SIMBAD references

High resolution, spatially resolved measurements of the Hα, [NII] 6584 Å and [SII] emission lines of the bipolar planetary nebula Mz 1 have been obtained with the Manchester Echelle Spectrometer on the Anglo-Australian telescope. The echelle profiles for slit positions that cross the central nebular core have been analysed and related to a previously obtained CCD image of the region. A well defined `ring like' structure, readily apparent in our Hα + [NII] image, is shown to be expanding with the main bulk of the nebula at 23km/s and in a manner which is well represented by a cylindrical model with expansion velocities proportional to the radial distance from centre to cylinder edge. The dynamical lifetime of the nebula is of the order of 7,000 years. Estimates of the electron density from [SII] emission-line ratios suggest a density in the ring of order 1700cm^–3 compared to 400cm^–3 in the rest of the nebular core. Combining this result with 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 of interacting stellar winds and consider the bipolar nebula as having been formed either via a fast wind in an aspherical density distribution, or through a superwind confined by an equatorial disc. In either case a relatively high mass-loss rate (≥5x10^–5M_☉/yr) is inferred for the superwind phase prior to the existence of a fast wind phase of the current central star.