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Solving the TP-AGB STAR Conundrum: a KEY to Galaxy Evolution

Final Report Summary - STARKEY (Solving the TP-AGB STAR Conundrum: a KEY to Galaxy Evolution)

VII. Before dying as compact white dwarfs, all stars with initial masses up to 8 times the mass of the Sun evolve through the Thermally Pulsing Asymptotic Giant Branch, a very short but intense evolutionary phase characterized by an extraordinary richness of physical processes that include a unique nucleosynthesis and mixing episodes, radial pulsation, dust condensation and growth, mass loss. These complex processes produce peculiar features that are identifiable in spectro-photometric studies of resolved stellar populations, and affect the integrated properties of unresolved galaxies up to high redshift. In the last decade it has become evident how the uncertainties intrinsic to population synthesis models, and especially those related to the TP AGB contribution, often dominate over the observational errors when deriving galaxy properties (e.g.masses and ages) across cosmic times. The project solved this persistent condition of controversy and uncertainty, the so-called AGB conundrum, by adopting a global calibration method. First, we developed theoretical modular tool that interconnected all key aspects of the TP-AGB phase (stellar evolution, pulsation, dynamical atmosphere,dust formation, mass loss, radiative transfer). Once assembled, the theoretical machinery was linked with high quality observations of resolved TP-AGB stars in galaxies. This allowed us to characterize quantitatively the efficiency of major processes that affect the evolution of these dying stars, chemical mixing and stellar winds above all. All STARKEY research products (calibrated stellar evolutionary tracks, isochrones, and bolometric corrections in all most relevant photometric systems, libraries of atmospheres and spectra of cool giants, dust-driven wind models, pulsation models for long-period variables) are provided to the astrophysics community through publicly accessible web tools.