On spectra and colours of synthetic stellar populations

We compiled a library of integrated properties of stellar populations called BLoIS (Basel Library of Integrated Spectra) with the help of evolutionary synthesis algorithms developed by Gustavo Bruzual and Stéphane Charlot, using the theoretical stellar spectral library called BaSeL, which was constructed by François Cuisinier, Thibault Lejeune, and Pieter Westera.
By building up BLoIS we were able to study the effects of the different input parameters on the integrated properties (mainly spectra and colours) of synthetic stellar populations. We find that the slope of the Initial Mass Function (IMF) produces the largest effects, followed by the SFR, and the mass range of the IMF. Different stellar evolutionary tracks and different spectral libraries have only moderate effects.
The analysis of BLoIS showed that all population spectra and most of the population colours are unique, because the metallicity characterizes the spectra in a unique way. Comparisons amongst model populations confirmed that the IMF affects the integrated spectra and colours in the most sensitive way.
Furthermore, there is no absolute degeneracy between age and metallicity in BLoIS, but certain combinations of these parameters can lead to similar spectra and colours. However, we can confirm that these similarities are more pronounced at older ages and we can state that the degree of similarity depends on the position in the age-metallicity plane.
As a theoretical application we developed a least-squares algorithm to derive subpopulations from a composed population spectrum. In the framework of model populations this algorithm is able to recover the individual contributions of subpopulations to the total spectrum.
To put contraints on observatrions we developted Monte Carlo simulation programmes. Using those we found that the observations of old populations must be more accurate than observations of young populations in order to achieve the same confidence level in recovering the correct population.