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A. Spitkovsky (UC Berkeley), G. Ushomirsky (MIT Lincoln Lab), Y. Levin (CITA)
We present the results of ``shallow water" and multilayer "primitive equations" simulations of ignition and propagation of thermonuclear burning in the atmosphere of a rapidly rotating neutron star during a type I X-ray burst. Simulations are performed on a sphere, allowing us to study the effects of the latitude-dependent Coriolis force. We find that the burning propagates due to coherent cross-front circulation in geostrophically balanced burning fronts (Spitkovsky, Levin, Ushomirsky 2002), and that burning vorticies tend to drift against the direction of rotation of the star and towards the equator, eventually igniting the equatorial belt. We study the excitation of equatorially trapped Rossby and solitary waves and demonstrate vortex formation in the shearing zonal flow. All of these modes are retrograde in the frame of the star and can contribute to the burst oscillation phenomenon. We discuss the properties of the atmosphere needed in order to match the frequency of oscillations with observations, and address the dependence of simulated oscillations on the location of ignition.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.