Red Giant Stars in the Large Magellanic Cloud Clusters

We present deep J,H,Ks photometry and accurate Color Magnitude Diagrams downto K ~18.5, for a sample of 13 globular clusters in the Large Magellanic Cloud.This data set combined with the previous sample of 6 clusters published by ourgroup gives the opportunity to study the properties of giant stars in clusterswith different ages (ranging from ~80 Myr up to ~3.5 Gyr). Quantitativeestimates of star population ratios (by number and luminosity) in theAsymptotic Giant Branch, the Red Giant Branch and the He-clump, have beenobtained and compared with theoretical models in the framework of probing theso-called phase transitions. The AGB contribution to the total luminositystarts to be significant at ~200 Myr and reaches its maximum at ~5-600 Myr,when the RGB Phase Transition is starting. At ~900 Myr the full developing ofan extended and well populated RGB has been completed. Both the occurrence ofthe AGB and RGB Phase Transitions are sharp events, lasting a few hundreds Myronly. These empirical results agree very well with the theoretical predictionsof simple stellar population models based on canonical tracks and thefuel-consumption approach.Comment: 32 pages, 11 figures, accepted to Ap