A spectroscopic and photometric study of the planetary nebulae Kn 61 and Pa 5

Abstract

We present the first morpho-kinematical analysis of the planetary nebulae Kn 61 and Pa 5 and explore the nature of their central stars. Our analysis is based on high resolution and medium resolution spectroscopic observations, deep narrow-band imaging, and integral photometry. This material allows us to identify the morphological components and study their kinematics. The direct images and spectra indicate an absence of the characteristic [N II] and [S II] emission lines in both nebulae. The nebular spectrum of Kn 61 suggests an hydrogen deficient planetary nebula and the stellar spectrum of the central star reveals a hydrogen deficient PG 1159-type star. The [O III] position velocity diagram reveals that Kn 61 is a closed, empty, spherical shell with a thin border and a filamentary surface expanding at 67.6 km s$^{-1}$, and the shell is currently not expanding isotropically. We derived a kinematic age of $\sim$ 1.6$\times$10$^4$ yrs for an assumed distance of 4 kpc. A photometric period of $\sim$ 5.7($\pm$0.4) days has been detected for Kn 61, indicating presence of a possible binary system at its core. A possible link between filamentary, spherical shells and PG 1159-type stars is noted. The morphology of Pa 5 is dominated by an equatorial toroid and faint polar extensions. The equatorial region of this planetary nebula is expanding at 45.2 kms$^{-1}$. The stellar spectrum corresponds to a very hot star and is dominated by a steep blue rising continuum and He II, Balmer and Ca II photospheric lines.