Viscous dissipative effects in white dwarfs and neutron stars

Abstract

When a differentially rotating magnetic star undergoes ``turn-over'', i.e., its magnetic symmetry axis is inclining at a gradually increasing angle with respect to its invariant angular momentum axis up to the perpendicular position (situation known as ``perpendicular rotator''), the poloidal magnetic field causes interchange of angular momentum via hydromagnetic Alfven waves propagating along the poloidal magnetic field lines and, accordingly, the resulting perpendicular rotator obtains uniform rotation. This dissipative mechanism is represented by the so-called ``turn-over viscosity''. For several white dwarf and neutron star models, we compute the energy dissipation due to the turn-over viscosity; we also compare this effect with the corresponding dissipative effects induced by the electron, ion, and turbulent viscosity.