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O. M. Umurhan (Stanford U., Center for Turbulence Research), L Tao (Columbia U.)
Recently Spiegel & Tao studied the linear stability of photo-acoustic modes of a plane-parallel atmosphere supported by radiative forces at a moderate fraction of the Eddington luminosity. Their numerical boundary value work showed that the compressional modes are most unstable for horizontal wave numbers of order unity. This is in contrast to the photon bubble instability described and analyzed by Arons et al (1990, 1997) to model the structures observed in numerical simulations of magnetized pulsars. The photon bubble instability occurs in magnetized, radiation dominated atmospheres at high horizontal wave numbers. Asymptotic solutions are generated to demonstrate the qualitative similarities between the small wave number photoacoustic instability and Rayleigh's thermoacoustic instability. We conclude by a discussion of the difference between the photon bubble process and the photoacoustic instability.