Carbon-rich dust injected into the interstellar medium by Galactic WC binaries survives for hundreds of years

TL;DR

This study uses JWST imaging to show that dust produced by Galactic WC binaries survives for over a century, influencing the interstellar medium and contributing significantly to galactic dust budgets.

Contribution

First direct imaging evidence of long-lived dust shells around WC binaries, revealing dust survival times and structures, with implications for galactic dust modeling.

Findings

Dust shells are at least 130 years old, some over 300 years.

Dust propagates at speeds comparable to stellar wind velocities.

Unusual structures around WR 48a suggest dusty clumps shaped by photoevaporation.

Abstract

Some carbon-rich Wolf-Rayet stars (WC stars) show an infrared excess from dust emission. Dust forms in the collision of the WC wind with a companion star's wind. As this dust is carried towards the ISM at close to the WCd wind speed and the binary continues through its orbit, a spiral structure forms around the system. The shape depends on the orbital eccentricity and period, as well as stellar parameters like mass-loss rates and terminal wind speeds. Imaging of the WCd binary WR 140 with JWST/MIRI revealed 17 concentric dust shells surrounding the binary. We present new JWST imaging of four additional WCd systems (WR 48a, WR 112, WR 125, and WR 137) that were imaged in 2024. In this analysis, we show that the dust is long-lived, detected with an age of at least 130 years, but more than 300 years in some systems. Longer duration measurements are limited by sensitivity. Regular spacing of dust features confirms the periodic nature of dust formation, consistent with a connection to binary motion. We use these images to estimate the proper motion of the dust, finding the dust to propagate out to the interstellar medium with motion comparable to the wind speed of the WC stars. In addition to these results, we observe unusual structures around WR 48a, which could represent dusty clumps shaped by photoevaporation and wind ablation like young proplyd objects. These results demonstrate that WC dust is indeed long-lived and should be accounted for in galactic dust budgets.