Evidence for contraction in the nuclear ring of the barred spiral galaxy NGC 3351

The nucleus of the barred spiral galaxy NGC 3351 consists of a ring of low-excitation H II regions. Line-of-sight velocities around the ring indicate a well-defined sinusoid, but with maximum and minimum velocities displaced about 20 deg from that predicted from the geometry of the outer galaxy. One simple interpretation is that the nuclear ring is a circle in the plane of the galaxy which is rotating and contracting with a rotational velocity of about 126 km/s and a contraction rate of about 34 km/s at a distance of 340 pc. Other possible interpretations are also discussed.