Links Between Pulsations & Line-Driven Mass Loss in Massive Stars

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

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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

July 30, 2001 IAUC 185 19

Phase Bowing

July 30, 2001 IAUC 185 20

HD 64760 (B0Ia)

Si IV observationkinematic model with

m=l=4 NRP

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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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July 30, 2001 IAUC 185 30

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”