XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1

¹ Department of Astronomy, University of Wisconsin, Madison, WI 53706, USA
² Astrophysik, Univerität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
³ Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK

Corresponding author: R. Ignace, ignace@astro.wisc.edu

Received: 14 May 2003
Accepted: 27 June 2003

Abstract

We present XMM-Newton results for the X-ray spectrum from the N-rich Wolf-Rayet (WR) star WR 1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: (a) significant emission “bumps” appear that are coincident with the wavelengths of typical strong lines, such as Mgxi, Si xiii, and Sxv; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and (c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X-rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone (in contrast to colliding wind zones). Although the properties of the S-edge are not well-constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge.