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

TL;DR

This paper provides a detailed kinematic analysis of the planetary nebula Hb 12, revealing high-speed knots, their velocities, and the nebula's inclination, offering insights into its structure and formation history.

Contribution

It presents the first detection of end cap knots in Hb 12, measures their velocities, and discusses the nebula's inclination and potential multiple outburst origins.

Findings

Detection of end cap knots aligned with bipolar lobes.

Measurement of radial velocities around 120 km/s for knots.

Discovery of high-velocity knots with Hubble-type velocities.

Abstract

We present a detailed kinematical analysis of the young compact hourglass-shaped planetary nebula Hb 12. We performed optical imaging and longslit spectroscopy of Hb 12 using the Manchester echelle spectrometer with the 2.1m 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 [NII]6584 image of Hb 12. We measured from our spectroscopy radial velocities of 120 km/s for these knots. We have derived the inclination angle of the hourglass shaped nebular shell to be 65 degrees to the line of sight. It has been suggested that Hb 12's central star system is an eclipsing binary (Hsia et al. 2006) 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 Halpha 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.