MESA ISOCHRONES and STELLAR TRACKS (MIST) 0: METHODS for the CONSTRUCTION of STELLAR ISOCHRONES

I describe a method to transform a set of stellar evolution tracks onto a uniform basis and then interpolate within that basis to construct stellar isochrones. This method accommodates a broad range of stellar types, from substellar objects to high-mass stars, and phases of evolution, from the pre-main sequence to the white dwarf cooling sequence. I discuss situations in which stellar physics leads to departures from the otherwise monotonic relation between initial stellar mass and lifetime, and how these may be dealt with in isochrone construction. I close with convergence tests and recommendations for the number of points in the uniform basis and the mass between tracks in the original grid required to achieve a certain level accuracy in the resulting isochrones. The programs that implement these methods are free and open-source; they may be obtained from the project webpage.