R-modes in neutron stars with crusts: Turbulent saturation, spin-down, andcrust melting

Rossby waves (r-modes) have been suggested as a means to regulate the spin periods of young or accreting neutron stars and also to produce observable gravitational wave radiation. R-modes involve primarily transverse, incompr essive motions of the star's fluid core. However, neutron stars gain crusts early in their lives; therefore, r-modes also imply shear in the fluid ben eath the crust. We examine the criterion for this shear layer to become tur bulent and derive the rate of dissipation in the turbulent regime. Unlike d issipation from a viscous boundary layer, turbulent energy loss is nonlinea r in mode energy and can therefore cause the mode to saturate at amplitudes typically much less than unity. This energy loss also reappears as heat be low the crust. We study the possibility of crust melting as well as its pot ential implications for the spin evolution of low-mass X-ray binaries. Last ly, we identify some universal features of the spin evolution that may have observational consequences.