Kn 26, a new quadrupolar planetary nebula^⋆,⋆⋆

¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: mar@iaa.es
² Departamento de Física Aplicada, Facultade de Ciencias, Campus Lagoas-Marcosende s/n, Universidade de Vigo, 36310 Vigo, Spain
e-mail: lfm@iaa.es
³ Consejo Superior de Investigaciones Científicas (CSIC), c/ Serrano 117, 28006 Madrid, Spain
⁴ Instituto de Astronomía y Meteorología, Av. Vallarta No. 2602, Col. Arcos Vallarta, CP 44130 Guadalajara, Jalisco, Mexico
e-mail: gerardo@astro.iam.udg.mx
⁵ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, 22800 Ensenada, BC, Mexico
e-mail: vazquez@astro.unam.mx

Received: 18 October 2012
Accepted: 10 January 2013

Abstract

Once classified as an emission line source, the planetary nebula (PN) nature of the source Kn 26 has only recently been 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 lapse between the ejection of the two pairs of bipolar lobes is much shorter than their dynamical ages, implying a rapid change in 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 for type II PNe) and a high helium abundance (as for type I PNe), although not atypical among symbiotic stars. Such an anomalous chemical composition may have resulted from the curtailment of the time in the asymptotic giant branch by the evolution of the progenitor star through a common envelope phase.