A Multi-wavelength Study to Investigate Different Emission Mechanisms Triggered by Binarity and Magnetism in Massive Stars

Abstract

Massive stars with magnetic fields and binary companions experience complex evolutionary pathways. Magnetic confinement of stellar winds alters mass-loss rates and rotation, potentially influencing compact-object formation, while binarity introduces tidal forces, mass transfer, and wind collisions. Although large-scale magnetic fields are detected in about 10% of isolated hot stars, they are rarer in close binaries, suggesting a link between magnetic field evolution and binary survival. Magnetic stars host structured magnetospheres that emit across the electromagnetic spectrum; in binaries, additional processes such as wind collisions and magnetospheric interactions further shape these emissions. Despite advances in separate studies of magnetism and binarity, their combined impact remains poorly understood. This thesis investigates their interaction using a coordinated, multi-wavelength observational approach. I conducted systematic observational campaigns targeting magnetic massive stars in both single and binary systems. A low-frequency radio survey of single magnetic stars was performed to establish baseline emission properties and their dependence on stellar parameters. A complementary pilot survey of magnetic binaries employed multi-epoch radio observations to probe variability across orbital phases and identify binarity-driven signatures. In parallel, detailed multi-wavelength follow-up studies were carried out on selected magnetic binaries spanning diverse stellar and orbital configurations, including doubly-magnetic systems, short- and long-period binaries, synchronized stars, and post-merger systems. Several key discoveries emerged. Orbitally modulated radio and X-ray emissions were detected in the doubly-magnetic system eps Lupi, providing the first direct evidence of magnetospheric interaction between two massive stars. The rapidly rotating star HR 5907 displayed extraordinary low-frequency radio emission consistent with auroral processes. High-resolution X-ray spectroscopy of Plaskett’s star revealed both orbital and rotational modulation, enabling detailed magnetospheric mapping. In the post-merger system HD 148937, multi-frequency radio observations highlighted wind-wind interactions as a driver of orbital variability. Together, these studies contribute to a more comprehensive understanding of the physical processes arising from the interaction of magnetic fields and binarity in massive stars. The findings underscore the importance of a multi-wavelength observational framework to capture the full complexity of emission mechanisms and to assess their implications for the evolution of massive stars.