Interacting Winds: Theory Overview
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Transcript of Interacting Winds: Theory Overview
Interacting Winds: Theory OverviewStan Owocki
Bartol Research InstituteUniversity of Delaware
with thanks for web slides from:D. Folini, K. Gayley, S. Lepine, M. MacLow, J. Pittard, I. Stevens, P. Tuthill, R. Walder
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OverviewHot-stars have massive, high-speed winds.
These interact: Internally
Large-scale, e.g. CIRs Small-scale, e.g., instability-generated turbulence
In high-mass binaries, e.g. WR-O With environs:
Previous epoch outflow, e.g. slow RSG wind ISM SNe
High-speed shocks, often unstable.
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HD64760 Monitored duringIUE “Mega” Campaign
Monitoring campaigns of P-Cygni lines formed in hot-star winds also often show modulation at periods comparable to the stellar rotation period.
These may stem from large-scale surface structure that induces spiral wind variation analogous to solar Corotating Interaction Regions.
Radiation hydrodynamicssimulation of CIRs in a hot-star wind
Rotational Modulation of Hot-Star Winds
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Hot-star winds intrinsically unstable at small-scales < Lsob vth/(dv/dr)
Growth rate g /vth v/L # e-folds v/vth
In 1D simulations, leads to formation of multiple shocks
In multi-D, expect supersonic “compressive turbulence”
Line-Driven Instability in Wind Acceleration Region
0.0 0.5 1.0
0
500
1000
1500
-15
-14
-13
-12
-11
-10
Height (R*
)
Velocity
Density
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WR Wind Blobs
Infer acceleration over extended scale: R* ~ 20-50 RO
grad ~ L*/4r2c
Requires radially increasing effective opacity ~ /m
Possible from desaturation of optically thick blobs
Yields ~ ~ r2 grad ~ constant!
Lepine & Moffat 1999
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Colliding Wind Binaries
Close binaries: X-ray attenuation Radiative forces
Inhibition Braking
Interface instabilities
Wide binaries: Cometary or Spiral
structure Radio Emission Dust formation
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Colliding Wind Momentum Balance
Wind-wind balance Wind-radiation balance
WR wind
O-star radiation
Symmetric or widely separated binaries
Asymmetric (e.g.WR+O) close binaries
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Sudden Radiative Braking Diagnostic potential for
line-driving opacity, e.g. in V444 Cyg
Scaling analyses suggests broad importance in close to moderately separated WR+O systems
Scaled Separation
Sca
led
Mom
entu
m R
atio
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Dust Spiral in WR 104
Tuthill et al. 1999
IR image from Keck
How does dust form?
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Wind-Blown Bubbles in ISM
Some key scalings:
WR wind bubble NGC 2359
dpc =V1000ø1000
_Møm ¥4º3Ω(Vøm)3
øm =100
s_M °6
V 31000n1
yrs
M =4º3Ωr3 º 0:1 MØ n1 r3pc
rpc =
√_M ° 6 ø5n1
! 1=3
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Formation of Prolate Nebulae
Frank et al. 1998:Prolate fast wind into spherical medium
-limit
Langer et al. 1999:Fast spherical wind into slow, dense equatorial flow
Gravity darkening
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Rayleigh-Taylor (heavy over light )
Vishniac & Thin-Shell (gas-ram) (ram-ram)
Shock Interface Instabilities Kelvin-Helmholtz (shear)
Cooling Overstabilty
g a
For summary, see J. Pittard Ph.D. thesis
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2D Planar Simulation of Interaction Layer
Walder & Folini
1998,1999
Density
Isothermal case:
Thin-shell instabilityRadiative cooling case:
Cooling overstability
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QuestionsInternal interactions
What induces large-scale DAC structure? NRP? B-fields?
What is lateral scale of instability structure?
What is origin of WR blobs? Instability? Pulsation?
What causes extended blob acceleration, >>1
Wind-wind collisions What reduces and softens X-ray emission?
Absorption? Conduction? Instability mixing? Braking?
Does Radiative Braking Occur? Even in clumped flows?
How does dust spiral form?
Wind-environs What determines nebula shape? e.g., in Car:
What causes the axisymmetry? Magnetic fields? Rotation? Radiation? -limit vs. gravity darkening
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Radiative Shocks Hot Gas Cools by
Line-Emission
In 1D ideally develops characteristic layers
µ ∂4
Ncool=7 £1017V
100km=scm2
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Reduction of X-ray emission
Instantaneous wind acceleration
3x1034 erg/s 8x1032 erg/s
Radiative wind acceleration
3D simulations of V444 Cygni (J. Pittard, Ph. Thesis, 1999):