Winds that Sail on Starlight Stan Owocki Bartol Research Institute University of Delaware...

Winds that Sail on Starlight

Stan Owocki

Bartol Research Institute

University of DelawareCollaborators:

– Asif Ud-Doula, U. Delaware

– Vikram Dwarkadas, U. Del.

– Ken Gayley, U. Iowa

– David Cohen, Swarthmore

– Steve Cranmer, CfA

– Joachim Puls, U. Munich

– Luc Dessart, Utrecht

– Mark Runacres, U. Brussels

2Winds that Sail on StarlightSTScI 11/07/01

Wind-Blown Bubbles in ISM

Some key scalings:

WR wind bubble NGC 2359 Superbubble in the

Large Magellanic Cloud

Henize 70: LMC SuperBubble


Pistol Nebula


Eta Carinae

STScI 11/07/01 Winds that Sail on Starlight 5

P-Cygni Line Profiles


Sailing vs. Radiative Driving

• Modern sails– asymmetric form + keel

– can tack against wind

– unstable to “keeling over”

• Line-driving ca. 2000– asymmetric velocity

gradient

– force not || flux• spindown & disk inhibition

• ablation & disk winds

– radiative braking

– small-scale instability

• CAK 1975– 1D spherically symmetric

– radially driven outflow

• Early sails – symmetric form

– sail mainly with wind


• Light transports energy (& information)

• But it also has momentum, p=E/c

• Usually neglected, because c is so high

• But becomes significant for very bright objects,

e.g. Lasers, Hot stars,

QSO/AGN’s

• Key question: how big is force vs. gravity??

Light’s Momentum


Free Electron Scattering

Thompson Cross Section

th

e-

Th= 2/3 barn= 0.66 x 10-24 cm2


• How big is electron scattering force vs. gravity??

• Expressed through a star’s Eddington parameter

~

gel

ggrav

eL4GMc

Eddington Parameter

• For sun, O ~ 2 x 10-5

• But for hot-stars with L~ 106 LO ; M=10-50 MO

r

L4 r2c

Th

e

GM2


Q~ ~ 1015 Hz * 10-8 s ~ 107

Q ~ Z Q ~ 10-4 107 ~ 103

Line Scattering: Bound Electron Resonance

lines~Q Th

glines~103g el

LLthin} iflines

~103

el 1

for high Quality Line Resonance,

cross section >> electron scattering


Optically Thick Line-Absorption in an Accelerating Stellar Wind

gthick~gthin

τ~

1ρ

dvdr

τ≡κρvth

dv/dr

LsobFor strong,

optically thick lines:


CAK model of steady-state wind

inertia gravity CAK line-accel.

Equation of motion: v ′ v ≈−GMr2 +

fQ Lr2

r2v ′ v ˙ M Q

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ α < 1

CAK ensemble ofthick & thin lines

˙ M ≈Lc2

Q−⎛

⎝⎜

⎞

⎠⎟

−Mass loss rate

˙ M v∞ ∝ L1

αWind-Momentum

Luminosity Law

≈0.6

v(r) ≈v∞(1−R∗/r)Velocity law

~vesc

* fix M to make line-accel. order gravity *.


Wolf-Rayet Winds• “Momentum #” =Mv/(L/c) > 1

• Requires multiple scattering

.

Need line spacing overlap v/v= > 1


Inward-propagating Abbott waves

±v ª ei(k r ° ! t)

°@v0

i!±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


Pulsation-induced wind variability

Velocity

Radius

radiative drivingmodulated by

brightness variations

Abbott-mode“kinks”

velocity “plateaus”

shockcompression


BW Vul: Observations vs. Model

C IV Model line


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


Line-Driven Instability

u=v/vth

for < Lsob:

g ~ u

Instability with growth rate

~ g/vth ~ v/Lsob ~100 v/R

=> e100 growth!


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


modelDessart

& Owocki

2002

WR Star Emission Profile Variability

WR 140Lepine &

Moffat 1999


WR+O Colliding wind

*WR Star

O Star

“Radiative Braking”

Pure Hydro

*WR Star

O Star

RadiationHydro

e.g., V444 Cygni


Gravity Darkeningincreasing stellar rotation

fast dense wind

slower windslower wind


Formation of Prolate Nebulae

-limit

Langer et al. 1999:Fast spherical wind into slow, dense equatorial flow

Dwarkadas et al. 2001Prolate fast wind into spherical medium

Gravity darkening


Wind Compressed Disk SimulationsVrot (km/s) = 200 250 300 350 400 450

radial forcesonly

WCD Inhibition by non-radial

line-forces


Vector Line-Force

r g line ~ d

*

∫rn I*

rn⋅[∇(

rn⋅

rv)]

dvn/dn

Net poleward line force from:

fasterpolarwind

slower equatorial wind

r

Max

[dv n

/dn]

(2) Pole-equator aymmetry in velocity gradient

r

Flux

(1) Stellar oblateness => poleward tilt in radiative flux

N


Wind rotation spindown from

azimuthal line-torque

g

(10 3 cm/s 2 )

[V

(nrf) - V

(wcd)]

*sin( )*r/Req

(km/s)

a. b.

-10

-30

-50

-70

-90

-0.1

-0.3

-0.5

-0.7

-0.9

azimuthalline-force

ang. mom.loss


I + I -I +

I +

I -

I -

Azimuthal Line-Torque

V+ <V_

g~V+ -V_ <


Line-Force in Keplerian Disk

r

dvr/dr z

dvz/dz


Accretion Disk Windsfrom BAL QSOs

blackhole

Xraysource

UV

failed windX-ray shield

UV line-drivenAccretion Disk Wind

radiatingaccretion

disk


Line-Driven Ablation

g lines ~ dv l

/dl

Net radiative Flux = 0, but glines ~ dvl/dl > 0 !


Be disk formation by RDOME(Radiatively Driven Orbital Mass Ejection)


MHD simulation of line-driven windZoom on densityDensityY- Velocity

-1000 vy (km/s) 1000


QuickTime™ and aBMP decompressor

are needed to see this picture.



295 G ; * = 1

Final state of ZPup isothermal models



1650 G ; * = 32 930 G ; * = 10



520 G ; * = 3.2



165 G ; * = 0.32



93 G ; * = 0.1


Summary• Lines efficient way for radiation to drive mass

– force depends of l.o.s. velocity gradient

– for non-spherical geometry, anisotropic opacity

– can get spindown, ablation, WCD inhibition, radiative braking, disk winds

• Line-driving very unstable for < LSob << R*

– leads to shocks, clumping, compressible turbulence

– may explain X-rays

• Current work– effect of NRP, B-field on wind

– application to BAL QSO/AGN disk winds

– formation of Be disks

– Super-Eddington Luminous Blue Variables

Winds that Sail on Starlight Stan Owocki Bartol Research Institute University of Delaware...

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