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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?.

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slide1

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

Lee Hartmann

University of Michigan

what do we want to know
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
slide3

disk masses ≈ dust masses

measure here,

“optically thin”

star

disk

disk masses from dust emission
Disk masses from dust emission

850m fluxes (Taurus)

Protostars

accreting

Andrews & Williams 2005

median MINIMUM mass (100x dust) ≈ 10 M(J)

slide5

Caveat: other regions (e.g., Orion Nebula Cluster) may show systematically smaller “disk” masses

(outer disk...)

Eisner et al. 2008

slide6

However:

  • The dust opacity problem
  • maybe – the “where” problem
the dust opacity 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

usual value

spectral index

X

Mie calculation for power-law size distribution to a(max); D’Alessio et al. 2001

the dust opacity problem1
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

slide9

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

slide10

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

slide11

“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

slide12

Grain growth for mm-wave emission but not at 10 mm ⇒ upper layers have small dust

“ISM”

big grains

D’Alessio et al. 2001

slide13

Scattered light images – must be some growth/settling, otherwise disks are too “fat”

Stapelfeldt et al

D’Alessio et al. 2001

dust evolution
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)

slide15

Disks flatten with age

Sicilia-Aguilar et al. 2009

slide16

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

slide17

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

slide18

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* )

slide19

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

mass accretion rate decreases with time
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

why do t tauri stars accrete turbulence
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)
slide22

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)

slide23

Magnetic fields in disks?

Cold jets driven by accretion energy

280 AU

Burrows et al.

Calvet 1998

slide24

~ 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.

slide25

T Tauri outflows...

low-velocity wind; photoevaporation?

high-velocity wind

accretion rate →

Hartigan et al. 1995

slide27

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

slide28

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

slide29

Model vs. observation: ridiculous comparison or important suggestion?

model for FU Ori outbursts @ 1 Myr

slide30

“Dead zone” (Gammie 1996)

Difficult to explain FU Ori outburst without something like a massive dead zone at ~ 1 AU

slide31

Zhu et al. 2009 model w/dead zone

MRI?

Comparison with Desch reconstruction of solar nebula from “Nice” model

slide32

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

pre transitional disk lkca 15 gap
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

slide34

“Transition/evolved disk” timescale?

≈ 15% of “primordial” disks in Taurus ⇒ < 1 Myr

Luhman et al. 2009 (inconsistent with Currie et al. 2009)

slide35

Fl →

l→

“Transition” disks; difficult to detect if the gap/hole is not large (~ 3x in radius)

We are probably missing many gaps

slide36

LkCa 15; CO not double-peaked; distributed in radius

V836 Tau: CO double-peaked; outer truncation (?)

Najita, Crockett, & Carr 2008

slide37

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
slide38

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...
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