Magnetars oscillations in the presence of a crust

We study axisymmetric perturbations of neutron star endowed with a strong magnetic field (magnetars), considering the coupled oscillations of the fluid core with the solid crust. We recover discrete oscillations based mainly in the crust and a continuum in the core. We also confirm the presence of "discrete Alfv\'en modes" in the gap between two contiguous continua (see Van Hooven& Levin (2011)) and, in addition, we can resolve some of them also inside the continua. Our results can explain both the lower and the higher observed quasi periodical oscillations (QPOs) in SGR 1806-20 and SGR 1900+14 and put constrains on the mass, radius and crust thickness of the two magnetars.