THE DARK HALO OF THE POLAR-RING GALAXY NGC-4650A

By analyzing the rotation of its central disk and outer polar ring, we place limits on the flattening of the unseen halo of the galaxy NGC 4650A. We fit a model consisting of a bulge, disk, axisymmetric dark halo, and massive polar ring to both rotation curves and show that the observations are consistent with a range of halo flattening, from spherical to as flat as an E8 elliptical galaxy. The best fits are obtained for dark halo flattenings in the range E3-E7. The substantial mass of the ring is probably responsible for a characteristic "wiggle" in the polar rotation curve; fits to this feature suggest that there may be considerably more mass in the ring than has been reported from neutral hydrogen measurements.