Line profile variations in WR+O binary systems

I. The code and basic predictions

¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, México e-mail: georgiev@astroscu.unam.mx
² Centro de Ciencias Físicas, Universidad Nacional Autónoma de México, México e-mail: gloria@astroscu.unam.mx

Received: 7 January 2003
Accepted: 13 January 2004

Abstract

We compute the P Cyg line profiles formed by the stellar winds of binary systems containing a Wolf-Rayet and an O-type star, incorporating the effects due to wind eclipses and wind-wind collisions. The contribution from both stellar winds to the P Cygni emission lines is modeled for different orbital phases. The opacity and the source function are calculated assuming a simplified atom and the Sobolev approximation, and the emission-line profile is calculated by exact radiative transfer through the 3D geometry wind. We analyze the cases of a P Cygni line that is formed only in the WR wind, and the case of a line formed in both the WR and the O-star winds. The line-profile variations that are predicted by this model are presented. When compared with observations, the synthetic profiles and their phase-dependent variability provide an estimate for the opening angle of the WWC shock cone and the velocity law of both stellar winds. Ultraviolet (UV) observations of the binary system  Vel are used to illustrate how the model predictions can be applied to the observational data.