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

利用安装在南非天文台IRSF上的天狼星近红外相机对大小麦哲伦星云(LMC，SMC)中的变星进行了3年的观测，绘制了LMC和SMC中探测到的变星的周期-K等图。我们发现，SMC中的变量显示了先前在LMC中发现的相似序列。此外，我们还发现已知的序列B由两个序列组成，属于其中一个序列C‘的恒星与属于序列C的恒星具有相似的特征。C和C’中的恒星分别被认为是以基频模式和第一泛音模式脉动的Mira变星。我们还发现，序列A和B的其余部分分别被分为上部(A+，B+)和下部(A-，B-)序列。A-和B-中的恒星可能是红巨星分支(RGB)阶段的变星，而A+和B+恒星可能是渐近巨星分支(AGB)阶段的变星。通过比较LMC和SMC中的序列C，我们发现周期-K星等(周期-光度)关系依赖于金属丰度，因为在同一周期中，金属丰度较低的SMC中的变星系统地表现出较高的光度；通过对SMC中的中龄球状星团NGC419的观测，我们发现AGB上演化的AGB星都是变星。然而，只有尖端的AGB恒星似乎会随着它们的颜色增加它们的振幅，而且只有最进化的恒星似乎才会变成类似米拉的大振幅变星。

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.