GALACTIC BARS WITH CENTRAL MASS CONCENTRATIONS - 3-DIMENSIONAL DYNAMICS

The stellar dynamics at the transitions between a strongly barred and rotating potential and a spherical and dense central mass concentratio n is investigated in a model potential. Three different degrees of con centration of the central mass are studied. The main families of three -dimensonal periodic orbit are found by numerical means. The structure of phase space is presented by bifurcation diagrams and surfaces of s ection. A large region of instability develops near the inner Lindblad resonance (ILR) due to the strong bar potential. In such a mass confi guration the radial ILR is typically near the corresponding vertical I LR, consequently the instability of orbits is radial as well as vertic al, helping the heating of disk stars into a bulge. These secular evol ution processes from barred to unbarred and in the direction of increa sing the bulge-to-disk ratio should affect the evolution of galaxies o ver a Hubble time.