High-speed knots in the hourglass-shaped planetary nebula Hubble 12

We present a detailed kinematical analysis of the young compact hourglass-shaped planetary nebula Hb 12. We performed optical imaging and long-slit spectroscopy of Hb 12 using the Manchester echelle spectrometer with the 2.1-m San Pedro Martir telescope. We reveal, for the first time, the presence of end caps (or knots) aligned with the bipolar lobes of the planetary nebula shell in a deep [N ii] lambda 6584 image of Hb 12. We measured from our spectroscopy radial velocities of similar to 120 km s(-1) for these knots. We have derived the inclination angle of the hourglass-shaped nebular shell to be similar to 65 degrees to the line of sight. It has been suggested that Hb 12's central star system is an eclipsing binary which would imply a binary inclination of at least 80 degrees. However, if the central binary has been the major shaping influence on the nebula, then both nebula and binary would be expected to share a common inclination angle. Finally, we report the discovery of high-velocity knots with Hubble-type velocities, close to the core of Hb 12, observed in H alpha and oriented in the same direction as the end caps. Very different velocities and kinematical ages were calculated for the outer and inner knots showing that they may originate from different outburst events.