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. MacLow, J. Pittard, I. Stevens, P. Tuthill, R. Walder

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

July 10, HD64760 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. ¥These may stem from large-scale surface structure that induces spiral wind variation analogous to solar Corotating Interaction Regions. Radiation hydrodynamics simulation of CIRs in a hot-star wind Rotational Modulation of Hot-Star Winds

July 10, Hot-star winds intrinsically unstable at small-scales < L sob  v th /(dv/dr) Growth rate  g /v th  v  /L # e-folds  v/v th  In 1D simulations, leads to formation of multiple shocks In multi-D, expect supersonic “compressive turbulence” Line-Driven Instability in Wind Acceleration Region Velocity Density t=430 ksec

July 10, WR Wind Blobs Infer acceleration over extended scale:  R * ~ R O g rad ~  L * /4  r 2 c Requires radially increasing effective opacity  ~  /m Possible from desaturation of optically thick blobs Yields  ~  ~ r 2 g rad ~ constant! Lepine & Moffat 1999

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

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

July 10, Sudden Radiative Braking Diagnostic potential for line-driving opacity, e.g. in V444 Cyg Scaling analyses suggests broad importance in close to moderately separated WR+O systems Scaled Separation Scaled Momentum Ratio

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

July 10, Wind-Blown Bubbles in ISM Some key scalings: WR wind bubble NGC 2359 d pc =V 1000 ø _ Mø m ¥ 4º 3 Ω(Vø m ) 3 ø m =100 s _ M °6 V n 1 yrs M= 4º 3 Ωr 3 º0:1M Ø n 1 r 3 pc r = √ _ M °6 ø 5 n 1 ! 1=3

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

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

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

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

July 10, Radiative Shocks Hot Gas Cools by Line-Emission In 1D ideally develops characteristic layers µ∂ 4 N cool =7£10 17 V 100km=s cm 2

July 10, Reduction of X-ray emission Instantaneous wind acceleration 3x10 34 erg/s 8x10 32 erg/s Radiative wind acceleration 3D simulations of V444 Cygni (J. Pittard, Ph. Thesis, 1999):