Modelling the spectrum of Mg in cool stars

The astrophysical importance of Mg, together with its unique range of spectral features in late-type stars, plus its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-local thermodynamic equilibrium (NLTE) modelling in stellar atmospheres. In this paper, we present example first results for calculations of NLTE Mg line based on a new model atom with significant improvements in the collision data for neutral Mg. We perform calculations for excitation of the lower-lying levels due to electron impacts using the R-matrix method. Recent data for excitation and charge transfer due to hydrogen atom impacts involving low-lying levels are now employed. Further, we have made efforts to use physically-motivated methods for calculating radiative and collisional data involving Rydberg states. The results are compared with observed spectra and the impact of the new calculations briefly explored