Puzzling X-rays from the new colliding wind binary WR65

TL;DR

This study reports the discovery of variable X-ray emission from the Wolf-Rayet star WR 65, likely caused by wind-wind collision in a binary system, with spectral features indicating highly ionized elements and complex dust-related effects.

Contribution

First detailed X-ray spectral analysis of a WC9d Wolf-Rayet star, revealing variability and complex emission mechanisms related to binary wind interactions.

Findings

X-ray flux varies by a factor of 3 over 5 years

X-ray spectra show emission lines of highly ionized elements

Variability explained by changes in emission measure and absorption along orbit

Abstract

We report the discovery of variability in the X-ray emission from the Wolf-Rayet type star WR 65. Using archival Chandra data spanning over 5 yr we detect changes of the X-ray flux by a factor of 3 accompanied by changes in the X-ray spectra. We believe that this X-ray emission originates from wind-wind collision in a massive binary system. The observed changes can be explained by the variations in the emission measure of the hot plasma, and by the different absorption column along the binary orbit. The X-ray spectra of WR 65 display prominent emission features at wavelengths corresponding to the lines of strongly ionized Fe, Ca, Ar, S, Si, and Mg. WR 65 is a carbon rich WC9d star that is a persistent dust maker. This is the first investigation of any X-ray spectrum for a star of this spectral type. There are indications that the dust and the complex geometry of the colliding wind region are pivotal in explaining the X-ray properties of WR 65.