Metallicity estimates for old star clusters in M 33

Abstract

Using the theoretical stellar population synthesis models of BC96, Kong et al. (2003) showed that some BATC colors and color indices could be used to disentangle the age and metallicity effect. They found that there is a very good relation between the flux ratio of L8510/L9170 and the metallicity for stellar populations older than 1 Gyr. In this paper, based on the Kong et al. results and on the multicolor spectrophotometry of Ma et al. (2001, 2002a,b,c), we estimate the metallicities of 31 old star clusters in the nearby spiral galaxy M 33, 23 of which are "true" globular clusters. The results show that most of these old clusters are metal poor. We also find that the ages and metal abundance for these old star clusters of M 33 do not vary with deprojected radial position.