outflows from ysos and angular momentum transfer national astronomical observatory (naoj) kohji...
DESCRIPTION
Angular Momentum Transfer Magnetic Braking Alfven Speed Ambient density Column density Free-fall time in ambient matter >1: For super- critical clouds Longer than dynamical time B-Fields do not play a role in angular momentum transfer in a contracting cloud?TRANSCRIPT
Outflows from YSOs and Angular Momentum Transfer
National Astronomical Observatory (NAOJ)
Kohji Tomisaka
Angular Momentum
• Fragmentation (binary formation) is much affected by the amount of angular momentum in rotation supported disk cr.
• Angular Momentum Problem: j* << j cl Specific angular momentum of a new-born star:
is much smaller than that of parent cloud:j RR
P*
* FH IKFHG IKJ6 102 10
162
daycm s
-12 -1
j Rcl -1 -1
2 -1
pc kms pccm s
FHG IKJ FHG IKJ5 100 1 4
212
.
Angular Momentum Transfer
• Magnetic Braking
tV
GB
GBa A
a
( ) /
2
2 40
1 2
a
vA
Alfven Speed
Ambient density
Column density Free-fall time in ambient matter
>1: For super-critical clouds
Longer than dynamical time
•B-Fields do not play a role in angular momentum transfer in a contracting cloud?
Angular Momentum Redistribution in Dynamical
Collapse• In outflows driven by magnetic fields:
– The angular momentum is transferred effectively from the disk to the outflow.
– If 10 % of inflowing mass is outflowed with having 99.9% of angular momentum, j* would be reduced to 10-3 jcl.
Outflow
Disk
B-FieldsOutflow
MassInflow star Outflow
Ang.Mom.
Shu’s Inside-out SolutionLarson-Penston SolutionOutflow
What we have done.• Dynamical contraction of slowly rotating
magnetized clouds is studied by ideal MHD numerical simulations with cylindrical symmetry.
• Evolution is as follows: Run-away Collapse Increase in Central Density Formation of Adiabatic Core Accretion Phase
Numerical Method• Ideal MHD + Self-Gravity +
Cylindrical Symmetry• Collapse: nonhomologous• Large Dynamic Range is att
ained by Nested Grid Method.– Coarse Grids: Global Structur
e – Fine Grids: Small-Scale Struc
ture Near the Core
L0 L231
1/21/4
Initial Condition
• Cylindrical Isothermal Clouds– Magnetohydrostatic ba
lance in r-direction– uniform in z-direction
• B-FieldsB B Bz r , 0
• Slowly rotating (~ rigid-body rotation)
• Added perturbation with of the gravitationally most unstable mode MGR.
M
GR
parameters
1 50, (L2)
t=0 0.6Myr 1Myr
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Run-away Collapse Phase
Accretion Phase
• High-density gas becomes adiabatic.– The central core becomes optically thick for ther
mal radiation from dusts.– Critical density =
• An adiabatic core is formed.• To simulate, a double polytrope is applied
– isothermal– adaiabatic
1ncrit
-3cm 1010
p cs 2
p K
= 7 / 5 = 5 / 3
n n crit
n n crit
Accretion Phase (II)
• Collapse time-scale in the adiabatic core becomes much longer than the infall time.
• Inflowing gas accretes on to the nearly static core, which grows to a star.
• Outflow emerges in this phase.
Outflow
Core + Contracting Disk
Pseudo-Disk
Accretion Phase B0,
Adiabatic (the first) Core
A Ring Supported by Centrifugal Force
Run-away Collapse Stage Accretion Stage
Accretion Phase 0 , B=0
z
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Accretion Phase B0, 0
Run-away Collapse Stage 1000yr
L10
300A
U
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Why Does the Outflow Begin in the Accretion Stage?
Run- awayC ollapse
Accretionstage
Rotation Speed v vr
v v r
T oroidal B - F ield B B pol B B pol
Rotation Angle
c cG/
. .
20 2 0 4
d i
muchAngle betweenB- F ields and adisk
60 – 70 deg 10 – 30 deg
B0, 0Accretion Phase
Blandford & Peyne 82
Mass Accretion RateMagneto-Centrifugal Wind
Angular Momentum Distribution
L rv dV( )
z1
1
M dV( )
z1
1
j M LM
( ) ( )( )
1
1
(1) Mass measured from the center
(2) Angular momentum in
(3) Specific Angular momentum distribution
M( ) 1
Angular Momentum Problem
Core Formation
7000 yr afterCore Formation
Mass
Specific Angular Momentum
Initial
High-density region is formed by gases with small j.
Run-away Collapse
Magnetic torque brings the angular momentum from the disk to the outflow.
Outflow brings the angular momentum.
Accretion Stage
Angular Momentum Problem
Magnetic Torque, Angular Momentum Inflow/Outflow Rate
Mass
Initial
Torque
Inflow Outflow
Accretion Phase Inflow
Torque
Core Formation
Inflow
Torque
• In weakly ionized plasma, neutral molecules have only indirect coupling with the B-fields through ionized ions.
• Neutral-ion collision time• When , ambipolar diffusion is import
ant.• Assuming (on core formatio
n), rotation period of centrifugal radius:
rot yrms
FHIKFH IKFH IK
2 4000 1 0 1 190
33
3
1
3
p GMc
p MM
c
s
s
. .
Ambipolar Diffusion?
niiK n
200yr
5 81 2/
j GMc
GMcs s
( . . )0 1 0 25
ni rot
ni dyn
Edge of Hole madeby Molecular Outflow
Molecular Outflow Optical Jets
L1551 IRS5 Optical Jets
105 AU
12 1 0CO J
Optical Jets
• Flow velocity: faster than molecular outflow.• The width is much smaller.
