Kn 26, a New Quadrupolar Planetary Nebula

TL;DR

Kn 26 is a newly identified quadrupolar planetary nebula with complex bipolar lobes, unusual chemical composition, and evidence of rapid changes in its central engine's ejection direction, expanding understanding of nebula morphologies.

Contribution

This study provides the first detailed morphological, kinematic, and chemical analysis of Kn 26, establishing it as a quadrupolar planetary nebula with unique properties.

Findings

Kn 26 exhibits an hourglass bipolar morphology with a second pair of lobes.

The nebula shows a low N/O ratio and high helium abundance, unusual for PNe.

Rapid changes in ejection direction suggest dynamic central engine activity.

Abstract

Once classified as an emission line source, the planetary nebula (PN) nature of the source Kn 26 has been only recently recognized in digital sky surveys. To investigate the spectral properties and spatio-kinematical structure of Kn 26, we have obtained high spatial-resolution optical and near-IR narrow-band images, high-dispersion long-slit echelle spectra, and intermediate-resolution spectroscopic observations. The new data reveal an hourglass morphology typical of bipolar PNe. A detailed analysis of its morphology and kinematics discloses the presence of a second pair of bipolar lobes, making Kn 26 a new member of the subclass of quadrupolar PNe. The time-lap between the ejection of the two pairs of bipolar lobes is much smaller than their dynamical ages, implying a rapid change of the preferential direction of the central engine. The chemical composition of Kn 26 is particularly unusual among PNe, with a low N/O ratio (as of type II PNe) and a high helium abundance (as of type I PNe), although not atypical among symbiotic stars. Such an anomalous chemical composition may have resulted from the curtail of the time in the Asymptotic Giant Branch by the evolution of the progenitor star through a common envelope phase.