Cranmer, S. R. 2007, "Propagating Waves in Hot-Star Winds: Leakage of Long-Period Pulsations," IAU Symposium 250: Massive Stars as Cosmic Engines,, Kauai, Hawaii, December 2007 (poster). [see also the Powerpoint poster (1.3 MB), scaled down to fit on a Letter-sized sheet]
Massive stars have strong stellar winds that exhibit variability on time scales ranging from hours to years. Many classes of these stars are also seen, via photometric or line-profile variability, to pulsate radially or nonradially. It has been suspected for some time that these oscillations can induce periodic modulations in the surrounding stellar wind and produce observational signatures in line profiles or clumping effects in other diagnostics. The goal of this work is to investigate the detailed response of a line-driven wind to a given photospheric pulsation mode and amplitude. We ignore the short-wavelength radiative instability and utilize the Sobolev approximation, but we use a complete form of the momentum equation with finite-disk irradiation and finite gas pressure effects. For large-scale perturbations appropriate for the Sobolev approximation, though, the standard WKB theory of stable "Abbott waves" is found to be inapplicable. The long periods corresponding to stellar pulsation modes (hours to days) excite wavelengths in the stellar wind that are large compared with the macroscopic scale heights. Thus, both non-WKB analytic techniques and numerical simulations are employed to study the evolution of fluctuations in the accelerating stellar wind. This progress report describes models computed with one-dimensional (radial) isothermal motions only. However, even this simple case produces a quite surprising complexity in the phases and amplitudes of velocity and density, as well as in the distribution of outward and inward propagating waves throughout the wind.
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