New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge

TL;DR

This study identifies new groups of planetary nebulae in the Galactic bulge with peculiar dust chemistry, revealing complex dust compositions and challenging existing evolutionary models.

Contribution

It introduces a new classification of planetary nebulae based on dust properties and demonstrates that dual-dust chemistry occurs beyond emission-line central star nebulae.

Findings

Identification of three sub-groups with distinct dust compositions

Dual-dust chemistry is present in nebulae without emission-line central stars

Some nebulae show unusual gas chemical compositions that challenge standard evolution models

Abstract

We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates. We find that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the common view of planetary nebulae. In particular, it is challenging to interpret the peculiar gas chemical composition of many analyzed objects in the standard picture of the evolution of planetary nebulae progenitors. We confirm that the dual-dust chemistry phenomenon is not limited to planetary nebulae with emission-line central stars.