The Wind‐Wind Collision Region of the Wolf‐Rayet Binary V444 Cygni: How Much Optical Line Emission Does It Produce?

Abstract

We model the emission-line proÐle variations that are expected to be produced by physical and wind eclipses in the Wolf-Rayet (W-R ] O) binary system V444 Cyg. A comparison of the theoretical proÐles with the He II 4686 line observed in V444 Cyg allows us to isolate the e †ects that are likely to be due A Ž to the wind-wind collision region in this particular line. We estimate that the wind-wind collision region contributes no more than D12% of the equivalent width of the emission line, with smaller values during elongations, when part of the shock cone is being eclipsed by the O star. The upper limit implies a maximum contribution from the wind-wind collision region of D1 ] 1035 ergs s~1 to the total lumi-nosity of He II 4686 line. Using the analytical solution of et al., we Ðnd that the bulk of this A Ž Canto emission arises along the shock cone walls where the Ñow velocity is D800 km s~1, at a distance of D8 from the O starÏs surface, and at h \ 65¡È75¡ from the line joining the centers of the two stars, with R _ origin in the O star. The derived surface density of this region is p \ 0.22 g cm~2, which, together with the He II 4686 luminosity, indicates that the thickness of the shock lies in the range 2È10 ] 1010 cm A Ž and the total density is 1È6 ] 1012 cm~3.