Infall and Rotation around Young Stars Formation and Evolution of Protoplanetary Disks Michiel R....

Infall and Rotation around Young Stars

Formation and Evolution of Protoplanetary Disks

Infall and Rotation around Young Stars

Formation and Evolution of Protoplanetary Disks

Michiel R. Hogerheijde

Steward Observatory

The University of Arizona

OutlineOutline

• An overview of star formation

• Rotation in interstellar clouds

• Decoupling of collapsing cores

• Formation of disks

• L1489 IRS: A transitional object with a contracting disk?

• Summary and further work

An overview of star formationAn overview of star formation

(Hogerheijde 1998; after Shu et al. 1987)

Cloud StructureCloud Structure

•Cloud complex•Filaments•Cores•Kernels

Motte & André (2001)

OutlineOutline







Rotation in interstellar cloudsRotation in interstellar clouds

• Line width – size relation

• Specific angular momentum – size relation

• Magnetic breaking

• Turbulence as a source of rotation


• v–R relation (Larson 1981)

Larson (1981)

vR0.5


• Line width – size relationship• vR, =0.530.07 (Caselli & Myers 1995)

• Virial equilibrium: 2K+W=0Mv2-GM2/R=0vR0.5

• Turbulent and/or rotational support for cloud cores


• J/M–R relation (Goodman et al. 1993)

• R-0.4

• ~ constant• J/M R1.6

Goodman et al. (1993)


€

Goodman et al. (1993): ω∝R−0.4

Define β≡rotational energy

gravitational energy∝

Iω2

GM2 /R∝ω2R3

GM, with moment of inertia I ≡pMR2

Goodman et al. find β ≈0.02

Specific angular momentum JM

=IωM

∝ωR2 ∝R1.6, using I ∝MR2 and ω∝R−0.4

If virial equilibrium applies, Δv2 =GM /R⇒ βvirial=ω2R2

Δv2 =ω2R∝R0 ≈constant

constant density, constant ω⇒ β constant

differential rotation ω∝R-1, n∝R−2 ⇒ β constant


• Magnetic breaking (Königl 1987; Mouschovias 1991)

Basu (1997)


• Turbulence as a source of rotation (Burkert & Bodenheimer 2000)

n=-4

n=-3

n=-2

Different realizations

p(k)~kn

J/M=2.310-3 km s-1 pc

=0.03, independent of R

Burkert & Bodenheimer (2000)

OutlineOutline







Decoupling of collapsing coresDecoupling of collapsing cores

• Goodman et al. (1998)• R>0.1 pc vR0.5

• R<0.1 pc vR0

• Transition to coherence

• Scale corresponds to clustering-scale of young stars in Taurus (Larson 1995)

(dramatization)Goodman et al. (1998)


• Ohashi et al. (1997)

• Two embedded YSOs in Taurus

• IRAS 04169+2702: rotating, flattened envelope; must be infalling too

• IRAS 04365+2535: compact core; could be rotationally supported

R~0.1 pc

Ohashi et al. (1997)


• Belloche et al. (2002)

• Deeply embedded YSO IRAM 04191+1521

• Outflow• Flattened envelope• Spectral signature of

infall• Position-velocity

diagram suggests rotation

Belloche et al. (2002)


• 1D model of infall

• ‘2D’ model of rotation

• Break at ~3300 AU (0.02 pc)

• Infall: constant inside-out

• Rotation: slow spin up

• Mass reservoir ~0.5 M

Belloche et al. (2002)

OutlineOutline







Formation of disksFormation of disks

• Terebey, Shu, & Cassen (1984; TSC84)

• Inside-out collapse: asound, t

• Slow rotation, solid body: Ω

• Centrifugal radius Rc asoundt3Ω2

• Initial growth of disk small (t<1)

• Rapid growth at late times (t>1): infall of material from large R with large ΩR


• Basu (1998)• Weak magnetic field• Magnetic breaking:

differential rotation ΩR-1

• Rc t Ω2

• Rapid initial growth• Later growth linear:

material at large R has smaller initial Ω

TSC84

Basu (1998)

Basu (1998)


• Stahler et al. (1994)

• Growth of disk in TSC84 framework

• 3 regions• Inner dense disk,

Keplerian, R<Rd

• Outer tenuous disk, rapid inflow, Rd<R<Rc

• Narrow dense ring where mass and angular momentum piles up, Rd≈0.34 Rc

Adapted from Stahler et al. (1994)


• Shear motions dissipated by viscosity

• Source of viscosity unknown; turbulence?

