Radiatively Driven Winds and Aspherical Mass Loss

Radiatively Driven Winds and Aspherical Mass Loss Stan Owocki U. of Delaware collaborators: Ken Gayley U. Iowa Nir Shaviv Hebrew U. Rich Townsend U. Delaware Asif ud-Doula NCSU

General Themes • Lines vs. Continuum driving • Oblate vs. Prolate mass loss • Smooth vs. Porous medium • Rotation vs. Magnetic field

if k gray e.g., compare electron scattering force vs. gravity s L Th g 2 k 4 r c L p m e e el G º = = g 4 GM c p GM grav 2 r • For sun, GO ~ 2 x 10-5 • But for hot-stars with L~ 106 LO ; M=10-50 MO . . . G<1 ~ Radiative force

Q~ n t ~ 1015 Hz * 10-8 s ~ 107 Q ~ Z Q ~ 10-4 107 ~ 103 ~ Q s ´ s lines Th g ~ 103 g ´ lines el } 3 if G ´ G >> ~ 10 1 lines el L L = thin Line Scattering: Bound Electron Resonance for high Quality Line Resonance, cross section >> electron scattering

Optically Thick Line-Absorption in an Accelerating Stellar Wind For strong, optically thick lines:

0 < a < 1 CAK ensembleof thick & thin lines Mass loss rate Velocity law Wind-Momentum Luminosity Law CAK model of steady-state wind Equation of motion: inertia gravity CAK line-force Solve for:

Wind Compressed Disk Model Bjorkman & Cassinelli 1993

Vrot (km/s) = 200 250 300 350 400 450 Vrot = 350 km/s with nonradial forces Wind Compressed Disk Simulations radial forces only

dvn/dn Net poleward line force from: (1) Stellar oblateness => poleward tilt in radiative flux (2) Pole-equator aymmetry in velocity gradient r N faster polar wind r Max[dvn/dn] Flux slower equatorial wind Vector Line-Force from Rotating Star

Gravity Darkening increasing stellar rotation

Vector line-force; With gravity dark.

highest at pole highest at pole w/ gravity darkening, if F(q)~geff(q) Effect of gravity darkening on line-driven mass flux

Rotational effect on flow speed *

Smith et al. 2002

Smith et al. 2003

O O But lines can’t explain eta Car mass loss

Super-Eddington Continuum-Driven Winds moderated by “porosity”

if k gray compare continuum force vs. gravity s L c g 2 k 4 r c L p m c c G º = = g 4 GM c p GM grav 2 r Continuum Eddington parameter constant in radius => no surface modulation

Convective Instability • Joss, Salpeter Ostriker 1973 • Classically expected in energy-generating core • e.g., CNO burning => e ~ T10-20 => dT/dr > dT/drad • But envelope also convective where G(r) -> 1 • e.g., z Pup: G*~1/2 => M(r) < M*/2 convective! • For high density interior => convection efficient • Lconv > Lrad- Lcrit => Grad (r) < 1: hydrostatic equilibrium • Near surface, convection inefficient => super-Eddington • but flow has M ~ L/a2 • implies wind energy Mvesc2 >> L • would“tire” radiation, stagnate outflow • suggests highly structured, chaotic surface . .

Photon tiring

Stagnation of photon-tired outflow

Shaviv 2001

Power-law porosity

Effective Opacity for "Blob"

“porosity length” Porous opacity

O Super-Eddington Wind Shaviv 98-02 Wind driven by continuum opacity in a porous medium when G* >1 At sonic point: “porosity-length ansatz”

Power-law porosity Now at sonic point:

Results for Power-law porosity model

highest at pole highest at pole w/ gravity darkening, if F(q)~geff(q) Effect of gravity darkening on porosity-moderated mass flux

Eta Carina

Summary Themes • Lines vs. Continuum driving • Oblate vs. Prolate mass loss • Smooth vs. Porous medium • Rotation vs. Magnetic field

e.g, for dipole field, q=3; h ~ 1/r4 Wind Magnetic Confinement Ratio of magnetic to kinetic energy density: for Homunclus, need B*~104G=> for present day eta Car wind, need B*~103G

MHD Simulation of Wind Channeling No Rotation Confinement parameter A. ud Doula PhD thesis 2002

Field aligned rotation A. ud-Doula, Phd. Thesis 2002

w=0.95 ; DVamp = a = 25 km/s = DVorb Disk from Prograde NRP

1.2 Density Azimuthal Velocity r/R* 1.0 0 5 10 5 10 time (days) 1.2 NRP On NRP Off Kepler Number Mass r/R* 0.98 1.0 1.0 Azimuthal Averages vs. r, t

Radiatively Driven Winds and Aspherical Mass Loss