Revealing Efficient Dust-Formation at Low Metallicity in Extragalactic Carbon-Rich Wolf-Rayet Binaries

Abstract

We present Spitzer/IRAC observations of dust formation from six extragalactic carbon-rich Wolf-Rayet (WC) binary candidates in low-metallicity (Z $\lesssim 0.65$ Z${}_{\odot }$) environments using multi-epoch mid-infrared (IR) imaging data from the SPitzer InfraRed Intensive Transients Survey (SPIRITS). Optical follow-up spectroscopy of SPIRITS~16ln, 19q, 16df, 18hb, and 14apu reveals emission features from C IV $\lambda 5801\text{-}12$~and/or the C III-IV $\lambda 4650$ He II $\lambda 4686$~blend that are consistent with early-type WC stars. We identify SPIRITS~16ln as the variable mid-IR counterpart of the recently discovered colliding-wind WC4+O binary candidate, N604-WRXc, located in the sub-solar metallicity NGC 604 H II~region in M33. We interpret the mid-IR variability from SPIRITS~16ln as a dust-formation episode in an eccentric colliding-wind WC binary. SPIRITS~19q, 16df, 14apu, and 18hb exhibit absolute [3.6] magnitudes exceeding one of most IR-luminous dust-forming WC systems known, WR~104 (M${}_{[3.6]}\lesssim -12.3$). An analysis of dust formation in the mid-IR outburst from SPIRITS~19q reveals a high dust production rate of ${\dot{M}}_d\gtrsim 2\times 10^{-6}$ M${}_{\odot }$ yr${}^{-1}$, which may therefore exceed that of the most efficient dust-forming WC systems known. We demonstrate that efficient dust-formation is feasible from early-type WC binaries in the theoretical framework of colliding-wind binary dust formation if the systems host an O-type companion with a high mass-loss rate ($\dot{M}\gtrsim 1.6\times 10^{-6}$ M${}_{\odot }$ yr${}^{-1}$). This efficient dust-formation from early-type WC binaries highlights their potential role as significant sources of dust in low-metallicity environments.

28 pages, 10 Figures, and 5 Tables. Accepted to ApJ on 2021 Jan 4 (Replacement of version submitted to arXiv on 2020 Nov 19)

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Cited by in corpus (5)

• Accurate dust temperature determination in a $z=7.13$ galaxy
• Nested Dust Shells around the Wolf-Rayet Binary WR 140 observed with JWST
• Smoke on the wind: dust nucleation in archetype colliding wind pinwheel WR104
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