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When the winds of two massive stars orbiting each other collide, an interaction zone is created consisting of two shock fronts at both sides of a contact surface. During the cooling process, elements may recombine generating spectral lines. These lines may be Doppler shifted, as the gas stream flows over the interaction zone. To calculate the stream velocity projected into the line of sight we use a simplified conical geometry for the shock fronts and, to determine the synthetic line profile, we have to sum the amount of emitting gas elements with the same Doppler shifted velocity. We show that the stellar mass loss rates and wind velocities, and the orbital inclination and eccentricity, are the main parameters on this physical process. By comparing observational data to the synthetic line profiles it is possible to determine these parameters. We tested this process to Brey 22 WR binary system, and applied to the enigmatic object of η Carinae. [ABSTRACT FROM PUBLISHER]

The study of Wolf–Rayet stars plays an important role in evolutionary theories of massive stars. Among these objects, ∼20 per cent are known to be in binary systems and can therefore be used for the mass determination of these stars. Most of these systems are not spatially resolved and spectral lines can be used to constrain the orbital parameters. However, part of the emission may originate in the interaction zone between the stellar winds, modifying the line profiles and thus challenging us to use different models to interpret them. In this work, we analysed the He iiλ4686 Å+ C ivλ4658 Å blended lines of WR 30a (WO4+O5) assuming that part of the emission originate in the wind–wind interaction zone. In fact, this line presents a quiescent base profile, attributed to the WO wind, and a superposed excess, which varies with the orbital phase along the 4.6-d period. Under these assumptions, we were able to fit the excess spectral line profile and central velocity for all phases, except for the longest wavelengths, where a spectral line with constant velocity seems to be present. The fit parameters provide the eccentricity and inclination of the binary orbit, from which it is possible to constrain the stellar masses. [ABSTRACT FROM AUTHOR]

One of the most intriguing spectral features of Wolf–Rayet (WR) binary stars is the presence of time-dependent line profiles. Long-term observations of several systems revealed the periodicity of this variability, synchronized with the orbital movement. Several partially successful models have been proposed to reproduce the observed data. The most promising model assumes that the origin of the emission is the wind–wind interaction zone. In this scenario, two high velocity and dense winds produce a strong shock layer, responsible for most of the X-rays observed from these systems. As the gas cools down, flowing along the interaction surface, it reaches recombination temperatures and generates the emission lines. Luhrs noted that, as the secondary star moves along its orbital path, the shock region, of conical shape, changes its position with relation to the line of sight. As a consequence, the stream-measured Doppler shift presents time variations resulting in position changes of the spectral line. However, his model requires a very thick contact layer and also fails to reproduce recently observed line profiles of several other WR binary systems. In our work, we present an alternative model, introducing turbulence in the shock layer to account for the line broadening and opacity effects for the asymetry in the line profiles. We showed that the gas turbulence avoids the need of an unnaturally large contact layer thickness to reproduce line broadening. Also, we demonstrated that if the post-shock gas is optically thick at the observed line frequency, the emission from the opposing cone surface is absorbed, resulting in a single-peaked profile. This result fully satisfies the recent data obtained from massive binary systems, and can help in the determination of both the winds and the orbital parameters. We successfully applied this model to the Br22 system and determined its orbital parameters. [ABSTRACT FROM AUTHOR]

In this paper we use the 7- and 1.3-mm light curves obtained during the 2003.5 low-excitation phase of the η Carinae system to constrain the possible parameters of the binary orbit. To do that we assumed that the millimetre-wave emission is produced in a dense disc surrounding the binary system; during the low-excitation phase, which occurs close to periastron, the number of ionizing photons decreases, producing the dip in the radio emission. On the other hand, due to the large eccentricity, the density of the shock region at periastron is very high and the plasma is optically thick for free–free radiation at 7 mm, explaining the sharp peak that was observed at this frequency and lasted for about 10 d. From the shape and duration of the peak we were able to determine the orbital parameters of the binary system, independently of the stellar parameters, such as mass-loss rates, wind velocities or temperature at the post-shock region. [ABSTRACT FROM AUTHOR]

The exact nature ofη Carinae is still an open issue. Strict periodicity in the light curves at several wavelengths seem to point to a binary system, but the observed radial velocities, measured from space with high spatial resolution, are in conflict with the ground-based observations used to calculate the binary orbit. Also, the observed 2–10 keV X-ray flux is much larger that what is expected from a single star, and favours the wind–wind collision hypothesis, characteristic of high-mass binary systems. However, to explain the duration of the dip in the light curve by wind collisions, it is necessary to postulate a very large increase in theη Carinae mass loss rate. Finally, the optical and ultraviolet light curves are better explained by periodic shell-ejection events. In this paper we conciliate the two hypotheses. We still assume a binary system to explain the strong X-ray emission, but we also take into account that, near periastron and because of the highly eccentric orbit, the wind emerging fromη Carinae accumulates behind the shock and can mimic a shell-like ejection event. For this process to be effective, at periastron the secondary star should be located betweenη Carinae and the observer, solving also the discrepancy between the orbital parameters derived from ground- and space-based observations. We show that, as the secondary moves in its orbit, the shell cools down and the number of available stellar ionizing photons is not enough to maintain the shell temperature at its equilibrium value of about 7500 K. The central part of the shell remains cold and under these conditions grain formation and growth can take place in time-scales of hours. We also calculated the neutral gas column density intercepting the line of sight at each point of the orbit near periastron, and were able to reproduce the form and duration of the X-ray light curve without any change in theη Carinae mass loss rate. This same column density can explain the observed Hα light curve observed during the 2003 event. [ABSTRACT FROM AUTHOR]