post-AGB星的演化特征

The Evolution Characters of Post-AGB Stars

本文评述了低质量、低光度的post-AGB星的演化特征。post-AGB星是介于AGB相与PN相之间的特殊天体。在大多数post-AGB星的拱星包层中存在着大量尘埃,从它的辐射频谱中可以观测到强的过量的红外辐射。尘埃是由两个壳层组成的。冷的尘埃壳层分布在拱星包层的外层,它是由恒星在AGB相时质量损失所形成的。热的尘埃壳层分布在拱星包层的靠恒星很近的地方,它是在post-AGB中新近形成的。在Post-AGB星的拱星包层中还存在着许多分子,例如CO分子,OH、H_2O和SiO脉泽分子。它们在许多波段产生值得引起注意的射电辐射。post-AGB星常常表现为光度不变、表面温度大大增加的演化特征。

The evolution characters of post-AGB stars are reviewed in this paper, post-AGB stars are special objects, which are located at between AGB phase and PN phase. There is a lot of dust in their circumstellar envelops. The strong excess infrared radiation is observed from their spectra. Dust consists of two shells. Cold dust-shell is distributed on out-layer of circumstedlar envelop. It is formed because of mass loss of the star at AGB phase. Hot dust-shell is distributed in circumstellar envelop nearby the star. It is recently formed at post-AGB phase. There also is a lot of molecules in their circumstellar envelop, for example CO molecules, OH, H2O, and SiO maser molecules. It is considerable that they radiate radio wave at many qands. The evolution characters of post-AGB stars often appear to be constant luminosity, and great increase of their surface temperature.