ProGeny I: a new simple stellar population spectra generator and impact of isochrones / stellar atmospheres / initial mass functions

In this work we introduce ProGeny, a new stellar population library (SPL) software package written in R. This release encapsulates the core software (github.com/asgr/ProGeny) to generate simple/single stellar populations and their associated spectra (SSPs); the various data inputs required (in particular isochrones and stellar atmospheres); example scripts to generate the SSPs; and a number of pre-generated static SSP available for immediate use. The most novel feature of ProGeny is its ability to produce SSPs with evolving initial mass functions, allowing functional dependencies on stellar age or metallicity. We perform both internal comparisons (within the ProGeny SPL) and external comparisons (with other public SSPs) and tests. The main conclusion is that the choice of isochrone has significantly more impact on the predicted spectra than the choice of stellar atmospheres and/or IMF (comparing Chabrier and Kroupa variants). A number of limiting uncertainties and corrections for star formation rates and stellar masses are also presented.