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

TL;DR

This study presents multi-wavelength optical and infrared observations of planetary nebula NGC 6781, revealing complex structures, bipolar lobes, and clumps that influence its emission characteristics and morphology.

Contribution

It provides detailed imaging and spectroscopic analysis across optical and infrared wavelengths, uncovering complex structures and potential bipolar features in NGC 6781.

Findings

Detection of extended shell emission and bipolar lobes.

Identification of narrow absorbing filaments and clumps.

Insights into the complex emission structure and asymmetries.

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.