INVESTIGATING [X/FE], IMF AND COMPOSITENESS IN INTEGRATED MODELS
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This dissertation explores several existing challenges of evolutionarystellar population synthesis models in integrated light:age-metallicity degeneracy, initial mass function (IMF), elementalabundances, and compositeness. First, we search for age-sensitive andmetal-sensitive colors in three photometric systems. We also add tothe discussion of optical to near-infrared Johnson-Cousins broad bandcolors, finding a great decrease in age sensitivity when updatedisochrones are used. Then we investigate the element abundances andcompositeness of our models, in which we assume a single-peakabundance distribution and the same elemental abundance trends as theMilky Way bulge stars. Varying the width of the abundancedistribution function reveals novel ``red lean'' and ``red spread''effects. Next, we study three effects that co-determine thedwarf/giant ratio: the IMF slope, the IMF low mass cut-off (LMCO), andAGB star contributions. This degeneracy can be lifted for old,metal-rich stellar populations, although at an observationallychallenging level ($\approx$0.02 mag). Finally, we select and reducemore than 200 $z\sim0.4$ red galaxy spectra from the DEEP2 sky survey,and measure the Lick-style spectral indices from the compositespectra. Multiple optical IMF-sensitive indices suggest a shallowerIMF that qualitatively agrees with current literature.