Numerical simulations of solar and stellar convection and oscillations

The Sun has a resonant cavity between the surface where the density decreases rapidly due to its low temperature and the interior where the sound speed increases with increasing temperature. Sound waves are trapped in this resonant cavity, and thousands of these p-mode oscillations are observed in the velocity Doppler shift and intensity variations of the lines in the solar spectrum. These resonant modes are excited by convection near the solar surface and are used to probe both the local and global structure of the Sun.; The question of interest here is excitation of acoustic waves by convection, and the interaction between convection and the resonant p-modes. Turbulent motions stochastically excite the resonant modes via Reynolds stresses and entropy fluctuations. Interaction between the convective motions and the waves modifies the mode frequencies, spectrum and amplitudes.; We investigate turbulence and its interaction with oscillations by means of the realistic three-dimensional numerical simulations of the shallow upper layer of the solar convective zone. We use the numerical code of Stein & Nordlund, which solves 3D system of the compressible (magneto) hydrodynamic equations and includes LTE radiative transfer near the visible surface.; The properties of oscillation modes in the simulation closely match their observed characteristics. This means that our numerical model reproduces the basic properties of solar oscillations. This is an important step in studying the physical properties of solar oscillations and their interaction with turbulence. The similarity of the oscillation mode properties in the simulation and observations means that the simulations can be used to investigate the origin of mode behavior and its interaction with turbulent plasma.; The frequency spectra of the solar acoustic modes are asymmetric. We study the corresponding asymmetry of the simulation modes in order to understand its origin and its relation to the excitation sources. We find that radiative transfer on top of the convection zone can be responsible for the acoustic mode asymmetry reversal.; Acoustic mode excitation rates depend on the details of the turbulent energy spectra. We analyze spatial and temporal components of the spectra in the simulations to learn more about stellar turbulent convection and its role in mode driving. We use similar simulations of convection in other stars to calculate their mode excitation rates, and determine how p-mode driving depends on stellar parameters.