A Numerical Study of Normal Modes of Rotating Neutron Star Models by the Cowling Approximation

A numerical method of mode analysis of rapidly rotating relativistic stellar models by the Cowling approximation is applied to rotating neutron stars with realistic equations of state. For selected equations of state, eigenvalues and eigenfunctions of f-modes are numerically solved for stellar models from non-rotating to maximally rotating states. Neutral points of the lower order f-modes are determined as a function of the stellar rotational frequency. As in the polytropic case, we find that the bar mode can have neutral points for models with relatively strong gravity. The rotational frequency at the neutral point increases as the gravitational mass of the model becomes larger. As astrophysical applications of our analysis, we discuss the time scales of gravitational radiation induced instability and the possibility of the resonant excitation of f-modes during inspiraling motion of compact binary systems.

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