Spitzer Mid-Infrared Observations of Seven Bipolar Planetary Nebulae

TL;DR

This study uses Spitzer Space Telescope data to analyze the mid-infrared structures of seven bipolar planetary nebulae, revealing extended emission, PAH features, and ring-like structures, advancing understanding of their composition and morphology.

Contribution

First detailed mid-infrared imaging and spectroscopy of seven bipolar planetary nebulae, highlighting PAH emission and structural features beyond previous optical studies.

Findings

Extended MIR emission at longer wavelengths

Flux ratios indicating PAH and dust contributions

Evidence of ring-like structures in NGC 2346

Abstract

We have investigated the mid-infrared (MIR) and visual structures of seven bipolar planetary nebulae (BPNe), using imaging and spectroscopy acquired using the Spitzer Space Telescope (SST), and the Observatorio Astronomico Nacional in Mexico. The results show that the sources are more extended towards longer MIR wavelengths, as well as having higher levels of surface brightness in the 5.8 and 8.0 microns bands. It is also noted that the 5.8/4.5 and 8.0/4.5 microns flux ratios increase with increasing distance from the nuclei of the sources. All of these latter trends may be attributable to emission by polycyclic aromatic hydrocarbons (PAHs) and/or warm dust continua within circum-nebular photo-dissociation regions (PDRs). A corresponding decrease in the flux ratios 8.0/5.8 microns may, by contrast, arise due to changes in the properties of the PAH emitting grains. We note evidence for possible 8.0 microns ring-like structures in the envelope of NGC 2346, located in a region beyond the minor axis limits of the ionized envelope. An analysis of the inner two rings shows that whilst they have higher surface brightnesses at longer MIR wavelengths, they are relatively stronger (compared to underlying emission) at 3.6 and 4.5 microns. There is also evidence for point reflection symmetry along the major axis of the outflow.