Potential of colors for determining age and metallicity of stellar populations

¹ National Astronomical Observatories/Yunnan Observatory, the Chinese Academy of Sciences, Kunming, 650011, PR China e-mail: zhongmu.li@gmail.com
² Graduate School of the Chinese Academy of Sciences, PR China

Received: 4 September 2006
Accepted: 4 December 2006

Abstract

Context.Colors are usually not used for constraining stellar populations because they are thought to have the well-known age-metallicity degeneracy, but some recent works show that colors can also be used. A simple stellar population synthesis model is widely used, but there is no analysis for its colors.

Aims.We try to find colors that can potentially be used to determine the age and metallicity of stellar populations by the standard model.

Methods.Principal component analysis and relative sensitive parameter techniques are used in this work.

Results., , , , , , , and are found to be more important for studying populations than others. Pairs of colors such as and are found to be able to disentangle the stellar age-metallicity degeneracy via the high-resolution model, while pairs such as and may be used instead when the low-resolution model is used. Furthermore, the and colors of the low-resolution 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.