Context. There is indirect evidence of non-conservative evolutions in Algols. However, the systemic mass-loss rate is poorly constrained by observations and generally set as a free parameter in binary-star evolution simulations. Moreover, systemic mass loss may lead to observational signatures that still need to be found. Aims. Within the "hotspot" ejection mechanism, some of the material that is initially transferred from the companion star via an accretion stream is expelled from the system due to the radiative energy released on the gainer's surface by the impacting material. The objective of this paper is to retrieve observable quantities from this process and to compare them with observations. Methods. We investigate the impact of the outflowing gas and the possible presence of dust grains on the spectral energy distribution (SED). We used the 1D plasma code Cloudy and compared the results with the 3D Monte-Carlo radiative transfer code Skirt for dusty simulations. The circumbinary mass-distribution and binary parameters were computed with state-of-the-art binary calculations done with the Binstar evolution code. Results. The outflowing material reduces the continuum flux level of the stellar SED in the optical and UV. Because of the timedependence of this effect, it may help to distinguish between different ejection mechanisms. If present, dust leads to observable infrared excesses, even with low dust-to-gas ratios, and traces the cold material at large distances from the star. By searching for this dust emission in the WISE catalogue, we found a small number of Algols showing infrared excesses, among which the two rather surprising objects SX Aur and CZ Vel. We find that some binary B[e] stars show the same strong Balmer continuum as we predict with our models. However, direct evidence of systemic mass loss is probably not observable in genuine Algols, since these systems no longer eject mass through the hotspot mechanism. Furthermore, owing to its high velocity, the outflowing material dissipates in a few hundred years. If hot enough, the hotspot may produce highly ionised species, such as Si iv, and observable characteristics that are typical of W Ser systems. Conclusions. If present, systemic mass loss leads to clear observational imprints. These signatures are not to be found in genuine Algols but in the closely related β Lyraes, W Serpentis stars, double periodic variables, symbiotic Algols, and binary B[e] stars. We emphasise the need for further observations of such objects where systemic mass loss is most likely to occur.

Aims. The Antares nebula is a peculiar emission nebula seen in numerous [Fe ii] lines and in radio free-free emission, probably associated with the H ii region caused by α Sco B in the wind of α Sco A. High-resolution spectra with spatial resolution were used to study the emission line spectrum, the physical nature of the nebula and to determine the mass-loss rate of the M supergiant α Sco A. Methods. The Antares nebula was mapped with long-slit (10 ) and high-resolution (R = 80 000) spectra using UVES at the VLT. The resulting 2-D images were used to reconstruct a 3-D picture of the H ii region and its absolute location in space relative to α Sco A. Results. We found that the Antares nebula shows, in addition to numerous [Fe ii] lines, the Balmer line recombination spectrum H α , H β up to H 10 , and [N ii] 6583/6548 Å, H α and [N ii] with the same extent as seen in cm radio free-free emission. Combining velocity information from optical and GHRS/HST spectra with H α velocities, the H ii region is found to be located ∼215 AU behind the plane of the sky of α Sco A. From the H α /[N ii] intensity ratio and the non-visibility of the [O ii] 3726/3729 Å lines we estimate a low mean electron temperature of T e = 4900 K and an N abundance enhanced by a factor of ∼3 due to the CNO cycle in α Sco A. The shape and size of the H ii region yield a mean mass-loss rate of (1.05 ± 0.3) × 10 −6 M yr −1 . The [Fe ii] lines originate predominantly at the edges (rear and front) of the H ii region. UV continuum pumping as well as collisional excitation seem to be responsible for the observed iron lines.

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 α 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 α 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 α Sco in combination with plasma simulations accounting for the heating, ionization, and excitation of the wind by the radiation of α Sco B. These simulations served as the basis for an examination of circumstellar absorption lines in the spectrum of α Sco B as well as of emission lines from the Antares nebula.Results. The present model of the extended envelope of α Sco reproduces some of the structures that were observed in the circumstellar absorption lines in the spectrum of α 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) × 10 −6 M 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 .