Characterising the magnetic fields and accretion flows in the young SB2 binary system V380 Ori

Star and planet formation is an active field of research. Magnetospheric accretion is a key process in the evolution of the disk-(planet)-star system. This process channels material from the inner edge of the disk onto the star’s surface along the star’s magnetic field lines. The resulting impact on the star generates energetic and intense radiation. To understand these phenomena, we need to study the magnetic fields and accretion flows of young stars and model them. Our ODYSSey team at IPAG is highly active in this field and, until now, has primarily focused on studying single stars.

Most stars are not born alone but in binary systems. In the case of close binaries (separated by a few fractions of an astronomical unit), such as V380 Ori, we expect the accretion processes onto the stars to be altered. The magnetospheres of both stars may interact as they draw closer, increasing the energetic fluxes impacting the protoplanetary disk, hence planetary formation.

To date, very few studies have examined magnetic fields and accretion flows in binary systems. All existing studies have relied on photometric and spectropolarimetric data, but none have combined these with long-baseline optical interferometry, which can spatially resolve the innermost regions of these systems (< 1 astronomical unit). We have obtained a unique dataset for a young binary system, observed quasi-simultaneously with two spectropolarimeters, ESPaDOnS and SPIRou, and the GRAVITY interferometer. In this thesis, we propose to study the spectropolarimetric data of this system, V380 Ori. The analysis of ESPaDOnS and SPIRou data will allow us to characterize stellar and orbital properties of both stars (effective temperature, surface gravity, stellar rotation speeds, orbital period, and orbital eccentricity) and to map their magnetic fields. Subsequently, the study of accretion lines (He I at 1 micron, and hydrogen lines Pa Beta, Br Gamma), combined with the analysis of atomic lines formed at the star’s surface, will help us determine whether both stars are accreting and, if so, at what rate. This study will also reveal whether the accretion onto the stars is magnetospheric or occurs differently. In parallel, the analysis of GRAVITY interferometric data, led by K. Perraut, will enable us to fully characterize the binary’s orbit (particularly its inclination) and to constrain the geometry and extent of one or more disks (circumstellar or circumbinary), as well as the potential position of accretion flows relative to the stars. The observational constraints obtained can be compared with numerical simulations, in collaboration with N. Cuello from the ODYSSey team at IPAG.

This thesis will pave the way for more systematic analyses of binary systems that we are currently discovering or will discover through projects involving the ESPaDOnS and SPIRou instruments. Additionally, the new instrumentation at the Canada-France-Hawaii Telescope includes the installation of WENAOKEAO, an instrument that will allow simultaneous observations of a star with ESPaDOnS and SPIRou. The V380 Ori dataset to be studied during the thesis is the first to combine quasi-simultaneous observations from SPIRou and ESPaDOnS, covering a vast wavelength range from the near-UV to the near-IR. Covering such a large wavelength range enables a comprehensive study of the magnetosphere, extending from the star’s surface to the inner edge of the disk.