Interacting Winds Theory Overview Stan Owocki Bartol Research

Interacting Winds: Theory Overview Stan Owocki Bartol Research Institute University of Delaware with thanks for web slides from: D. Folini, K. Gayley, S. Lepine, M. Mac. Low, J. Pittard, I. Stevens, P. Tuthill, R. Walder 1

Overview Hot-stars have massive, high-speed winds. These interact: u Internally F Large-scale, e. g. CIRs F Small-scale, e. g. , instability-generated turbulence u In high-mass binaries, e. g. WR-O u With environs: F Previous epoch outflow, e. g. slow RSG wind F ISM F SNe High-speed shocks, often unstable. July 10, 2000 2

Rotational Modulation of Hot-Star Winds HD 64760 Monitored during IUE “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. Radiation hydrodynamics simulation of CIRs in a hot-star wind ¥These may stem from large-scale surface structure that induces spiral wind variation analogous to solar Corotating Interaction Regions. July 10, 2000 3

Line-Driven Instability in Wind Acceleration Region n n Hot-star winds intrinsically unstable at small-scales l < Lsob ºvth/(dv/dr) Growth rate » g /vth » v /L # e-folds » v/vth » 100 Velocity Density In 1 D simulations, leads to formation of multiple shocks In multi-D, expect supersonic “compressive turbulence” July 10, 2000 4

WR Wind Blobs n n n Infer acceleration over extended scale: b. R* ~ 20 -50 RO Lepine & Moffat 1999 grad ~ k L*/4 p r 2 c Requires radially increasing effective opacity k ~ s/m Possible from desaturation of optically thick blobs Yields k ~ s ~ r 2 grad ~ constant! July 10, 2000 5

Colliding Wind Binaries n Close binaries: u X-ray attenuation u Radiative forces Inhibition F Braking F u n Interface instabilities Wide binaries: u Cometary or Spiral structure u Radio Emission u Dust formation July 10, 2000 6

Colliding Wind Momentum Balance Wind-wind balance Wind-radiation balance O-star radiation WR wind Symmetric or widely separated binaries Asymmetric (e. g. WR+O) close binaries July 10, 2000 7

Sudden Radiative Braking Diagnostic potential for line-driving opacity, e. g. in V 444 Cyg n Scaled Momentum Ratio n Scaling analyses suggests broad importance in close to moderately separated WR+O systems Scaled Separation July 10, 2000 8

Dust Spiral in WR 104 Tuthill et al. 1999 IR image from Keck How does dust form? July 10, 2000 9

Wind-Blown Bubbles in ISM Some key scalings: dpc = V 1000 ø 1000 M = 4º 3 3 Ωr º 0: 1 M Ø n 1 r pc 3 4º M_ øm ¥ Ω(V øm ) 3 3 s M_° 6 øm = 100 yrs 3 V 1000 n 1 WR wind bubble NGC 2359 √ r pc = M_° 6 ø 5 n 1 ! 1=3 July 10, 2000 10

Formation of Prolate Nebulae W-limit Langer et al. 1999: Fast spherical wind into slow, dense equatorial flow Gravity darkening Frank et al. 1998: Prolate fast wind into spherical medium July 10, 2000 11

Shock Interface Instabilities n g n Rayleigh-Taylor (heavy over light ) n Kelvin-Helmholtz (shear) n Cooling Overstabilty a Vishniac (gas-ram) & Thin-Shell (ram-ram) For summary, see J. Pittard Ph. D. thesis July 10, 2000 12

2 D Planar Simulation of Interaction Layer Walder & Folini 1998, 1999 Isothermal case: Thin-shell instability Radiative cooling case: Cooling overstability Density July 10, 2000 13

Questions Internal interactions u What induces large-scale DAC structure? NRP? B-fields? u What is lateral scale of instability structure? u What is origin of WR blobs? Instability? Pulsation? u What causes extended blob acceleration, b>>1 Wind-wind collisions u What reduces and softens X-ray emission? F Absorption? Conduction? Instability mixing? Braking? u Does Radiative Braking Occur? Even in clumped flows? u How does dust spiral form? Wind-environs u What determines nebula shape? e. g. , in h Car: u What causes the axisymmetry? Magnetic fields? Rotation? Radiation? F W-limit vs. gravity darkening July 10, 2000 14

Radiative Shocks n n Hot Gas Cools by Line-Emission In 1 D ideally develops characteristic layers N cool = 7 £ 1017 µ V 100 km=s ∂4 cm 2 July 10, 2000 15

Reduction of X-ray emission 3 D simulations of V 444 Cygni (J. Pittard, Ph. Thesis, 1999): Instantaneous wind acceleration 3 x 1034 erg/s Radiative wind acceleration 8 x 1032 erg/s July 10, 2000 16