Crust-core coupling in rotating neutron stars

Motivated by their gravitational-wave driven instability, we investigate the influence of the crust on r-mode oscillations in a neutron star. Using a simplistic model of an elastic neutron star crust with constant shear modulus, we carry out an analytic calculation with the main objective of deriving an expression for the ``slippage’’ between the core and the crust. Our analytic estimates support previous numerical results, and provide useful insights into the details of the problem.