Precession of Isolated Neutron Stars. I. Effects of Imperfect Pinning

We consider the precession of isolated neutron stars in which superfluid isnot pinned to the stellar crust perfectly. In the case of perfect pinning,Shaham (1977) showed that there are no slowly oscillatory, long-lived modes.When the assumption of perfect pinning is relaxed, new modes are found that canbe long-lived, but are expected to be damped rather than oscillatory, unlessthe drag force on moving superfluid vortex lines has a substantial componentperpendicular to the direction of relative motion. The response of a neutronstar to external torques, such as the spindown torque, is also treated. We findthat when computing the response of a star to perturbations, assuming perfectcoupling of superfluid to normal matter from the start can miss some effects.Comment: 38 pages, uses aaspp4.sty, minor corrections; Final version to be published in Ap