On the Formation of Elliptical Rings in Disk Galaxies
  N-body simulations of galactic collisions are employed to investigate the
formation of elliptical rings in disk galaxies. The relative inclination
between disk and dwarf galaxies is studied with a fine step of five degrees. It
is confirmed that the eccentricity of elliptical ring is linearly proportional
to the inclination angle. Deriving from the simulational results, an analytic
formula which expresses the eccentricity as a function of time and inclination
angle is obtained. This formula shall be useful for the interpretations of the
observations of ring systems, and therefore reveals the merging histories of
galaxies.
