Stellar Wind Accretion and Dynamics in Binary Stars and Exoplanetary Systems

This thesis work is concerned with the accretion processes and flow structures associated with stellar winds in binary systems. I study mass transfer via stellar wind capture in symbiotic recurrent nova RS Ophiuchi, using Smoothed Particle Hydrodynamics. I investigate the modes of mass transfer from the mass-losing star to the mass-accreting companion by implementing wind expansion based on the analytical Parker solution for isothermal winds. Mass capture fractions are calculated and found to be dependent on the velocity of the wind. The structure of the accretion discs formed is also investigated. The results show that all the accretion discs have radial extents larger than the predicted stability radius against thermal viscous instabilities. It is nevertheless found that the surface density profiles of the accretion discs are too low to trigger such disc outbursts. I also explore the effect of rotation on mass transfer and disc morphology. I also study the interaction between the transiting hot Jupiter WASP-12b and its host star, using ZEUS-2D and SPH-3D to simulate the planetary magnetosphere interactions with the stellar wind self-consistently. I attempt to model NUV absorption due to enhancements in density at the bow shock ahead of the planet. The numerical results show that the bow shock is always weak and broad due to the modest wind Mach number at the planetary distance. I compute theoretical UV light-curves from the hydrodynamic models and use a grid of stellar wind, planetary magnetic field strength and wind opacity parameters to show how the UV light-curves depend on different physical model parameters. The results show consistency with the existing UV data for WASP-12b. I also model two other transiting hot Jupiters and show that additional UV observations of more massive short-orbit hot Jupiters should distinguish clearly between different models for circumplanetary absorption.