Chemical Abundances and Dust in Planetary Nebulae in the Galactic Bulge

TL;DR

This study uses mid-infrared spectra to determine elemental abundances and dust properties of planetary nebulae in the Galactic Bulge, revealing differences from Disk nebulae and insights into Bulge evolution.

Contribution

First infrared-based abundance measurements of Bulge planetary nebulae, highlighting their unique dust features and chemical evolution compared to the Disk.

Findings

Bulge nebulae have slightly higher elemental abundances than Disk nebulae.

Oxygen-rich crystalline silicates dominate Bulge nebulae dust features.

Approximately half of Bulge nebulae show carbon-rich dust features.

Abstract

We present mid-infrared Spitzer spectra of eleven planetary nebulae in the Galactic Bulge. We derive argon, neon, sulfur, and oxygen abundances for them using mainly infrared line fluxes combined with some optical line fluxes from the literature. Due to the high extinction toward the Bulge, the infrared spectra allow us to determine abundances for certain elements more accurately that previously possible with optical data alone. Abundances of argon and sulfur (and in most cases neon and oxygen) in planetary nebulae in the Bulge give the abundances of the interstellar medium at the time their progenitor stars formed; thus these abundances give information about the formation and evolution of the Bulge. The abundances of Bulge planetary nebulae tend to be slightly higher than those in the Disk on average, but they do not follow the trend of the Disk planetary nebulae, thus confirming the difference between Bulge and Disk evolution. Additionally, the Bulge planetary nebulae show peculiar dust properties compared to the Disk nebulae. Oxygen-rich dust feature (crystalline silicates) dominate the spectra of all of the Bulge planetary nebulae; such features are more scarce in Disk nebulae. Additionally, carbon-rich dust features (polycyclic aromatic hydrocarbons) appear in roughly half of the Bulge planetary nebulae in our sample, which is interesting in light of the fact that this dual chemistry is comparatively rare in the Milky Way as a whole.