Detection of a Broad 8 μm UIR Feature in the Mid-infrared Spectrum of WR 125 Observed with Subaru/COMICS

Abstract

Abstract We present the detection of a broad 8 μm feature in newly formed dust around the carbon-rich Wolf-Rayet (WC) binary WR 125 from N-band low-resolution (NL; R ∼ 250) spectroscopy between 7.3 and 13.6 μm and N-band (11.7 μm) and Q-band (18.8 μm) imaging with Subaru/COMICS in 2019 October. WR 125 is a colliding-wind binary (WC7 + O9) that exhibited renewed dust formation starting in 2018, ∼28 yr 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 yr. Archival infrared spectra of five dusty WC stars, WR 48a, WR 98a, WR 104, WR 112, and WR 118, obtained with Infrared Space Observatory/Short-Wavelength Spectrometer 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 μm feature. All of the dusty WC spectra dereddened with the two different extinction curves show a broad feature around 8 μm (FWHM ∼ 1–2 μm). We suggest that these 8 μm features seen in the dusty WC spectra are related to the Class C unidentified infrared features.