MESA Isochrones and Stellar Tracks. II. Models with alpha-enhanced chemical composition

Abstract: We update and expand the MESA Isochrones and Stellar Tracks (MIST) database to include variations in the alpha-capture elements, specifically [alpha/Fe]=-0.2, 0, +0.2, +0.4, and +0.6 for -3 <= [Fe/H] <= +0.5. Variations in [alpha/Fe] are included in a self-consistent manner from the stellar interior models to the synthetic spectra used to translate these models in the observational plane. We describe a number of updates to the physics utilized in these models as well as new information provided by the models. We validate the models with comparisons to other stellar evolution models including the previous generation of MIST and other models from the literature. MIST data products including stellar evolutiont tracks, isochrones, and bolometric correction tables can be obtained from the MIST project website, https://mist.science. All necessary files to reproduce MIST models are available from Zenodo.