• These indicate ‘Optical jets are made and ejected from compact objects.’
• The first outflow is ejected just outside the adiabatic (first) core.
Jets and Outflows
• Optical jets are formed just outside the second core?
Temperature-Density RelationJets and Outflows
Temperature-Density Relation
adiab
atic
H 2 Disso
c.
isothermal
1st Core
2nd CoreLo
g T
Log
Outflows
Jets?Log 5 10 15
1
2
3
4
Tohline 1982
10 5
2 10 5
0 002.
zOutflow
Jetsz
zJets and Outflows
s=104H2cm-3
=1,
L8
L16
10AU
10Rc=1014.6H2cm-3
c=1019H2cm-3
c=1021.3.H2cm-3
H 2 D
issoc
.
10R
2nd RunawayCollapse
X256
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Summary
• In dynamically collapsing clouds, the outflow emerges just after the core formation (yr).
• In the accretion phase, the centrifugal wind mechanism & magnetic pressure force work efficiently.
• In 7000 yr ( ), the outflow reaches 2000 AU. Maximum speed reaches
M M* . 0 2
v cc
ss
max-1
-1 km s m s
FH IK7 1 3190
. .
Summary(2)
• In the process, the angular momentum is transferred from the disk to the outflow and the outflow brings the excess j.
• This solves the angular momentum problem of new-born stars.
• The 2nd outflow outside the 2nd (atomic) core explains optical jets.
Runaway Collapse Accretion-associated Collapse
Den
sity
incr
ease
s inf
inite
lyInside-out CollapseHydrostatic Core
Larson 1969, Penston 1969, Hunter 1977,Whitworth & Summers 1985
Shu 1977
Dynamical Collapse
Parameters
• Angular Rotation Speed
• Magnetic to thermal pressure ratio
014
1 2
09 10100 5
FHG IKJ F
HGIKJ rad s
H cm-1
2-3
ns
/
( / ) / , .B p02 4 1 0 1th
vr
FH IKFHG IKJ2 79 10
014. km s
rad s 1pc-1
-1cl
Nest (Self-Similar) Structure
L5
L12
z
vzBz
z
2 1287
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Run-away Collapse Phase
Along z-axis
Run-away Collapse
• Evolution characterized as self-similar 10AU
0 1. pc
Magnetocentrifugal Wind Model:Blandford & Peyne 1982
• Consider a particle rotating with rotation speed = Kepler velocity and assume is conserved moving along the B-fields.
• Along field lines withdeg the particle is accelerated. For deg decelerated.
Effective potential for a particle rotating with
Momentum Flux (Observation)• Low-Mass YSOs (Bontemps et al.1996)
Class0Class1
F L cbolCO /
Luminosity
Mom
entu
m
Angular Momentum
L rv dV( )
z1
1
M dV( )
z1
1
j M LM
( ) ( )( )
1
1
(1) Mass measured from the center
(2) Angular momentum in
(3) Specific Angular momentum distribution
j M( )
M( ) 1
Angular Momentum Problem
Effective Outflow Speed
V
dMVdt
dMdt
eff
Outflow Driving Mechanism
• Rotating Disk + Twisted Magnetic Fields– Centrifugal Wind +
• Pudritz & Norman 1983;• Uchida & Shibata 1985;• Shu et al.1994; • Ouyed & Pudritz 1997;• Kudoh & Shibata 1997
• Contraction vs Outflow?• When outflow begins?
• Condition?
Outflow
Disk
B-FieldsOutflow
Inflow
Accretion/Outflow Rate
• Inflow Rate is Much Larger than Shu’s Rate (1977).
• LP Solution: • Outflow/Inflow Mass
Ratio is Large ~ 50 %.• Source Point of Outflo
w Moves Outward.
m v ndS z
0 975 3. /c Gs
29 3c Gs /
10 5 M -1yr
mShu
6000yr2000yr 4000yr
1
2
3
4
Momentum Driving Rate
• Molecular Outflows (Class 0&1 Objects) show Momentum Outflow Rate (Bontemps et al.1996)
3 10 5 106 4 yr km s-1 -1M
dmvdt
v dSzz z 2
Upper / Lower
Boundaries
1 10 5 M yr km s-1 -1
6000yr2000yr 4000yr
2 10 5 M yr km s-1 -1
Weak Magnetic Fields (=0.1,)
0 yr 2000 yr 4000 yr ビデオ クリップ
B0, 0Accretion Phase
Effect of B-Field Strength
• In small model, toroidal B-fields become dominant against the poloidal ones.
• Poloidal B-fields are winding. • Small and slow rotation lead less effecti
ve acceleration.
B0, 0Accretion Phase
Angular Momentum Problem
• Typical specific angular momentum of T Tauri stars
• Angular momentum of typical molecular cores
• Centrifugal Radius
j RR
P*
* FH IKFHG IKJ6 102 10
162
daycm s
-12 -1
j Rcl -1 -1
2 -1
pc kms pccm s
FHG IKJ FHG IKJ5 100 1 4
212
.
R jGM
j MMc
FH IKFHIK
2 1
0 06. pc5 10 cm s21 2 -1
2
R Rc *
j jcl *
Angular Momentum Problem
Molecular Outflow H CO+13
1400AU = 10"
Saito, Kawabe, Kitamura&Sunada 1996 L1551 IRS5Optical Jets
105 AU
12 1 0CO J
Snell, Loren, &Plambeck 1980