Nonradial neutron star oscillations

Abstract

The aim of this study is to introduce a formulation of the equations of motion for nonradial neutron star oscillations originally used in the context of terrestrial global seismology. The main advantage of this formulation is that it opens the way for faster and more accurate calculations of neutron star oscillation spectra. Using this formulation of the equations of motion, nonrelativistic and Cowling-approximated relativistic oscillation spectra for polytropic neutron stars with and without a crust are calculated. Existing results for the oscillation spectra of neutron stars are reproduced to show the validity of the equations of motion in the new formulation. New spectra for polytropic neutron star models with a crust are calculated. A comparison is made between the Cowling-approximated and exact nonrelativistic spectra of neutron star models with a crust. It is found that the new formulation of the equations of motion is applicable to neutron star seismology in both nonrelativistic and Cowling-approximated relativistic calculations. Further, it is shown that the nonrelativistic Cowling approximation has very little effect on crustal s-modes.