The long-period spectroscopic orbit and dust creation in the Wolf-Rayet binary system WR 125

TL;DR

This paper characterizes the long-period orbit and dust formation in the Wolf-Rayet binary WR 125, using infrared and optical data to derive orbital parameters and dust properties, enhancing understanding of dust production in such systems.

Contribution

It provides the first orbital constraints for WR 125, including period and eccentricity, and analyzes dust properties during an outburst, advancing knowledge of dust creation in Wolf-Rayet binaries.

Findings

Orbital period of 28.12 years with mild eccentricity of 0.29.

Infrared outburst consistent with dust formation near periastron.

Dust temperature estimated at 580 K during the outburst.

Abstract

Several long-period binaries with a carbon-rich Wolf-Rayet star and an O star produce dust in their wind collisions. In eccentric binaries, this is seen most strongly near periastron passage. The exact conditions leading to dust creation require orbital properties to be determined, which is difficult owing to their long periods. Recently, the binary system WR 125 (WC7+O9III) began a dust creation episode seen through an infrared outburst first detected by NEOWISE-R, which was the first outburst detected since 1991. We present new near- and mid-infrared photometry, which we use to show consistency between the two outbursts and derive an orbital period of 28.12$^{+0.10}_{-0.05}$ yr. We use a long time-series of optical spectra to place the first constraints on its orbital elements, on the assumption that this system will produce dust near periastron. The orbit has a mild eccentricity of 0.29$\pm$0.12 and is only derived for the Wolf-Rayet component, as the O star's radial velocities have noise that is likely larger than the expected semi-amplitude of the orbit. We also present SOFIA/FORCAST grism spectroscopy to examine the infrared spectral energy distribution (SED) of the dust during this outburst, comparing its properties to other WCd binaries, deriving a dust temperature of 580 K in 2021. This collection of observations will allow us to plan future observations of this system and place the system in the context of dust-creating Wolf-Rayet binaries.