FORCASTing the spectroscopic dust properties of the WC+O binary WR137 with SOFIA

TL;DR

This study uses SOFIA mid-infrared spectra to analyze dust formation and wind interactions in the WC+O binary WR 137, revealing spectral feature shifts and potential wind-disk mixing effects.

Contribution

First mid-infrared spectroscopic analysis of WR 137 with SOFIA, identifying spectral feature evolution linked to dust formation and wind interactions in the binary system.

Findings

Detected shifting emission features around 6.3-6.4 μm over time.

Observed correlation between dust continuum growth and spectral feature changes.

Suggested wind-disk mixing influences dust formation in WR 137.

Abstract

WR 137 (HD 192641) is a binary system consisting of a carbon-rich Wolf-Rayet star and an Oe companion star in a 13-year orbit. Near periastron, the winds of the two stars collide and form carbonaceous dust. We obtained three mid-infrared grism spectra of the system with SOFIA and FORCAST during the last year of SOFIA's operations in July 2021, February 2021, and May 2022 (Cycle 9). Within these spectra, we have identified several wind lines from He I, He II, C III, and C IV that are emitted from the Wolf-Rayet wind as well as a weak emission feature around 6.3-6.4 $\mu$m that may have shifted its peak flux from 6.29 to 6.41$\mu$m through this time period. The weak feature grew as the continuum dust emission grew while the WR emission appeared to decline due to lower contrast with the continuum. Furthermore, we observe that the peak of the feature shifts to redder wavelengths during the observations. We compare this feature to the UIR feature and other emission lines identified in dusty WC binaries. For WR 137, we speculate that mixing of the winds in the system with the Oe star's disk is important for starting the dust formation and that it is less important as dust formation continues. Previous infrared photometry shows "mini-eruptions" of dust production which could then be explained with variations of the Oe star disk.