Ionized haloes in planetary nebulae: new discoveries, literature compilation and basic statistical properties

Abstract

We present a comprehensive observational study of haloes around planetary nebulae (PNe). Deep Hα+[N ii] and/or [O iii] narrow‐band images have been obtained for 35 PNe, and faint extended haloes have been newly discovered in the following 10 objects: Cn 1‐5, IC 2165, IC 2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, and possibly IC 1747. New deep images have also been obtained of other known or suspected haloes, including the huge extended emission around NGC 3242 and Sh 2‐200. In addition, the literature was searched, and together with the new observations an improved data base containing some 50 PN haloes has been compiled. The halo sample is illustrated in an image atlas contained in this paper, and the original images are made available for use by the scientific community at http://www.ing. iac.es/∼rcorradi/HALOES/. The haloes have been classified following the predictions of modern radiation‐hydrodynamical simulations that describe the formation and evolution of ionized multiple shells and haloes around PNe. According to the models, the observed haloes have been divided into the following groups: (i) circular or slightly elliptical asymptotic giant branch (AGB) haloes, which contain the signature of the last thermal pulse on the AGB; (ii) highly asymmetrical AGB haloes; (iii) candidate recombination haloes, i.e. limb‐brightened extended shells that are expected to be produced by recombination during the late post‐AGB evolution, when the luminosity of the central star drops rapidly by a significant factor; (iv) uncertain cases which deserve further study for a reliable classification; (v) non‐detections, i.e. PNe in which no halo is found to a level of ≲10−3 the peak surface brightness of the inner nebulae. We discuss the properties of the haloes: detection rate, morphology, location of the central stars in the Hertzsprung–Russell diagram, sizes, surface brightness profiles, and kinematical ages. Among the most notable results, we find that, as predicted by models, ionized AGB haloes are a quite common phenomenon in PNe, having been found in 60 per cent of elliptical PNe for which adequately deep images exist. Another 10 per cent show possible recombination haloes. In addition, using the kinematical ages of the haloes and inner nebulae, we conclude that most of the PNe with observed AGB haloes have left the AGB far from a thermal pulse, at a phase when hydrogen burning is the dominant energy source. We find no significant differences between the AGB haloes of hydrogen‐poor and hydrogen‐rich central stars.

Binary planetary nebulae nuclei towards the Galactic bulge

“…Measuring 8 ′′ across the outer shell is more than twice the 3.5 ′′ diameter of the inner shell and the western side appears to be brightened by interaction with the ISM. The eastern edge of the outer shell has an intensity 30-45% that of the inner shell, far too bright to be a true halo which would be considerably fainter (Corradi et al 2003). We measured a similar intensity ratio for the outer shell of M 2-2 from the Hα IAC catalogue image (Manchado et al 1996a).…”

“…Bond & Livio (1990) favoured multiple mass ejections on the tip of the AGB to explain the absence of MSPNe in their sample because the CE phase would interrupt such a scenario. We now know that the simplest double-shell PN requires only a combination of photo-ionisation and wind interaction (Schönberner et al 1997;Corradi et al 2003) and this favours the existence of at least some MSPNe with binary nuclei.…”

Physical Structure of the Planetary Nebula NGC 3242 From the Hot Bubble to the Nebular Envelope

“…These two shells are further enclosed by arcs and a giant broken halo revealed by deep images (Corradi et al 2003(Corradi et al , 2004. The double-shell morphology of the main nebula of NGC 3242 is highly suggestive of interactions between the fast stellar wind of its central star (v ∞ =2,400 km s −1 , Pauldrach et al 2004) and the previous slow AGB wind.…”

The influence of diffuse scattered light

“…Extended and faint ionized haloes around planetary nebulae (PNe) are affected by scattered light from the drastically brighter central parts (Middlemass et al 1989); the authors do not measure a PSF by themselves, but analyse their data of BD+30 • 3639 with the extended PSF of King (1971, hereafter K71). Other studies search deep exposures of A&A 567, A97 (2014) PNe for additional haloes (e.g., Corradi et al 2003), focusing on observations that show clumps and asymmetries, and avoiding data that only show diffuse light. With few exceptions these studies do not derive any physical properties of the haloes.…”