The Colliding Winds of WR 25 in High Resolution X-rays

TL;DR

This paper presents the first high-resolution X-ray spectral analysis of the colliding-wind binary WR 25, revealing how stellar wind interactions produce phase-dependent X-ray emission features.

Contribution

It provides detailed spectral measurements of WR 25's wind collision region using Chandra/HETGS, including line fluxes, centroids, and widths, and explores flux variation with orbital phase.

Findings

Line fluxes, centroids, and widths constrained for key emission lines.

Phase-dependent flux variation observed in off-axis spectra.

First high-resolution X-ray spectral study of WR 25.

Abstract

WR 25 is a colliding-wind binary star system comprised of a very massive O2.5If*/WN6 primary and an O-star secondary in a 208-day period eccentric orbit. These hot stars have strong, highly-supersonic winds which interact to form a bright X-ray source from wind-collision-shocks whose conditions change with stellar separation. Different views through the WR and O star winds are afforded with orbital phase as the stars move about their orbits, allowing for exploration of wind structure in ways not easy or even possible for single stars. We have analyzed an on-axis Chandra/HETGS spectrum of WR 25 obtained shortly before periastron when the X-rays emanating from the system are the brightest. From the on-axis observations, we constrain the line fluxes, centroids, and widths of various emission lines, including He-triplets of Si XIII and Mg XI. We have also been able to include several serendipitous off-axis HETG spectra from the archive and study their flux variation with phase. This is the first report on high-resolution spectral studies of WR 25 in X-rays.