Optical and Mid-Infrared Observations of the Planetary Nebula NGC 6781

Abstract

Although the planetary nebula NGC 6781 appears to possess an elliptical morphology, its kinematic and emission characteristics are in many ways unusual, and it is possible that it may represent a bipolar source oriented close to the line of sight. We shall present deep imaging of this nebula in [O III], Ha and [N II], and using broad-band (F555W and F814W) filters. These were taken with the 2.56-m Nordic Optical Telescope and Hubble Space Telescope. This is combined with mid-infrared (MIR) imaging and spectroscopy acquired with the Spitzer Space Telescope (Spitzer), and near-infrared spectroscopy deriving from the Infrared Space Observatory (ISO). These reveal details of the complex [N II] structure associated with extended shell emission, perhaps associated with highly inclined bipolar lobes. We also note the presence of narrow absorbing filaments and clumps projected against the surface of the envelope, components which may be responsible for much of the molecular emission. We point out that such clumps may be responsible for complex source structure in the MIR, and give rise to asymmetries in emission along the major axis of the source.

arXiv comment12 pages, 10 figures, Accepted for publication in MNRAS. 32 pages in arXiv

References in corpus (8)

• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• The Infrared Spectrograph on the Spitzer Space Telescope
• Investigating the Near-Infrared Properties of Planetary Nebula II. Medium Resolution Spectra
• The Near-Infrared Structure and Spectra of the Bipolar Nebulae M 2--9 and Afgl 2688: The Role of UV-Pumping and Shocks in Molecular Hydrogen Excitation
• A Butterfly in the Making: Revealing the Near- Infrared Structure of Hubble 12
• 3-D Photoionization Structure and Distances of Planetary Nebulae III. NGC 6781
• The Unusual Distributions of Ionized Material and Molecular Hydrogen in NGC 6881: Signposts of Multiple Events of Bipolar Ejection in a Planetary Nebula
• A search for CO+ in planetary nebulae

Cited by in corpus (8)

• H${}_2$ in low-ionization structures of planetary nebulae
• The Herschel Planetary Nebula Survey (HerPlaNS) I. Data Overview and Analysis Demonstration with NGC 6781
• The Herschel Planetary Nebula Survey (HerPlaNS) - a comprehensive dusty photoionization model of NGC6781
• Extended Structures of Planetary Nebulae Detected in H${}_2$ Emission
• Herschel Planetary Nebula Survey (HerPlaNS) - First Detection of OH+ in Planetary Nebulae
• Spitzer mid-infrared spectroscopic observations of planetary nebulae
• A Herschel study of NGC 650
• The Structure of the Planetary Nebula NGC 2371 in the Visible and Mid-Infrared