The Unusual Distributions of Ionized Material and Molecular Hydrogen in NGC 6881: Signposts of Multiple Events of Bipolar Ejection in a Planetary Nebula

Abstract

The planetary nebula NGC 6881 displays in the optical a quadrupolar morphology consisting of two pairs of highly collimated bipolar lobes aligned along different directions. An additional bipolar ejection is revealed by the hydrogen molecular emission, but its wide hourglass morphology is very different from that of the ionized material. To investigate in detail the spatial distribution of molecular hydrogen and ionized material within NGC 6881, and to determine the prevalent excitation mechanism of the H2 emission, we have obtained new near-IR Br-gamma and H2 and optical H-alpha and [N II] images, as well as intermediate resolution JHK spectra. These observations confirm the association of the H2 bipolar lobes to NGC 6881 and find that the prevalent excitation mechanism is collisional. The detailed morphology and very different collimation degree of the H2 and ionized bipolar lobes of NGC 6881 not only imply that multiple bipolar ejections have occurred in this nebula, but also that the dominant shaping agent is different for each bipolar ejection: a bipolar stellar wind most likely produced the H2 lobes, while highly collimated outflows are carving out the ionized lobes into the thick circumstellar envelope. The asymmetry between the southeast and northwest H2 bipolar lobes suggests the interaction of the nebula with an inhomogeneous interstellar medium. We find evidence that places NGC 6881 in the H II region Sh 2-109 along the Orion local spiral arm.

arXiv comment9 pages, 7 figures, 4 tables

References in corpus (13)

• Northern JHK Standard Stars for Array Detectors
• Investigating the Near-Infrared Properties of Planetary Nebula II. Medium Resolution Spectra
• Revealing the Photodissociation Region: Hubble Space Telescope/NICMOS Imaging of NGC 7027
• Why Magnetic Fields Cannot be the Main Agent Shaping Planetary Nebulae
• Rings in the Haloes of Planetary Nebulae
• Investigating the Near-Infrared Properties of Planetary Nebulae. I. Narrowband Images
• H2 and Br-gamma narrow-band imaging of bipolar planetary nebulae
• Menzel 3: Dissecting the ant
• A Butterfly in the Making: Revealing the Near- Infrared Structure of Hubble 12
• Multiple Collimated Outflows in the Proto-planetary Nebula GL 618
• Multiple Molecular H2 Outflows in AFGL 618
• Mz 3, a Multipolar Nebula in the Making
• Kinematic Structure of H2 and [Fe II] in the Bipolar Planetary Nebula M 2-9

Cited by in corpus (17)

• Abell 41: shaping of a planetary nebula by a binary central star?
• Extended Structures of Planetary Nebulae Detected in H${}_2$ Emission
• Rings and Halos in the Mid-Infrared: The Planetary Nebulae NGC 7354 and NGC 3242
• The Halos of Planetary Nebulae in the Mid-Infrared: Evidence for Interaction with the Interstellar Medium
• H${}_2$ emission in the low-ionisation structures of the Planetary Nebulae NGC 7009 and NGC 6543
• Spitzer mid-infrared spectroscopic observations of planetary nebulae
• Multipolar Planetary Nebulae: Not as Geometrically Diversified as Thought
• The Halo and Rings of the Planetary Nebula NGC 40 in the Mid-Infrared
• The excitation mechanism of H2 in bipolar planetary nebulae
• Pushing the limits: detecting H2 emission from faint bipolar planetary nebulae in the IPHAS sample
• Optical and Mid-Infrared Observations of the Planetary Nebula NGC 6781
• VLT observations of the asymmetric Etched Hourglass Nebula, MyCn 18
• The morpho-kinematical structure and chemical abundances of the complex planetary nebula NGC 1514
• Morphological study of the nested planetary nebula Hubble 12
• A distance estimate based on angular expansion for the planetary nebula NGC 6881
• Discovery of Raman-scattered He II $\lambda$6545 in the Planetary Nebulae NGC 6886 and NGC 6881
• The Effect of the Slit Configuration on the H${}_2$ 1-0~S(1) to Br$\gamma$ Line Ratio of Spatially Resolved Planetary Nebulae