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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 – 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 July 30, 2001 IAUC 185 2 Optically Thick Line-Absorption in an Accelerating Stellar Wind For strong, optically thick lines: July 30, 2001 gthin 1 dv gthick ~ ~ dr IAUC 185 Lsob v th dv / dr 3 CAK model of steady-state wind Equation of motion: a 2 GM(1 ) Q L r vv vv 2 Ý 2 r r MQ inertia gravity 0<a<1 CAK ensemble of thick & thin lines CAK line-force Solve for: Mass loss rate L Q Ý M 2 c 1 1 a 1 Wind-Momentum Luminosity Law July 30, 2001 Velocity law v(r) v (1 R / r) ~ vesc 1 Ýv La M IAUC 185 a 0.6 4 Inward-propagating Abbott waves @v = gr ad @t ° i! ±v = ±v ª ei (k r ° ! t) w=k = ° U @gr ad 0 ±v 0 @v ¥ U ik ±v dg~ dv’ v Abbott speed @gr ad U= @v0 gr ad vv 0 ª ª ª v 0 0 v v July 30, 2001 r IAUC 185 6 Line-Driven Instability u=v/vth for l < Lsob: dg/g ~ du July 30, 2001 Instability with growth rate W ~ g/vth ~ v/Lsob ~100 v/R => e100 growth! IAUC 185 7 Growth and phase reversal of periodic base perturbation Radius (R*) July 30, 2001 Radius (R*) IAUC 185 8 Time snapshot of wind instability simulation CAK 1500 -10 -11 1000 Velocity -12 Density -13 500 -14 0 -15 0.0 0.5 1.0 Height (R * ) July 30, 2001 IAUC 185 9 Wave-leakage into outflowing wind Cranmer 1996, PhD. July 30, 2001 IAUC 185 11 Pulsation-Induced Wind Variations in BW Vul Steve Cranmer, Harvard-Smithsonian Stan Owocki, Bartol/U. of Del. BW Vul light curve July 30, 2001 IAUC 185 13 Wind variations from base perturbations in density and brightness Abbott-mode“kinks” Velocity velocity “plateaus” radiative driving modulated by brightness variations log(Density) shock compression Radius wind base perturbed by d/ ~ 50 July 30, 2001 IAUC 185 14 Radial velocity Observations July 30, 2001 Model IAUC 185 15 Observations vs. Model C IV July 30, 2001 Model line IAUC 185 17 Rotational Modulation of Hot-Star Winds HD64760 Monitored during IUE “Mega” Campaign 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. Monitoring campaigns of PCygni lines formed in hot-star winds also often show modulation at periods comparable to the stellar rotation period. July 30, 2001 IAUC 185 18 Phase Bowing July 30, 2001 IAUC 185 19 HD 64760 (B0Ia) kinematic model with Si IV observation m=l=4 NRP July 30, 2001 IAUC 185 20 WR6 - Pulsational model NIV in WR 6 m=4 dynamical model July 30, 2001 IAUC 185 22 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?? • So disk matter must be launched from star. July 30, 2001 IAUC 185 24 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 #’s 1, 2, & 3 July 30, 2001 IAUC 185 25 Launching into Be star orbit • Requires speed of ~ 500 km/sec. DV=250 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! Vrot = 250 km/sec • Localized surface ejection self selects orbiting material. July 30, 2001 IAUC 185 27 Line-Profile Variations from Non-Radial Pulsation Line-Profile with: Rotation Flux QuickTime™ and a Animation decompressor are needed to see this picture. Wavelength (Vrot=1) NRP-distorted star (exaggerated) July 30, 2001 Rotation + NRP IAUC 185 29 NRP Mode Beating QuickTime™ and a Animation decompressor are needed to see this picture. QuickTime™ and a Animation decompressor are needed to see this picture. l=3, m=2 l=2, m=1 l=4, m=2 QuickTime™ and a Animation decompressor are needed to see this picture. July 30, 2001 IAUC 185 30 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?? July 30, 2001 IAUC 185 31 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 July 30, 2001 QuickTime™ and a Graphics decompressor are needed to see this picture. IAUC 185 32 Symmetric Spot with Stagnated Driving QuickTime™ and a Graphics decompressor are needed to see this picture. July 30, 2001 IAUC 185 33 Symmetric Prominence/Filament QuickTime™ and a Graphics decompressor are needed to see this picture. July 30, 2001 IAUC 185 34 Time Evolution of m=4 Prograde Spot Model QuickTime™ and a Graphics decompressor are needed to see this picture. July 30, 2001 IAUC 185 36 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” July 30, 2001 IAUC 185 37