Letter to the Editor

The dominant X-ray wind in massive star binaries

¹ Department of Physics & Astronomy, The University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
² Department of Physics & Astronomy, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

Corresponding author: J. M. Pittard, jmp@ast.leeds.ac.uk

Received: 8 March 2002
Accepted: 12 April 2002

Abstract

We investigate which shocked wind is responsible for the majority of the X-ray emission in colliding wind binaries, an issue where there is some confusion in the literature, and which we show is more complicated than has been assumed. We find that where both winds rapidly cool (typically close binaries), the ratio of the wind speeds is often more important than the momentum ratio, because it controls the energy flux ratio, and the faster wind is generally the dominant emitter. When both winds are largely adiabatic (typically long-period binaries), the slower and denser wind will cool faster and the stronger wind generally dominates the X-ray luminosity.