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Mg is the alpha element of choice for Galactic population and chemicalevolution studies as it is easily detectable in all late-type stars. Suchstudies require precise elemental abundances, and thus departures from LTE needto be accounted for. Our goal is to provide reliable departure coefficients andequivalent widths in non-LTE, and for reference in LTE, for diagnostic lines ofMg studied in late-type stars. These can be used e.g., to correct LTE spectraand abundances. Using the model atom built and tested in the preceding paper inthis series, we performed non-LTE radiative transfer calculations in a grid of3945 stellar 1D atmospheric models. We used a sub-grid of 86 models to explorethe propagation of errors in the recent atomic collision calculations to theradiative transfer results. We obtained departure coefficients for all thelevels and equivalent widths (in LTE and non-LTE) for all the radiativetransitions included in the "final" model atom of Osorio et al.. We present anddescribe our results and show some examples of applications of the data. Theerrors due to uncertainties in the collisional data are investigated andtabulated. The results for equivalent widths and departure coefficients aremade freely available. Giants tend to have negative abundance corrections whiledwarfs have positive, though small, corrections. Error analysis results showthat uncertainties related to the atomic collision data are typically of order0.01 dex or less, although for few stellar models in specific linesuncertainties can be as large as 0.03 dex. As these errors are less than or ofthe same order as typical corrections, we expect that we can use these resultsto extract Mg abundances from high quality spectra more reliably than fromclassical LTE analysis.

Mg line formation in late-type stellar atmospheres: II. Calculations in a grid of 1D models