Colliding Wind Binary Systems: Monte Carlo Simulations of Line-Profile Variability

Abstract

We investigate the line-profile variability observed in colliding wind binary systems. In these systems the ultraviolet P Cygni line profiles show marked orbital variability; the nature of which differs between individual lines and binaries. We present results of three-dimensional Monte Carlo simulations of the radiative transfer and line formation in colliding wind binaries. We present results for an idealized binary system, illustrating some of the factors that will affect line-profile formation in such systems, and the potential complexity of interpreting such variability. In addition, we calculate the expected line-profile variability for the archetypal W-R + O binary V444 Cyg. We compare these results with ultraviolet observations of this system, concentrating on the N IV 1718 A line. We find that our simplified model can account for many of the features of the observed variability of this line. We discuss the limitations of the model, but also stress the great potential for using such Monte Carlo techniques to analyze and determine the system and wind parameters of massive early-type binary systems.