Galaxy models with live halos

Computer models of galaxies are described, in which the disc stars and the halo stars are both treated fully self consistently. These were used to test the validity of the 'rigid halo' approximation usually employed when studying the instabilities of a disc of stars. The models show that very little interaction between the populations occurs while the disc remains nearly axisymmetric, but a strong bar is able to transfer angular momentum from the disc to the halo. The global bar stability of the disc is not greatly affected by the interaction between the two stellar populations, and it is found that a large fraction of the total galactic mass is still required in the spheroidal component if bar formation is to be prevented. (36 refs).