A hydrodynamic study of the circumstellar envelope of α Scorpii

Context. Both the absolute mass-loss rates and the mechanisms that drive the mass loss of late-type supergiants are still not well known. Binaries such as alpha Sco provide the most detailed empirical information about the winds of these stars. Aims. Our goal was to improve the binary technique for the determination of the mass-loss rate of alpha Sco A by including a realistic density distribution and velocity field from hydrodynamic and plasma simulations. Methods. We performed 3D hydrodynamic simulations of the circumstellar envelope of alpha Sco in combination with plasma simulations accounting for the heating, ionization, and excitation of the wind by the radiation of alpha Sco B. These simulations served as the basis for an examination of circumstellar absorption lines in the spectrum of alpha Sco B as well as of emission lines from the Antares nebula. Results. The present model of the extended envelope of alpha Sco reproduces some of the structures that were observed in the circumstellar absorption lines in the spectrum of alpha Sco B. Our theoretical density and velocity distributions of the outflow deviate considerably from a spherically expanding model, which was used in previous studies. This results in a higher mass-loss rate of (2 +/- 0.5) x 10(-6) M-circle dot yr(-1). The hot H II region around the secondary star induces an additional acceleration of the wind at large distances from the primary, which is seen in absorption lines of Ti II and Cr II at -30 km s(-1).