Trace elements and evolution of PG 1159 stars

对热的富氦后AGB恒星的现代光谱分析改善了我们对它们演化的看法：它们可能是所谓的“再次出现的后AGB”恒星。然而，我们的分析结果与标准进化计算的预测不一致：这些结果显示了被厚厚的氦和氢壳层覆盖的大气层深处所观察到的丰度模式，因此，远远无法观察到。新开发的进化模型现在可以预测这些丰度。光球中氢、氮、氖的含量是检验这些计算的重要指标，也是这些恒星进一步演化的制约因素。

Modern spectral analysis of hot helium-rich post-AGB stars has improved our picture of their evolution: They are likely so-called "born-again post-AGB" stars. However, the results of our analyses had been inconsistent with predictions of standard evolutionary calculations: These had shown the observed abundance pattern deep inside the atmosphere covered by thick helium and hydrogen shells and thus, far from being observable. Newly developed evolutionary models can predict now these abundances. The photospheric hydrogen, nitrogen and neon content are important indicators to test these calculations and to give constraints for the further evolution of these stars.