Abstract
Thanks to their high-peak infrared luminosity, red supergiant (RSG) stars are fundamental tracers of galactic structure, efficiently probing regions of high interstellar extinction. To understand their properties is crucial and impacts a broad segment of Astrophysics.<br />In this thesis, the answer to the principal questions about RSGs is addressed with three-dimensional radiation hydrodynamic (RHD) models. The computer code CO5BOLD, developed by Freytag, Steffen, Ludwig and collaborators, is used. <br />First, I have developed a three-dimensional radiative transfer code that computes spectra and intensity maps from RHD simulations. With this tool at hand, I characterize the granulation pattern of the RHD models at different wavelengths and I study the impact of the convection on spectral line in term of line shifts and asymmetries, prospecting line bisectors and photocenter variations for future observations.<br />Then, I measure the characteristic atmospheric velocities. From the comparison with the observations I find that the simulations are in agreement with the observations even if the velocity amplitudes are smaller than what is observed.<br />Furthermore, the convection-related surface structures show an evident departure from the circular symmetry on the visibility curves and closure phases. I seek constraints of the atmospheric movements analysing these observables and I show where and how the convection pattern can be detected and measured. I conclude that today interferometers are the best way for the characterization of the convection on RSG strars.<br />Finally, I highlight that the principal problem of RHD simulations is the grey treatment of opacities and I explore the effects on the observables using a first non-grey testing model.