The spectrum and dipole and quadrupole moments of hydrogen-like and helium-like ions in superstrong fields

The properties of hydrogen-like and helium-like systems in superstrong magnetic field are studied at field values characteristic for white dwarfs and pulsars. Calculated values of the energy levels and matrix elements of dipole and quadrupole moments of systems with an arbitrary nucleus charge Z in field interval 0.05Z 2 <or=B<or=Z 2 are given. The evolution of lines of equal electron density for hydrogen-like and helium-like systems as the field is increased is analysed. The helium-like system in a strong magnetic field was treated by perturbation theory for the inter-electron interaction.