Simulations multicomposantes de jets et de leurs disques

Jets are outflows of matter originating from astrophysical objects with vastly different scales. They are observed around active galactic nuclei (AGN), compact objects, and young stars. These celestial bodies all share a common feature: an accretion disk. To explain collimated jets, certain models, namely the one proposed by Blandford & Payne (1982), rely on the presence of large-scale magnetic fields in the disk. These fields assist in both ejecting and confining the jets. However, accretion disks are not the only sources of outflows, and thus cannot fully explain the entirety of the observed jets.In this thesis, we focus on the composition of jets from young stars. We start by constructing a multicomponent framework that integrates both stellar winds and disk winds. To achieve this, semi-analytical solutions for the two components were combined. For the temporal evolution of these outflows, I used the MHD code PLUTO to run non-relativistic simulations on 2D axisymmetric grids (2.5D). In other words, physical quantities evolve over time, accounting for the toroidal components of the magnetic field and velocity. However, these fields remain static over time.Once a stable configuration was established, a distinction was introduced between the stellar atmosphere and the disk atmosphere, with separate heating expressions for each. This additional parameterization allowed for more refined control over the input variables. The study revealed that, for the simulated jets to match observations, it is necessary to reduce the heating compared to what is predicted by analytical solutions. Consequently, the temperatures required to produce jets consistent with observations do not need to exceed ~10⁶ K, even when the stellar wind is driven by a pressure gradient. The simulations also produced standing shocks along the jet’s rotational axis at distances close to the central object. These shocks align with UV observations of RY Tau, likely due to the presence of a physical stellar jet that achieves the correct balance of radial forces.In the final part of this thesis, I present the results of simulations for complete systems, where the inner region of the accretion disk was included. We introduced turbulent magnetic diffusivity via the Shakura-Sunyaev alpha parameter. Overall, the system is turbulent, and cyclic accretion was observed. We observe a cycle per year. RY Tau may also exhibit cyclic behavior, as observations show alternating quiescent and active phases. However, the duration of this phenomenon is still unknown. To determine whether the cycles observed in our simulations correspond to the transition period between quiescent and active phases of RY Tau, longer-term observations are required.