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Red supergiants are massive evolved stars that contribute extensively to thechemical enrichment of our Galaxy. It has been shown that convection in thosestars gives rise to large granules that cause surface inhomogeneities and shockwaves in the photosphere. The understanding of their dynamics is crucial tounveil the unknown mass-loss mechanism, their chemical composition and stellarparameters. We present a new generation of red supergiants simulations with amore sophisticated opacity treatment done with 3D radiative- hydrodynamicsCO5BOLD. In the code, the coupled equations of compressible hydrodynamics andnon-local radiation transport are solved in the presence of a sphericalpotential. The stellar core is replaced by a special spherical inner boundarycondition, where the gravitational potential is smoothed and the energyproduction by fusion is mimicked by a simply producing heat corresponding tothe stellar luminosity. The post-processing radiative transfer code OPTIM3D isused to extract spectroscopic and interferometric observables. We show that therelaxation of the assumption of frequency-independent opacities shows a steepermean thermal gradient in the optical thin region that affect strongly theatomic strengths and the spectral energy distribution. Moreover, the weakertemperature fluctuations reduce the incertitude on the radius determinationwith interferometry. We show that 1D models of red supergiants must include aturbulent velocity calibrated on 3D simulations to obtain the effective surfacegravity that mimic the effect of turbulent pressure on the stellar atmosphere.We provide an empirical calibration of the ad-hoc micro- and macroturbulenceparameters for 1D models using the 3D simulations: we find that there is not aclear distinction between the different macroturbulent profiles needed in 1Dmodels to fit 3D synthetic lines.

Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities