Instituto de Astrofísica de Andalucía (IAA-CSIC),
Glorieta de la Astronomía s/n,
2 Departamento de Física Aplicada, Facultade de Ciencias, Campus Lagoas-Marcosende s/n, Universidade de Vigo, 36310 Vigo, Spain
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
5 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, 22800 Ensenada, BC, Mexico
Received: 18 October 2012
Accepted: 10 January 2013
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.
Key words: infrared: ISM / planetary nebulae: general / planetary nebulae: individual: Kn 26 / stars: AGB and post-AGB
Based on observations made with the Nordic Optical Telescope (NOT) and the William Herschel Telescope (WHT) on the island of La Palma in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC), the 2.1-m telescope of the Observatorio Astronómico Nacional at the Sierra de San Pedro Mártir (OAN-SPM), and the 1.5-m telescope at the Observatorio de Sierra Nevada (OSN), Granada, Spain. NOT is operated jointly by Denmark, Finland, Iceland, Norway, and Sweden. WHT is operated by the Isaac Newton Group. The 2.1-m telescope at the OAN-SPM is a national facility operated by the Instituto de Astronomía of the Universidad Nacional Autónoma de México. The 1.5-m telescope at the OSN is operated by the Instituto de Astrofísica de Andalucía (IAA).The data presented here were obtained in part with ALFOSC, which is provided by the IAA under a joint agreement with the University of Copenhagen and NOTSA.
FITS files for spectra and images are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A53
© ESO, 2013