Study of the evolution of the structure of circumstellar dust envelopes based on the observations of infrared spectra

该项目的科学目标是通过研究演化阶段与星周尘埃包层（CDE）结构之间的关系来阐明渐近巨星分支（AGB）恒星的演化。在这个项目开始的时候，我们就认为通过观测来追踪CDE结构的演化变化是非常重要的。因此，我们在近红外（NIR）波长区域观测到了多种具有CDE的AGB恒星。根据这一观测结果，我们发现碳星（AGB恒星的一种）的空间分布可能不同于具有厚cde的富o AGB恒星。这一结果表明，AGB恒星的演化过程可能取决于其在银河系中所处的位置，这是由于位置所决定的物理条件的差异所导致的。因此，我们在近红外波段新观测到银河系中约450颗碳星，阐明了碳星与富含o的AGB星在空间分布上的差异。我们的观测结果表明，碳恒星的空间分布与富含o的AGB恒星不同，AGB恒星的演化过程取决于其在银河系中的位置。

The scientific objective of this project is to clarify the evolution of asymptotic giant branch (AGB) stars by investigating the relation between evolutionary stages and the structure of circumstellar dust envelopes (CDE). At the beginning of this project, we consicered that it is very important to trace the evolutionary change of the structure of CDE observationally. Thus we observed variety of AGB stars with CDE in the near-infrared (NIR) wavelength region. As this observational results, we found that the space distribution of carbon stars (one kind of AGB stars) is likely to be different from that of O-rich AGB stars with thickCDE.This result indicate that the evolutionary process of AGB stars may depend on the location in the Galaxy caused by some difference in the physical condition which depends on the location. Thus we have newly observed about 450 carbon stars in the Galaxy in the NIR to clarify the difference in the space distribution of carbon stars from that of O-rich AGB stars. Our observed results suggest that the space distribution of carbon stars is different from that of O-rich AGB stars and that the evolutionary process of AGB stars depend on the location in the Galaxy.