The "Principes de Asturias" nebula: A new quadrupolar planetary nebula from the IPHAS survey

Abstract

Context. The Isaac Newton Telescope Photometric Ha Survey (IPHAS) is currently mapping the Northern Galactic plane reaching to r′ = 20 mag with typically 1″ resolution. Hundreds of Planetary Nebulae (PNe), both point-like and resolved, are expected to be discovered. We report on the discovery of the first new PN from this survey: it is an unusual object located at a large galactocentric distance and has a very low oxygen abundance. Aims. Detecting and studying new PNe will lead to improved estimates of the population size, binary fraction and lifetimes, and yield new insights into the chemistry of the interstellar medium at large galactocentric distances. Methods. Compact nebulae are searched for in the IPHAS photometric catalogue, selecting those candidates with a strong Ha excess in the r′ - Hα vs. r′ - i′ colour-colour diagram. Searches for extended nebulae are by visual inspection of the mosaics of continuum-subtracted Hα images at a spatial sampling of 5 × 5 arcsec2. Follow-up spectroscopy enables confirmation of the PNe, and their physico-chemical study. Results. The first planetary nebula discovered via IPHAS imagery shows an intricate morphology: there is an inner ring surrounding the central star, bright inner lobes with an enhanced waist, and very faint lobular extensions reaching up to more than 100″. We classify it as a quadrupolar PN, a rather unusual class of planetary showing two pairs of misaligned lobes. From long-slit spectroscopy we derive Te[NII] = 12 800 ±1000 K, Ne = 390 ±40 cm-3, and chemical abundances typical of Peimbert's type I nebulae (He/H = 0.13, N/O = 1.8) with an oxygen abundanceof 12 + log(O/H) = 8.17 ±0.15. A kinematic distance of 7.0-3.0 +4.5kpc is derived, implying an unusually large size of >4 pc for the nebula. The photometry of the central star indicates the presence of a relatively cool companion. This, and the evidence for a dense circumstellar disk and quadrupolar morphology, all of which are rare among PNe, support the hypothesis that this morphology is related to binary interaction. © ESO 2006.