A NEW CLASS OF g-MODES IN NEUTRON STARS

Beca~se. a n~utron star is ~orn hot, its internal composition is close to chemical equilibrium. In the fluid core, thts tmphes_ that _the rat!o of the_ number densities of charged particles (protons and electrons) to neutrons, x ~.ncfnn, ts an mcreasmg function of the mass density. This composition gradient stably stratifies the m~tter glVlng ~ise to a Br~nt-Viiisiilii frequency N ~ (xgj2H) 112 ~ 500 s 1, where g is the gravitational acceleratto~, and H ts the denstty scale height. Consequently, a neutron star core provides a cavity that supports gra_vtty modes (g-modes). These g-modes are distinct from those previously identified with the thermal stratificatiOn of the surface layers and t~e chemical stratification of the crust. We compute the lowest-order, quadrupolar, g-modes for cold, Newtoman, neutron star models with M/M 0 = 0.581 and M/M 0 = 1.405 and show that t~e crustal and core g-modes have similar periods. We also discuss damping mechanisms and estimate ~ampmg ~at~s for the core g-modes. Particular attention is paid to damping due to the emission of gravitational radtatwn. Subject headings: stars: neutron stars: oscillations