Observational study on the evolution of AGB stars and their mass-loss

众所周知，与麦哲伦星云（MCs）相关的球状星团（GCs）是恒星演化理论的理想试验场，因为它可以估计恒星的基本参数，如质量、光度、金属丰度等。利用南非天文台（SAAO）新建的1.4 m望远镜IRSF和近红外相机SIRIUS对MCs中的GCs进行了重复观测，得到了以下结果：我们发现AGB上部的恒星都表现出变异性，它们的周期和振幅沿AGB方向增加。在AGB的顶端，恒星变成了离子周期变量，可能是Mira型。质量损失似乎不是沿着AGB发生的，而是发生在某个特殊的阶段，可能是在很晚的阶段。虽然我们发现了许多变星，但我们无法探测到短周期和可能的低振幅变星，因为我们的观测机会并不密集。这种变率何时出现，如何沿AGB方向演变，以及光度与周期之间的关系仍有待进一步研究。

It is well known that globular clusters (GCs) associated with the Magellanic Clouds (MCs) are an ideal test field for the theory of stellar evolution because fundamental parameters of a star such as the mass, luminosity, metallicity, etc. can be estimated. We performed repeated observations of GCs in the MCs at South African Astronomical Observatory (SAAO) with a newly built 1.4 m telescope, IRSF and a near-infrared camera, SIRIUS and obtained the following results.1. We found that stars in the upper AGB all show variabilities and their periods and ampitudes tend to increase along AGB. At the tip of the AGB, stars turn to be Ions period variables, possibly Mira types.2. The mass-loss does not seem to occur along AGB but occur in a some special phase, probably in a very late phase.Although we found many variable stars, we could not detect short-period and possibly low amplitude variables because our observational chances were not dense. When the variability appears and how it evolves along AGB and the relationship between the luminosity and period along AGB still remains a future work.