Boundary-layer analysis of the core-crust interface in neutron stars

We investigate the influence of both rigid and elastic crusts on r-mode oscillations in a neutron star core fluid. This work is motivated by the possibility that the gravitational-wave driven instability of the inertial r-modes may become active in rapidly spinning neutron stars, eg. in low-mass X-ray binaries, and the fact that viscous Ekman layers at the core-crust interface provide an efficient damping mechanism for these oscillations. We review various approaches to the problem and carry out an analytic calculation of the effects due to the Ekman layer for rigid crusts, and a simplistic model of an elastic neutron star crust with constant shear modulus. Our analytic estimates support previous numerical results, and provide insights into the intricate effects present in the problem