Puzzling X-rays from the new colliding wind binary Wolf-Rayet 65 (WC9d)

L.M. Oskinova and W.-R. Hamann

Institut für Physik, Universität Potsdam, Germany

We report the discovery of variability in the X-ray emission from the Wolf-Rayet type star WR65. Using archival Chandra data spanning over 5yr, 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 in the different absorption column along the binary orbit. The X-ray spectra of WR65 display prominent emission features at wavelengths corresponding to the lines of strongly ionized Fe, Ca, Ar, S, Si and Mg. WR65 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 WR65.

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