The ultraviolet morphology of evolved populations

In this paper I present a summary of the recent investigations we have developed at the Stellar Atmospheres and Populations Research Group (GrAPEs-for its designation in Spanish) at INAOE and collaborators in Italy. These investigations have aimed at providing updated stellar tools for the analysis of the UV spectra of a variety of stellar aggregates, mainly evolved ones. The sequence of material here presented roughly corresponds to the steps we have identified as mandatory to properly establish the applicability of synthetic populations in the analyses of observational data of globular clusters and more complex aged aggregates. The sequence is composed of four main stages, namely, (a) the creation of a theoretical stellar data base that we have called UVBLUE, (b) the comparison of such data base with observational stellar data, (c) the calculation of a set of synthetic spectral energy distributions (SEDs) of simple stellar populations (SSPs) and their validation through a comparison with observations of a sample of galactic globular clusters (GGCs), (d) construction of models for dating local ellipticals and distant red-envelope galaxies. Most of the work relies on the analysis of absorption line spectroscopic indices. The global results are more than satisfactory in the sense that theoretical indices closely follow the overall trends with chemical composition depicted by their empirical counterparts (stars and GGCs).