The CHARA Array resolves the long-period Wolf-Rayet binaries WR 137 and WR 138

TL;DR

This study uses the CHARA Array to resolve and analyze the binary components of two Wolf-Rayet stars, WR 137 and WR 138, providing new measurements of their separations, flux ratios, and fundamental parameters, and revealing insights into their binary nature and dust production.

Contribution

First interferometric resolution of WR 137 and WR 138 binaries, with detailed flux, separation, and fundamental parameter measurements, advancing understanding of their binary configurations and evolution.

Findings

WR 137 and WR 138 are resolved binaries with milliarcsecond separations.

WR stars dominate the H-band flux in both systems.

WR 138 likely experienced a mass-transfer episode; WR 137 is nearly edge-on.

Abstract

We report on interferometric observations with the CHARA Array of two classical Wolf-Rayet stars in suspected binary systems, namely WR 137 and WR 138. In both cases, we resolve the component stars to be separated by a few milliarcseconds. The data were collected in the H-band, and provide a measure of the fractional flux for both stars in each system. We find that the WR star is the dominant H-band light source in both systems ($f_{\rm WR, 137} = 0.59\pm0.04$; $f_{\rm WR, 138} = 0.67\pm0.01$), which is confirmed through both comparisons with estimated fundamental parameters for WR stars and O dwarfs, as well as through spectral modeling of each system. Our spectral modeling also provides fundamental parameters for the stars and winds in these systems. The results on WR 138 provide evidence that it is a binary system which may have gone through a previous mass-transfer episode to create the WR star. The separation and position of the stars in the WR 137 system together with previous results from the IOTA interferometer provides evidence that the binary is seen nearly edge-on. The possible edge-on orbit of WR 137 aligns well with the dust production site imaged by the Hubble Space Telescope during a previous periastron passage, showing that the dust production may be concentrated in the orbital plane.