ~ 0.8: most mass at large R Best we can do: however, (1) no (R) (2) cant resolve and/or limit R< 10 AU because of optical depth
Disk accretion: statistical measure of gas Calvet et al. 2004, Muzerolle et al. 2003, 2005, White & Ghez 2001, White & Basri 2003, Natta et al 2004 dM/dt x 10 6 yr = 0.1M * submm / 10 6 yr masses from dust emission may be underestimates
Protostellar/planetary disks (~ few Myr) optically thick to stellar radiation large dust (1mm); H = ?? flared disk surface, small (~ 1μm) dust, ~3-5H as expected not expected; turbulence??
Grain growth for mm-wave emission but not at 10 m upper layers have small dust DAlessio et al. 2001 big grains ISM
Stapelfeldt et al Scattered light images – must be some growth/settling, otherwise disks are too fat DAlessio et al. 2001
Dust evolution (depletion of small dust = 1 0.1 0.01 0.001 Models for: Depletion < 0.1% in inner disk upper layers after 5 Myr (Hernandez & IRAC disk team, 2007)
Disks flatten with age Sicilia-Aguilar et al. 2009
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.) Furlan et al. 2006 less flared Watson, IRS disk team, 2009
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
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 * )
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 IR excess no CO 2 m emission However accretion stops when the near-IR excess disappears
Mass accretion rate decreases with time Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005) Viscous evolution model Fraction of accreting objects decreases with time.50.23.12
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)
X-ray or EUV heating?... (ionization) Pascucci et al. 2007Espaillat et al. 2007Espaillat et al. 2007 CO J=6-5 in TW Hya; may also need X-ray heating (Qi et al. 2006)
Calvet 1998 Magnetic fields in disks? Cold jets driven by accretion energy 280 AU Burrows et al.
280 AU Burrows et al. Coffey et al. 2007; high-v jet from 0.2-0.5 AU low-v flow from < 2 AU... but indirect argument
high-velocity wind accretion rate low-velocity wind; photoevaporation? Hartigan et al. 1995 T Tauri outflows...
Most of the stellar mass is accreted in the protostellar phase - from disks! - in outbursts?
Ibrahimov 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
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) Mdisk M*M*
Model vs. observation: ridiculous comparison or important suggestion? model for FU Ori outbursts @ 1 Myr
Dead zone (Gammie 1996) Difficult to explain FU Ori outburst without something like a massive dead zone at ~ 1 AU
Zhu et al. 2009 model w/dead zone Comparison with Desch reconstruction of solar nebula from Nice mode l MRI?
Inner disk holes: consequence of very rapid inner disk accretion? TW Hya Calvet et al. 2005 Hughes et al. 2009 DAlessio et al. 2005
Pre-Transitional Disk LkCa 15: Gap? large excess, ~optically thick disk median Taurus SED = optically thick full disk photosphere Increasing flux/ optically thick disk Espaillat & IRS team, 2007 outer radius 40 AU?
Transition/evolved disk timescale? 15% of primordial disks in Taurus < 1 Myr Luhman et al. 2009 (inconsistent with Currie et al. 2009)
Transition disks; difficult to detect if the gap/hole is not large (~ 3x in radius) We are probably missing many gaps F
LkCa 15; CO not double-peaked; distributed in radius V836 Tau: CO double-peaked; outer truncation (?) Najita, Crockett, & Carr 2008
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
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...