Echelle observations of high-velocity lobes projecting from the core of the bipolar nebula MZ-3.

New observations with the Manchester echelle spectrometer on the AAT have revealed an outer lobe and a region of high-velocity, diffuse gas projecting from the dense ionized and neutral disk in the core of the bipolar nebula MZ-3. Profiles of the interstellar Na I lines show the neutral disk to be expanding at about 20 km/s. A model of MZ-3 is presented in which inner, bright, approximately spherical lobes expand radially at 50 km/s on either side of the central disk which obscures the ionizing star. Surrounding these inner bright lobes are faint outer lobes which are elongated along axes tilted toward and away from the observer. Over the centers of these regions the lines are split by 100 km/s, but systematically converge back to a single profile at their edges. The faintest outer lobe appears to contain these two inner ones on the southern side of the core and to be of much higher velocity for the line profiles are 450 km/s in extent over its center. Periodic ejections of shells from a star in a protoplanetary phase are favored as explanations of these observations, rather than collimated flows driven by an energetic stellar wind from a central star. However, the latter mechanism is not completely discounted for both MZ-3 and the comparable nebula NGC 6302.