# Search for Polycyclic Aromatic Hydrocarbons in the Outflows from Dust-Producing Wolf-Rayet Stars

## TL;DR

This study investigates the presence and characteristics of polycyclic aromatic hydrocarbons (PAHs) in the dust outflows of Wolf-Rayet stars using mid-infrared spectra, revealing diverse PAH features and their potential role in dust formation.

## Contribution

It provides the first detailed analysis of PAH signatures in Wolf-Rayet star outflows, highlighting variations in PAH features among different systems and suggesting PAHs as precursors to amorphous carbon dust.

## Key findings

- Detection of PAH emission features around 6.5, 8.0, and 8.8 μm.
- Absence of the 7.7 μm PAH band in WR19.
- Presence of large, neutral PAHs in WR118.

## Abstract

A combined mid-IR spectrum of five colliding-wind, massive, dust-producing Population I Wolf-Rayet (WR) binaries shows a wealth of absorption and emission details coming from the circumstellar dust envelopes, as well as from the interstellar medium. The prominent absorption features may arise from a mix of interstellar carbonaceous grains formed in high- (e.g., 3.4, 6.8, 7.2 $\mu$m) and low-temperature (3.3, 6.9, 9.3 $\mu$m) environments. The broad emission complexes around $\sim$6.5, 8.0 and 8.8 $\mu$m could arise from ionized, small polycyclic aromatic hydrocarbon (PAH) clusters and/or amorphous carbonaceous grains. As such these PAH emissions may represent the long sought after precursors of amorphous Carbon dust. We also detect a strong $\sim$10.0 $\mu$m emission in the spectra of WR48a and WR112, that we tentatively link to ionized PAHs. Upon examining the available archival spectra of prodigious individual WR dust sources, we notice a surprising lack of 7.7 $\mu$m PAH band in the spectrum of the binary WR19, in contrast to the apparent strength of the 11.2, 12.7 and 16.4 $\mu$m PAH features. Strong PAH emissions are also detected in the $\lambda>$10 $\mu$m spectrum of another dust-producing system, WR118, pointing to the presence of large, neutral, presumably interstellar PAH molecules towards WR19 and WR118.