KINEMATICS AND ORIGIN OF THE RINGED BIPOLAR NEBULA MZ-1

High resolution, spatially resolved measurements of the H alpha, [NII] 6584 Angstrom and [SII] emission lines of the bipolar planetary nebul a Mz 1 have been obtained with the Manchester Echelle Spectrometer on the Anglo-Australian telescope. The echelle profiles for slit position s that cross the central nebular core have been analysed and related t o a previously obtained CCD image of the region. A well defined 'ring like' structure, readily apparent in our H alpha + [NII] image, is sho wn to be expanding with the main bulk of the nebula at 23 km s(-1) and in a manner which is well represented by a cylindrical model with exp ansion velocities proportional to the radial distance from centre to c ylinder edge. The dynamical lifetime of the nebula is of the order of 7,000 years. Estimates of the electron density from [SII] emission-lin e ratios suggest a density in the ring of order 1700 cm(-3) compared t o 400 cm(-3) in the rest of the nebular core. Combining this result wi th IRAS measurements, we estimate a mass of the nebula of order 0.5 M- .. We discuss the probable origin and history of the nebula in terms o f interacting stellar winds and consider the bipolar nebula as having been formed either via a fast wind in an aspherical density distributi on, or through a superwind confined by an equatorial disc. In either c ase a relatively high mass-loss rate (greater than or equal to 5 x 10( -5) M(.)yr(-1)) is inferred for the superwind phase prior to the exist ence of a fast wind phase of the current central star.