Red giant stars in the large magellanic cloud clusters

We present deep J, H, and Ks photometry and accurate color magnitude diagrams down to K ≈ 18.5 for a sample of 13 globular clusters in the Large Magellanic Cloud. This data set combined with the previous sample of six clusters published by our group gives the opportunity to study the properties of giant stars in clusters with different ages (ranging from ~80 Myr up to 3.5 Gyr). Quantitative estimates of star population ratios (by number and luminosity) in the asymptotic giant branch (AGB), the red giant branch (RGB), and the He clump have been obtained and compared with theoretical models in the framework of probing the so-called phase transitions. The AGB contribution to the total luminosity starts to be significant at ≈200 Myr and reaches its maximum at 500-600 Myr, when the RGB phase transition is starting. At ≈900 Myr the full development of an extended and well-populated RGB has been completed. The occurrences of both the AGB and RGB phase transitions are sharp events, lasting a few hundred megayears only. These empirical results agree very well with the theoretical predictions of simple stellar population models based on canonical tracks and the fuel-consumption approach.