Extended Structures of Planetary Nebulae Detected in H₂ Emission^∗

Abstract

We present narrowband near-infrared images of a sample of 11 Galactic planetary nebulae (PNe) obtained in the H 2 2.122 μm and Brγ 2.166 μm emission lines and the K c 2.218 μm continuum. These images were collected with the Wide-field Infrared Camera on the 3.6 m Canada-France-Hawaii Telescope (CFHT); their unprecedented depth and wide field of view allow us to find extended nebular structures in H 2 emission in several PNe, some of these being the first detection. The nebular morphologies in H 2 emission are studied in analogy with the optical images, and indication of stellar wind interactions is discussed. In particular, the complete structure of the highly asymmetric halo in NGC 6772 is witnessed in H 2 , which strongly suggests interaction with the interstellar medium. Our sample confirms the general correlation between H 2 emission and the bipolarity of PNe. The knotty or filamentary fine structures of the H 2 gas are resolved in the inner regions of several ring-like PNe, also confirming the previous argument that H 2 emission mostly comes from knots or clumps embedded within fully ionized material at the equatorial regions. Moreover, the H 2 image of the butterfly-shaped Sh 1-89, after removal of field stars, clearly reveals a tilted ring structure at the waist. These high-quality CFHT images justify follow-up detailed morphokinematic studies that are desired in order to deduce the true physical structures of a few PNe in the sample.

H2 emission in the low-ionization structures of the planetary nebulae NGC 7009 and NGC 6543

“…Similar to NGC 7009, halo features in NGC 6543 also appear with green colour in the three-colours RGB IRAC images ( fig. 1 and 9 in Hora et al 2004;Fang et al 2018). As we have already pointed out, the strong emission from the [4.5] band is attributed to molecular lines that fall within this band (Hora et al 1999;De Buizer & Vacca 2010).…”

“…Couple of years later, Akras, Gonçalves and Ramos-Larios (2017) succeed to detect the H 2 emission from the LISs in two PNe, K 4-47 and NGC 7662, using very deep narrow-band imagery from the 8 m Gemini North telescope. Fang et al (2018) reported the detection of H 2 emission from two distant pairs of knots in Hb 12, from a number of randomly distributed knots in the haloes of NGC 6543 and NGC 7009 as well as from the pair of LISs in the ionized region of NGC 7009. Regarding Hb 12, it should be mentioned that despite the H 2 from its distant clumps, strong H 2 1-0 S(1) emission has also been detected in the centre of the nebula (Dinerstein et al 1988;Ramsay et al 1993;Luhman & Rieke 1996), and its origin is pure UV-fluorescence.…”

X-ray Shaping of Planetary Nebulae

“…These new models show the relevance of turbulent mixing and heat conduction on the evolution of the hot gas in PNe [39]. Rayleigh-Taylor instabilities at the interface are shown to be responsible for shadowing instabilities, which have notable effects in the mid-IR (dust) and near-IR H 2 (molecular) morphologies [6]. Future multi-dimensional hydro-dynamical models will need to account also for faster and brighter CSPN evolutionary tracks [25].…”

“…The brightest lines in this spectrum are associated with highly ionized (H-and He-like) species of C, O, Ne, such as O VIII λ18.97, C VI λ33. 6 These high-dispersion grating X-ray spectroscopic observations are at the technical limit of Chandra and XMM-Newton. All other X-ray-emitting PNe are fainter or have lower surface brightness than of BD+30 • 3639 and NGC 6543.…”

Numerical simulations of wind-driven protoplanetary nebulae. II. signatures of atomic emission

“…Near-infrared observations have broadened our knowledge of PPN in which H2 emission has been mapped and compared to the atomic emission (Fang et al 2018a). It has also been found that a large fraction of PN may remain undetected in the optical, requiring H2 imaging surveys (Gledhill et al 2018).…”