Search for the signatures of mass-exchange episodes in massive binaries

Massive stars are known for their crucial role in our Universe, through their extreme stellar parameters, leading to a strong impact on their environment. However, there remain numbers of unanswered questions concerning the exact processes of their formation, their stability or the processes driving their strong stellar winds. In the context of this thesis work, we adress one of the most interesting of their peculiarities: their tendency to be part of binary of higher multiplicity systems. Whilst this multiplicity does help to solve some open issues by allowing us to study some of the fundamental properties of the stars, such as their minimum masses and radii as well as their stellar luminosities, it can also lead to interactions between the components of a system, which affect the subsequent evolution of the stars and give rise to additional open questions on the processes in place in such systems. Among the possible interactions taking place within close binary systems is the possibility of a transfer of mass and kinetic momentum through a Roche lobe overflow. This process has a huge impact on the subsequent evolution of both components and many aspects of this phenomenon are not well understood yet.

The present work is devoted to the search for the signatures of such past mass-exchange episodes in a sample of four short-period massive multiple systems: HD 149404, LSS 3074, HD 17505 and HD 206267. We determined a new orbital solution for three of them. We then used phase-resolved spectroscopy to perform the spectral disentangling of the optical spectra of the components. The spectral disentangling is a mathematical tool which allows to separate the contributions of both components to the observed spectra of a system. We then analysed the reconstructed spectra with the CMFGEN atmosphere code to determine stellar parameters, such as the effective temperatures and surface gravities, and to constrain the surface chemical composition of each component.

The first two parts of this dissertation are dedicated to the scientific background and the description of the numerical tools and methods used in this work. The third part presents our studies of the selected massive systems. We confirmed that the hypothesis of a past Roche lobe overflow episode is most plausible to explain the observed properties of the components of HD 149404. Photometric data permitted us to confirm that LSS 3074 is in an overcontact configuration, and a combined analysis with spectroscopy showed that the system has lost a significant fraction of its mass to its surroundings. We proposed several possible evolutionary pathways involving a Roche lobe overflow process to explain the current parameters of its components. We found no evidence of past mass-transfer episodes in the spectra of HD 17505 and showed that the current properties of its components can be explained by single star evolutionary models including rotational mixing. We found clues of binary interactions in the spectra of HD 206267, but suggested that the system did not experience a complete Roche lobe overflow episode at this stage of its evolution.