Detection of a broad 8 $\mu$m UIR feature in the mid-infrared spectrum of WR 125 observed with Subaru/COMICS

TL;DR

This study reports the detection of a broad 8 μm infrared feature in the dust around the Wolf-Rayet star WR 125, comparing it with other WC stars and analyzing the impact of extinction correction on this feature.

Contribution

The paper identifies a broad 8 μm UIR feature in dusty WC stars and revises the dust formation period of WR 125, providing new insights into dust formation in Wolf-Rayet binaries.

Findings

Broad 8 μm feature detected in WR 125 and other WC stars

Feature likely related to Class C UIR features

Revised dust formation period of WR 125 to 28.1 years

Abstract

We present the detection of a broad 8 $\mu$m feature in newly formed dust around the carbon-rich Wolf-Rayet (WC) binary WR 125 from N-band low-resolution (NL; R$\sim$250) spectroscopy between 7.3-13.6 $\mu$m and N-band (11.7 $\mu$m) and Q-band (18.8 $\mu$m) imaging with Subaru/COMICS in 2019 October. WR 125 is a colliding wind binary (${\rm WC7+O9}$) that exhibited renewed dust formation starting in 2018, $\sim$28 years after its first dust formation episode had been observed. We also compare our infrared photometry with historical observations and revise the dust-formation period of WR 125 to 28.1 years. Archival infrared spectra of five dusty WC stars, WR 48a, WR 98a, WR 104, WR 112 and WR 118, obtained with ISO/SWS are reanalyzed and compared with the WR 125 spectrum to search for a similar feature. We analyze the dusty WC spectra using two different extinction curves to investigate the impact of interstellar extinction correction on the presence and/or properties of the 8 $\mu$m feature. All of the dusty WC spectra dereddened with the two different extinction curves show a broad feature around 8 $\mu$m (FWHM$\sim$1-2 $\mu$m). We suggest that these 8 $\mu$m features seen in the dusty WC spectra are related to the Class C unidentified infrared (UIR) features.