Spectroscopy and shock modelling of the unusual bipolar outflow NGC 6905.

We present high and low resolution multi-slit spectroscopy, together with V, forbidden O III, and H-alpha narrow band imaging of the unusual bipolar outflow source NGC 6905. As a consequence, we are able to investigate the excitation structure of the source, the properties of the central star, and the projected kinematic structure of the outflow shell. Comparison of these results with simplified models of the source suggest that the outflow kinematics of the central shell and lobal extensions are likely to differ appreciably; and this, together with a variety of other evidence, suggests a model in which collimated winds are shock interacting with an enveloping halo. Such a mechanism would not only account for the morphology of the lobes, and the broad variations in surface brightness and excitation, but also matches the observed shell kinematics, and goes some way to explaining the location and characteristics of the associated ansae.