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Dynamics of Stellar Winds in Massive Stars: Theory and Observations

Explore the intricate dynamics of stellar winds in massive stars, discuss emission lines, IR and radio excess, and the theory behind radiation-driven winds. Learn about P Cygni lines, formation processes, and challenges in determining mass loss rates. Delve into the impact of velocity, density, and radiation pressure in driving winds, and understand how rotational modulation influences wind behavior.

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Dynamics of Stellar Winds in Massive Stars: Theory and Observations

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  1. Stellar Winds of Massive Stars Lamers & Cassinelli (1999) P Cygni Lines Emission Lines IR and Radio Excess Emission Theory of Radiation Driven Winds

  2. [Steven Cranmer, CfA]

  3. Stellar Wind Outflows • Winds found in all luminous stars: Kudritzskihttps://www.ifa.hawaii.edu/users/kud/windsfromhotstars/hotwinds.html • Mass loss by radiative winds: momentum of radiation field captured by opaque lines in UV • loss rates: 10-6 solar masses/yr (⅓ Earth/yr) • terminal velocities: 103 km/sec • velocity law (β≈0.8):

  4. P Cygni Lines • formed by scattering in resonance lines • examples in IUE Atlas of O-type Spectra • terminal velocity, β determined but hard to get mass loss rate: need ionization model and unsaturated lines • need detailed structure of filling factor • FUSE: P V 1118, 1128 AngstromsFullerton et al. 2006, ApJ, 637, 1025

  5. Emission Lines • Hα; Paschen, Brackett lines in near IR • He II 1640, 4686 • numerous N, C lines in WR stars • formed by recombination (density2) in the base level of wind • strength depends on temperature and:

  6. IR and Radio Excess Emission • f-f (Bremsstrahlung) emission from outer parts of wind; excess flux at long wavelengths • kν ~ ν -2higher opacity at longer wavelength • if know T(r), v(r) then can determine mass loss rate from excess • effective size larger at longer wavelength (τ=1)

  7. CHARA image of wind of P Cyg in H-band Richardson et al. 2013, ApJ, 769, 118

  8. Theory of Radiation-Driven Winds • see handout from Kuditzki, Pauldrach & Puls1988, O Stars and WR Stars, NASA SP-497https://ntrs.nasa.gov/search.jsp?R=19890002286

  9. 2

  10. Velocity Density Radiation-Driven Winds from Hot-Stars • For hot, luminous stars the driving is generally thought to stem from radiation pressure acting through line scattering. • The Doppler shift of the line-profile within the expanding wind effectively “sweeps out” the star’s continuum momentum flux. • This makes the driving force a function of the wind velocity and acceleration, leading to strong instabilities that likely make such winds highly turbulent.

  11. Rotational Modulation of Winds These may stem from large-scale surface structure that induces spiral wind variation analogous to solar Corotating Interaction Regions. Monitoring campaigns of P-Cygni lines formed in hot-star winds also often show modulation at periods comparable to the stellar rotation period. HD64760 Monitored during IUE “Mega” Campaign Radiation hydrodynamics simulation of CIRs in a hot-star wind

  12. To really know a star ... get a spectrum • “If a picture is worth a thousand words, then a spectrum is worth a thousand pictures.”(Prof. Ed Jenkins, Princeton University)

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