Potential colors for determining age and metallicity of stellar populations

Context. Colors are usually not used for constraining stellar populations because they are thought to have the well-known agemetallicity degeneracy. But some recent works show that colors can also be used. The simple stellar population (SSP) synthesis model of Bruzual & Charlot (2003) (BC03) is widely used but there is no analysis for its colors. Aims. We try to find colors which can potentially be used to determine the age and metallicity of stellar populations by the standard model of BC03. Methods. Principal component analysis (PCA) and relative sensitive parameter techniques are used in this work. Results. U − K, U − H, U − J, B− K, B− H, U − I, B− J and V − K are found to be more important to study populations than others. Pairs of colors such as B−K and B−V are found to be able to disentangle the stellar age-metallicity degeneracy via the high-resolution BC03 model, while pairs such as U − K and R− I may be used instead when the low-resolution model is used. Furthermore, the u− g and r − i colors of low-resolution BC03 model seem to have the same potential but there are no such colors for the high-resolution one. Conclusions. Some colors have been shown to have the potential to determine the age and metallicity of stellar populations, but relative metallicity and age sensitivities of colors in different stellar population synthesis models are usually different. In addition, minor star formations will make star systems look younger and more metal rich than their dominating populations.