Evolution of low- and intermediate-mass stars with [Fe/H]≤− 2.5
Evolution of low- and intermediate-mass stars with [Fe/H]≤− 2.5
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DOI：
10.1111/j.1365-2966.2010.16473.x
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发表时间：
2010-02
影响因子：
4.8
通讯作者：
T. Suda;M. Fujimoto
中科院分区：
文献类型：
--
作者：
T. Suda;M. Fujimoto
We present extensive sets of stellar models for 0.8 9.0M⊙ in mass and 5 6 [Fe/H] 6 2 and Z = 0 in metallicity. The present work focuses on the evolutionary characteristics of hydrogen mixing into the helium-flash convective zones during the core and shell helium flashes which occurs for the models with [Fe/H] . 2.5. Evolution is followed from the zero age main sequence to the thermally pulsating AGB phase including the hydrogen engulfment by the helium-flash convection during the RGB or AGB phase. There exist various types of mixing episodes of how the hydrogen mixing sets in and how it affects the final abundances at the surface. In particular, we find hydrogen ingestion events without dredge-ups that enables repeated neutroncapture nucleosynthesis in the helium flash convective zones with 13 C(α,n) 16 O as neutron source. For Z = 0, the mixing and dredge-up processes vary with the initial mass, which results in different final abundances in the surface. We investigate the occurrence of these events for various initial mass and metallicity to find the metallicity dependence for the helium-flash driven deep mixing (He-FDDM) and also for the third dredge-up events. In our models, we find He-FDDM for M 6 3M⊙ for Z = 0 and for M . 2M⊙ for 5 6 [Fe/H] 6 3. On the other hand, the occurrence of the third dredge-up is limited to the mass range of � 1.5M⊙ to � 5M⊙ for [Fe/H] = 3, which narrows with decreasing metallicity. The paper also discusses the implications of the results of model computations for observations. We compared the abundance pattern of CNO abundances with observed metal-poor stars. The origins of most iron-deficient stars are discussed by assuming that these stars are affected by binary mass transfer. We also point out the existence of a blue horizontal branch for 4 . [Fe/H] . 2.5.
