r‐Modes in the Ocean of a Magnetic Neutron Star

We study the dynamics of r-modes in the ocean of a magnetic neutron star. Wemodeled the star's ocean with a spherical rotating thin shell and assumed thatthe magnetic field symmetry axis is not aligned to the shell's spin axis. Inthe magnetohydrodynamic approximation, we calculate the frequency of $\ell=m$r-modes in the shell of an incompressible fluid. Different r-modes with $\ell$and $\ell\pm2$ are coupled by the {\it inclined} magnetic field. Kinematicalsecular effects for the motion of a fluid element in the shell undergoing$\ell=m=2$ r-mode are studied. The magnetic corrected drift velocity of a givenfluid element undergoing the $\ell=m$ r-mode oscillations is obtained. Themagnetic field increases the magnitude of the fluid drift produced by ther-mode drift velocity, the high-$\ell$ modes in the ocean fluid will dampfaster than the low-$\ell$ ones.Comment: 24 pages, 5 figures, to appear in ApJ, v574 n2 August 1, 2002 issu