The expansion proper motions of the extraordinary giant lobes of the planetary nebula KjPn 8 revisited

TL;DR

This study measures the expansion proper motions of KjPn 8's giant lobes to determine its distance, ages, and energy, revealing sequential ejection and an energetic outflow consistent with an ILOT event.

Contribution

It provides the first firm distance measurement and age estimates for KjPn 8's lobes using proper motions over a 57-year baseline, and links the energetic outflow to an ILOT event.

Findings

Distance to KjPn 8 is 1.8 ± 0.3 kpc.

Dynamical ages of lobes are 3200, 7200, and ≥50,000 years.

Kinetic energy of the youngest outflow is ~10^47 erg.

Abstract

The primary aim is to establish a firm value for the distance to the extraordinary planetary nebula KjPn 8. Secondary aims are to measure the ages of the three giant lobes of this object as well as estimate the energy in the eruption, that caused the most energetic outflow, for comparison with that of an intermediate luminosity optical transient (ILOT). For these purposes a mosaic of images in the Halpha+[N II] optical emission lines has been obtained with the new Aristarchos telescope in 2011 for comparison with the images of the KjPn 8 giant lobes present on the POSSI-R 1954 and POSSII-R 1991 plates. Expansion proper motions of features over this 57 yr baseline in the outflows are present. Using these, a firm distance to KjPn 8 of 1.8 +- 0.3 kpc has been derived for now the angle of the latest outflow to the sky has been established from HST imagery of the nebular core. Previously, the uncertain predictions of a bow-shock model were used for this purpose. The dynamical ages of the three separate outflows that form the giant lobes of KjPn 8 are also directly measured as 3200, 7200 and >= 5x10^4 yr respectively which confirms their sequential ejection. Moreover, the kinetic energy of the youngest and most energetic of these is measured as ~10^47 erg which is compatible with an ILOT origin.