r-Mode Oscillations in Rotating Magnetic Neutron Stars

We show that r-mode oscillations distort the magnetic fields of neutron stars and that their occurrence is likely to be limited by this interaction. If the field is greater, similar1016(Omega/OmegaB) G, where Omega and OmegaB are the angular velocities of the star and at which mass shedding occurs, r-mode oscillations cannot occur. Much weaker fields will prevent gravitational radiation from exciting r-mode oscillations or will damp them on a relatively short timescale by extracting energy from the modes faster than gravitational-wave emission can pump energy into them. For example, a 1010 G poloidal magnetic field that threads the star's superconducting core is likely to prevent the l=2 mode from being excited unless Omega exceeds 0.35OmegaB. If Omega is larger than 0.35OmegaB initially, the l=2 mode may be excited but is likely to decay rapidly once Omega falls below 0.35OmegaB, which happens in less, similar15 days if the saturation amplitude is greater, similar0.1. The r-mode oscillations may play an important role in determining the structure of neutron star magnetic fields.