Magnetically Confined Mountains on Accreting White Dwarfs

RESUMO

The hydromagnetic structure of magnetically confined mountains on accreting white dwarfs is computed, alongside the effects of accretion on the reduction of the star's magnetic field. The equilibrium structure of the mountain is obtained by numerically solving the Grad-Shafranov equation with a self-consistent scheme that enforces magnetic flux freezing. For characteristic system parameters, it is shown that magnetic field lines are significantly deformed and dragged equatorwards by mountains with masses $\sim10^{-3}M_\odot$ that have a characteristic height of $\sim10^5\,\mathrm{cm}$. A mathematical relation is obtained for the maximum mass that a white dwarf can confine magnetically given the star's magnetic field and temperature. It is found that the accretion buries the star's magnetic field by reducing it by up to $10\%$ of its pre-accretion value. The star's magnetic field remains dominantly dipolar, but with added multipolar components.