• viscosity: = asound H (Shakura & Sunyaev 1973)

• Stellar irradiation, viscosity sets up temperature distribution TR-1/2 R

• Resulting surface density distribution (R)= 0(R/R0)-1 (Lynden-Bell & Pringle 1974; Pringle 1981)

• Continued evolution: disk spreading while matter accretes onto star


• Vertical scale height H set by temperature• Increased angle of interception stellar light raises

temperature• Result: Flaring disk (e.g., D’Alessio et al. 1998;

Chaing & Goldreich 1997; Dullemond et al. 2001)

OutlineOutline







L1489 IRS: A transitional object with a contracting disk?


• L1489 IRS = IRAS 04016+2610

• Lbol=3.7 L embedded YSO

• Taurus, d~140 pc• Very weak outflow• HST/NICMOS:

inclined, cleared-out cavity (Padgett et al. 1999)

Padgett et al. (1999)



• SCUBA submillimeter continuum images, 850 and 450 µm

• Compact emission around star

• Extended starless core 8000 AU to north-east

Hogerheijde & Sandell 2000




Best-fit Shu (1977) parameters:asound=0.46±0.04 km s-1

t=(1.3–3.2)106 yrrCEW=130,000–300,000 AU >> core




‘Classic’ infall signatureCan fit collapse model to data,

but not for same (asound, t)




L1527 IRS‘Classic’ infall signatureWell fit for same (asound, t)




TMC1‘Classic’ infall signatureWell fit for same (asound, t)

Not a problem with the Shu (1977) inside

out collapse model



• BIMA and OVRO millimeter interferometer maps• HCO+ J=1–0 and 3–2• Resolution ~5=700 AU• Rotating disk, not infalling envelope• Radius ~2000 AU, >> typical disk around T Tauri stars

2000AU

Hogerheijde 2001



• Position–velocity diagrams look like Keplerian rotation

2800 0 -2800

0

2

-2

2

0

-2

Vel

ocit

y (k

m s

-1)

Offset (AU)

• Flared disk• Keplerian rotation around

M=0.65 M

• vin=1.3 (R/100 AU)-0.5 km s-1

• Mdisk=0.02 M (from SCUBA)

Hogerheijde 2001



• Interferometer and single-dish spectra reproduced• Including infall signature• Requires some foreground absorption in HCO+ 1–0

Hogerheijde 2001



• L1489:• Rotation>infall• Life time ≈2104 yr• Mdisk/ ≈110-6 Myr-1

• Lacc≈7 L > Lbol

• Inferred: Lacc<0.3 L

• TMC1:• Rotation<infall• Rc at 360 AU• Expanding t3

• Reaches 2000 AU in another (1–2)105 yr, ~twice current age and >> life time L1489’s diskHogerheijde (2001)

Open questionsOpen questions

• Transitional ‘large-disk’ stage?

• Redistribution of angular momentum, leading to smaller disk as seen around T Tauri stars?

• Do inward motions continue all the way to the star?



Keck/NIRSPEC CO gas and ice absorption lines at 4.7 µm (Boogert et al. 2002)

12CO ro-vibrational P,R lines

13CO ro-vibrational

lines +

12CO ice band

C18O ro-vibrational

lines ◊



• Average line profiles• 13CO < 12 km s-1

• 12CO wing extends to +100 km s-1

• Wings present in entire P,R branches

• Infall to within 0.1 AU from star

Boogert et al. (2002)



Infall model:Predicted average line profile

Flatter density profile: skimming flared disk surface

Infall model:Predicted average line profileFlatter density profile: skimming flared disk surfaceAdd 10% scattered star light

Boogert et al. (2002)



• Large disk, R~2000 AU• Inward motions from 2000 to <0.1 AU• Life time ~2104 yr ≈ 5% embedded phase• Disk ‘settling’ to rotationally supported size?• Supersonic motions

• Disk instability?

• Mass accretion rate >> observed if entire (inner) disk flows in• Inflow in surface layer only?

Summary and future workSummary and future work

• Cloud cores have velocity structure resembling rotation

• Turbulent origin likely

• Rotation not important for core’s dynamics

• Dense condensations decouple from magnetic breaking, spin up. R~4000–20,000 AU

• Disk forms at center, grows t1…3

• L1489 IRS: short-lived transitional stage, where large disk ‘settles’ to Keplerian structure

• Continued inflow puzzling. Contrary to expectation of viscous disk (subsonic accretion; disk spreading)

Summary and future workSummary and future work

• Find more objects like L1489 IRS: ~5% of YSOs

• Orientation of L1489 IRS may be advantageous

• Higher resolution observations of disk’s velocity structure: SMA, CARMA, ALMA

• Different chemical tracers: disk interior vs. surface

Infall and Rotation around Young Stars Formation and Evolution of Protoplanetary Disks Michiel R....

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