Mass-loss rate determination for the massive binary V444 Cygni using 3-D Monte-Carlo simulations of line and polarization variability

¹ Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA
² Department of Physics & Astronomy, The University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK

Corresponding author: R. Kurosawa, kurosawa@phyast.pitt.edu

Received: 24 December 2001
Accepted: 22 March 2002

Abstract

A newly developed 3-D Monte Carlo model is used, in conjunction with a multi-line non-LTE radiative transfer model, to determine the mass-loss rate of the Wolf-Rayet (W-R) star in the massive binary V444 Cyg (WN5+O6). This independent estimate of mass-loss rate is attained by fitting the observed Å and Å line profiles, and the continuum light curves of three Stokes parameters in the band simultaneously. The high accuracy of our determination arises from the use of many observational constraints, and the sensitivity of the continuum polarization to the mass-loss rate. Our best fit model suggests that the mass-loss rate of the system is , and is independent of the assumed distance to V444 Cyg. The fits did not allow a unique value for the radius of the W-R star to be derived. The range of the volume filling factor for the W-R star atmosphere is estimated to be in the range of 0.050 (for ) to 0.075 (for ). We also found that the blue-side of Å and Å lines at phase 0.8 is relatively unaffected by the emission from the wind-wind interaction zone and the absorption by the O-star atmosphere; hence, the profiles at this phase are suitable for spectral line fittings using a spherical radiative transfer model.