SURFACE VIBRATIONS OF STRATIFIED NEUTRON STAR IN THE NEWTONIAN LIMIT OF GRAVITY

Abstract

From theoretical analysis of the radial distribution of bulk density in the neutron star interior it follows that a neutron star is a strongly stratified compact stellar object with a rather complicated layering structure: the density of outer layers (crust, neutron-rich nuclei, electrons) is much less than the density of the inner region of the stiff core (dense matter of superfluid neutrons, superconducting protons). Simplifying this picture we study the surface vibrations of a nonrotating neutron star in the model of a rigid-like inert core covered by the dynamical liquid-like layer; the effects of gravity are described in the Newtonian limit. The eigenfrequencies of surface pulsations are derived in the analytic form as a function of multipole degree of spheroidal configurations, densities and radii of the core and outer layer. The conclusions of the liquid layer model are compared with those for the Kelvin model of a heavy liquid drop to find out the difference in the eigenfrequencies of spheroidal vibrations corresponding to neutron stars with approximately uniform distribution of density and stars with stratified mass distribution.