Stellar Winds of Massive Stars Lamers Cassinelli 1999

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

[Steven Cranmer, Cf. A] 2

Stellar Wind Outflows • Winds found in all luminous stars: Kudritzski https: //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): 3

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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 Angstroms Fullerton et al. 2006, Ap. J, 637, 1025 5

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Emission Lines Hα; Paschen, Brackett lines in near IR He II 1640, 4686 numerous N, C lines in WR stars formed by recombination (density 2) in the base level of wind • strength depends on temperature and: • • 8

IR and Radio Excess Emission • f-f (Bremsstrahlung) emission from outer parts of wind; excess flux at long wavelengths • kν ~ ν -2 higher 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) 9

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CHARA image of wind of P Cyg in H-band Richardson et al. 2013, Ap. J, 769, 118 11

Theory of Radiation-Driven Winds • see handout from Kuditzki, Pauldrach & Puls 1988, O Stars and WR Stars, NASA SP-497 https: //ntrs. nasa. gov/search. jsp? R=19890002286 12

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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. Velocity Density

Rotational Modulation of Winds Monitoring campaigns of P-Cygni lines formed in hot-star winds also often show modulation at periods comparable to the stellar rotation period. HD 64760 Monitored during IUE “Mega” Campaign 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

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) 21