links between pulsations & line-driven mass loss in massive stars
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Possible. Links Between Pulsations & Line-Driven Mass Loss in Massive Stars. Stan Owocki Bartol Research Institute University of Delaware. IAU Colloquium #185 Leuven, Belgium July 26-31, 2001. Outline. Key properties of line-driven mass loss Wind variability - PowerPoint PPT PresentationTRANSCRIPT
Links Between Pulsations & Line-Driven Mass Loss in Massive Stars
Stan Owocki
Bartol Research Institute
University of Delaware
IAU Colloquium #185
Leuven, Belgium
July 26-31, 2001
Possible
July 30, 2001 IAUC 185 2
Outline• Key properties of line-driven mass loss
• Wind variability– Discrete Absorption Components– Periodic Absorption Modulations
• Candidates for Pulsation Wind Connection– BW Vul– EZ CMa = WR 6
• Possible role of pulsation in initiating mass loss– WR winds
– Be disks
July 30, 2001 IAUC 185 3
Optically Thick Line-Absorption in an Accelerating Stellar Wind
gthick~gthin
τ~
1ρ
dvdr τ≡κρ
vth
dv/dr
Lsob
For strong,
optically thick lines:
July 30, 2001 IAUC 185 4
< 1CAK ensemble ofthick & thin lines
CAK model of steady-state wind
inertia gravity CAK line-force
Solve for:
˙ M ≈Lc2
QΓ1−Γ⎛
⎝⎜
⎞
⎠⎟
1
−1Mass loss rate
˙ M v∞ ∝ L1
αWind-Momentum
Luminosity Law
≈0.6
v(r) ≈v∞(1−R∗/r)Velocity law
~vesc
Equation of motion: v ′ v ≈−GM(1−Γ)
r2 +Q Lr2
r2v ′ v ˙ M Q
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ α
6 IAUC 185 July 30, 2001
Inward-propagating Abbott waves
±v ª ei(k r ° ! t)
°@v0i!±v =
@grad±v0
¥ U ik±v
w=k= ° U
U =@grad
@v0
ªgrad
v0 ªvv0
v0 ª v
ad@v@t
= gr
v
r
g~ v’
Abbott speed
July 30, 2001 IAUC 185 7
Line-Driven Instability
u=v/vth
for < Lsob:
g/g ~ u
Instability with growth rate
~ g/vth ~ v/Lsob ~100 v/R
=> e100 growth!
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Growth and phase reversal of periodic base perturbation
Radius (R*) Radius (R*)
July 30, 2001 IAUC 185 9
Time snapshot of wind instability simulation
0.0 0.5 1.0
0
500
1000
1500
-15
-14
-13
-12
-11
-10
Height (R*
)
Velocity
Density
CAK
July 30, 2001 IAUC 185 11
Wave-leakage into outflowing windCranmer 1996, PhD.
Pulsation-Induced Wind Variations
in BW Vul
Steve Cranmer, Harvard-Smithsonian
Stan Owocki, Bartol/U. of Del.
July 30, 2001 IAUC 185 13
BW Vul light curve
July 30, 2001 IAUC 185 14
Wind variations from base perturbations in density and brightness
log(Density)
Velocity
Radius
wind baseperturbed by
~ 50
radiative drivingmodulated by
brightness variations
Abbott-mode“kinks”
velocity “plateaus”
shockcompression
July 30, 2001 IAUC 185 15
Radial velocity
ModelObservations
July 30, 2001 IAUC 185 17
Observations vs. Model
C IV Model line
July 30, 2001 IAUC 185 18
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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Phase Bowing
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HD 64760 (B0Ia)
Si IV observationkinematic model with
m=l=4 NRP
July 30, 2001 IAUC 185 22
WR6 - Pulsational modelm=4 dynamical model NIV in WR 6
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The Puzzle of Be Disks
• And most Be stars are not in close binary systems.
• Be stars are too old to still have protostellar disk.
How do Be starsdo this??
• They thus lack outside mass source to fall into disk.
• So disk matter must be launched from star.
July 30, 2001 IAUC 185 25
Key Puzzle Pieces
• Stellar Wind– Driven by line-scattering of star’s radiation– Rotation can lead to Wind Compressed Disk (WCD) – But still lacks angular momentum for orbit
• Stellar Pulsation– Many Be stars show Non-Radial Pulsation (NRP) with m < l = 1 - 4
• Magnetic Spin-Up– Bdipole < 100 G => moment arm Ra < few R* ~ Rcorotation
• Here examine combination of #’s 1, 2, & 3
• Stellar Rotation– Be stars are generally rapid rotators
– Vrot ~ 200-400 km/s < Vorbit ~ 500 km/s
July 30, 2001 IAUC 185 27
Launching into Be star orbit• Requires speed of ~ 500 km/sec.
• Be star rotation is often > 250 km/sec at equator.
• Launching with rotation needs < 250 km/sec
• Requires < a quarter of the energy!
• Localized surface ejection self selects orbiting material.
Vrot = 250 km/sec
V=250 km/sec
July 30, 2001 IAUC 185 29
Line-Profile Variations from
Non-Radial Pulsation
Wavelength (Vrot=1)
Flux
Rotation
Rotation+
NRP
NRP-distorted star(exaggerated)
Line-Profile with:
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NRP Mode Beating
l=3, m=2
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l=2, m=1
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l=4, m=2
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NonRadial Radiative Driving
• Light has momentum.
• Pushes on gas that scatters it.
• Drives outflowing “stellar wind”.
• Pulsations distort surface and brightness.
• Could this drive local gas ejections into orbit??
July 30, 2001 IAUC 185 32
CIR from Symmetric Bright Spot on Rapidly Rotating Be Star
Vrot = 350 km/sVorbit= 500 km/s
Spot Brightness= 10Spot Size = 10 o
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Symmetric Spot with Stagnated Driving
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Symmetric Prominence/Filament
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Time Evolution of m=4 Prograde Spot Model
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Summary
• High-freq. p-modes feed line-driven instability
• g-modes can “leak” into wind
• Radial pulsational light curve modulates mass loss– distinctive Abbott kinks with velocity plateaus
• NRP light variations can lead to CIRs
• in Be stars NRP resonances might induce “orbital mass ejection”