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M. W. Regan (STScI), P. J. Teuben (University of Maryland)
Nuclear star forming rings are found in many barred galaxies. In some of these galaxies the majority of the star formation is occurring in the ring. Although there is circumstantial evidence that an inner Lindblad resonance is required for the ring to form, very little work has been done on why this is so. In this talk we will present some of the first analytical work on why, where, and under what conditions rings form. By using both hydrodynamic simulations and numerically integrated stellar orbits we are able to show the relationship between the extent of the X2 orbit family and the nuclear ring radius. This provides the first clear evidence that the ring is formed by the conflict between gas on X2 orbits oriented perpendicular to the bar major axis and gas on X1 orbits oriented along the bar major axis.