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

Possible. 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. Outline. Key properties of line-driven mass loss Wind variability

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

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  1. Possible 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

  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 IAUC 185

  3. Lsob Optically Thick Line-Absorption in an Accelerating Stellar Wind For strong, optically thick lines: IAUC 185

  4. 0 < a < 1 CAK ensemble of 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: IAUC 185

  5. @ v v = g r ad dg~ dv’ @ t i ( k r ° ! t ) ± v ª e @ g r ad 0 ° i! ± v = ± v ¥ U ik ± v @ v 0 w =k = ° U Abbott speed r 0 @ g g v v r ad r ad U = ª ª ª v @ v 0 v 0 v 0 Inward-propagating Abbott waves IAUC 185

  6. u=v/vth Line-Driven Instability Instability with growth rate W ~ g/vth ~ v/Lsob ~100 v/R =>e100 growth! for l < Lsob:dg/g ~ du IAUC 185

  7. Radius (R*) Radius (R*) Growth and phase reversal of periodic base perturbation IAUC 185

  8. Velocity Density Time snapshot of wind instability simulation CAK IAUC 185

  9. Cranmer 1996, PhD. Wave-leakage into outflowing wind IAUC 185

  10. Pulsation-Induced Wind Variations in BW Vul Steve Cranmer, Harvard-Smithsonian Stan Owocki, Bartol/U. of Del.

  11. BW Vul light curve IAUC 185

  12. Abbott-mode“kinks” Velocity velocity “plateaus” radiative driving modulated by brightness variations Radius shock compression log(Density) wind base perturbed by dr/r ~ 50 Wind variations from base perturbations in density and brightness IAUC 185

  13. Observations Model Radial velocity IAUC 185

  14. C IV Model line Observations vs. Model IAUC 185

  15. Rotational Modulation of Hot-Star Winds Radiation hydrodynamics simulation of CIRs in a hot-star wind • 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. HD64760 Monitored during IUE “Mega” Campaign IAUC 185

  16. Phase Bowing IAUC 185

  17. kinematic model with m=l=4 NRP Si IV observation HD 64760 (B0Ia) IAUC 185

  18. NIV in WR 6 m=4 dynamical model WR6 - Pulsational model IAUC 185

  19. So disk matter must be launched from star. The Puzzle of Be Disks • Be stars are too old to still have protostellar disk. • And most Be stars are not in close binary systems. • They thus lack outside mass source to fall into disk. How do Be stars do this?? IAUC 185

  20. Key Puzzle Pieces • Stellar Rotation • Be stars are generally rapid rotators • Vrot ~ 200-400 km/s < Vorbit ~ 500 km/s • 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 #’s1, 2, & 3 IAUC 185

  21. 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. DV=250 km/sec Vrot = 250 km/sec IAUC 185

  22. Flux Rotation Rotation + NRP Line-Profile Variations from Non-Radial Pulsation Line-Profile with: Wavelength (Vrot=1) NRP-distorted star (exaggerated) IAUC 185

  23. NRP Mode Beating l=3, m=2 l=2, m=1 l=4, m=2 IAUC 185

  24. 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?? IAUC 185

  25. CIR from Symmetric Bright Spot on Rapidly Rotating Be Star Vrot = 350 km/s Vorbit= 500 km/s Spot Brightness= 10 Spot Size = 10 o IAUC 185

  26. Symmetric Spot with Stagnated Driving IAUC 185

  27. Symmetric Prominence/Filament IAUC 185

  28. Time Evolution of m=4 Prograde Spot Model IAUC 185

  29. 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” IAUC 185

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