COROTATION RESONANCE - UGC-2885 AND A NEW METHOD

Kinematic data on the minor axis of the giant spiral galaxy UGC 2885 show a change in the sign of the radial velocity across spiral arms. Such a sign change indicates that corotation has been crossed. In fact, two sign changes are seen, implying that there are two spiral patterns. The morphology of the galaxy supports this interpretation. A general method is also presented that can be used to locate the corotation resonance in a grand design spiral galaxy. The method relies on the effects of geometric phase, and assumes only that the spiral flow is wave based and periodic in azimuth.