Rings and Halos in the Mid-Infrared: The Planetary Nebulae NGC 7354 and NGC 3242

TL;DR

This study uses Spitzer Space Telescope images to reveal and analyze halos and rings in two planetary nebulae, NGC 7354 and NGC 3242, providing new observations of these features in the mid-infrared.

Contribution

First mid-infrared detection of halos and rings in NGC 7354, with analysis linking halo formation to radiatively accelerated mass loss in AGB progenitors.

Findings

Halos and rings observed in NGC 3242 and NGC 7354.

Halo density fall-offs produce brightness gradients matching observations.

Results support models of mass loss during late stellar evolution.

Abstract

We present images of the planetary nebulae (PNe) NGC 7354 and NGC 3242 in four mid-infrared (MIR) photometric bands centred at 3.6, 4.5, 5.8 and 8.0 microns; the results of observations undertaken using the Spitzer Space Telescope (SST). The resulting images show the presence of a halo and rings in NGC 3242, as previously observed through narrow band imaging at visual wavelengths, as well as evidence for a comparable halo and ring system in NGC 7354. This is the first time that a halo and rings have been observed in the latter source. We have analysed the formation of halos as a result of radiatively accelerated mass loss in the AGB progenitors. Although the models assume that dust formation occurs in C-rich environments, we note that qualitatively similar results would be expected for O-rich progenitors as well. The model fall-offs in halo density are found to result in gradients in halo surface brightness which are similar to those observed in the visible and MIR.