1998A&A...334..670M

The remarkable velocity structure of the different components of the hydrogen-deficient planetary nebula Abell 78 have been revealed by obtaining spatially resolved profiles of the [O III] 5007Å line with the Manchester echelle spectrometer combined with the 2.1m San Pedro Martir telescope. The outer, diffuse, hydrogen-rich, 124" diameter shell is expanding radially at 40km/s. The irregular, knotty, hydrogen-deficient 89x52" inner shell has a similar overall expansion velocity but more complex kinematical structure. Similar to A 30, velocity `spikes' are found in the position-velocity arrays of [O III] 5007Å profiles from the inner shell. These extend to a further -140km/s than the radial velocity of the approaching side of this inner shell. The [O III] 5007Å bright, hydrogen-deficient core knots are distributed throughout an elongated disk expanding at ≃25km/s. There is kinematical evidence that `polar bullets' are being ejected perpendicularly to this central feature at 380km/s. Altogether `velocity spikes' and other high-speed knots in the pv arrays of [O III] 5007Å profiles are found over a 455km/s range of radial velocities. Many of the kinematical phenomena are considered to be a consequence of the mass-loaded, shocked, wind from the central star.