Age Metallicity Relation in the LMC

Abstract

The age metallicity relation (AMR) is known to be very important for understanding the chemical evolution in a galaxy. LMC, our nearest galaxy offers an ideal target for such studies, considering that with the SMC and our Galaxy are an interacting group, influencing each other's star formation rate and production of metals. An observing program for the determination of AMR from a study of small open LMC clusters using Stroemgren phorometry has been initiated. Three observing runs were granted with the 1.5m Danish Telescope at La Silla. We report on our search within 8 clusters, scattered all over the LMC to cover a wide spatial distribution and metallicity. CMDs using Stroemgren photometry have been produced, in order to find the age of the stellar content. The available isochrones used, although very few are able to give us a good age estimate. The calibration of the y, b, v, magnitudes and colours to metallicity used, is the one by Richter et al.(A&A, 1999), to obtain the adopted metallicities of the clusters. Although our sample is still small, a clear trend is observed in AMR showing a significant increase of metallicity with age. Comparison with previous AMRs from other investigations shows good agreement within the errors. The bursting model of chemical evolution by Pagel and Tautvaisiene (MNRAS, 1999) shows that the burst of star formation (SF) produces a change of slope in their AMRs from 2 Gyr to the present time, the burst assumed to occur from –0.4 dex to 0.0 dex. Although our sample is small the observed trend favours the expected change of the AMRs rather towards the 1 Gyr. Therefore our observations support a bursting model of chemical evolution. More obervations are needed and new theoretical models to strengthen these results. Finally it is found that all young metal rich clusters occupy the central LMC regions whereas the old metal poor ones are found in the LMC periphery giving evidence for a metallicity gradient as well. We would like to acknowledge financial support by the NATO grant GRG.GRGP/972234and the Greek Secretariat of Research and Technology.