Observational research on the variability and mass-loss in the AGB

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We have surveyed for variable stars in the Large and Small Magellanic Clouds (LMC, SMC) for 3 years with the near infrared camera SIRIUS equipped on IRSF in the South African Astronomical Observatory.We constructed Period-K magnitude diagrams of detected variable stars in the LMC and SMC. We found that variables in the SMC show the similar sequences previously discovered in the LMC. Furthermore, we discovered that the previously known sequence B consists of 2 sequences and that stars belonging to one of these sequences, named C', have the similar characteristics to those belonging to the sequence C. The stars in C and C' are thought to be the Mira variables pulsating in the fundamental and first overtone mode, respectively. We also found that the sequences A and the rest of B are separated into the upper (A+, B+) and lower (A-, B-) ones, respectively. Stars in A- and B- are probably variables in the Red Giant Branch (RGB) phase while A+ and B+ are in the Asymptotic Giant Branch (AGB). By comparing the sequence C in the LMC and SMC, we found that the period-K magnitude (period-luminosity) relation depend on the metallicity in that the variables in the SMC which has lower metallicity show systematically higher luminosity in the same period.From the observation of the intermediate-age globular cluster NGC 419 in the SMC, we found that the evolved AGB stars which is in the upper part of the AGB are all variables. However, only the tip AGB stars seem to increase their amplitudes with their colors and only the most evolved ones seem to become large amplitude Mira-like variables.