Evolution of Low- and Intermediate-Mass Stars with Fe-H <= -2.5 - Astrophysics > Astrophysics of GalaxiesReport as inadecuate




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Abstract: We present extensive sets of stellar models for 0.8-9.0Msun in mass and -5 <=Fe-H <= -2 and Z = 0 in metallicity. The present work focuses on theevolutionary characteristics of hydrogen mixing into the He-flash convectivezones during the core and shell He flashes which occurs for the models withFe-H <~ -2.5. Evolution is followed from the zero age MS to the TPAGB phaseincluding the hydrogen engulfment by the He-flash convection during the RGB orAGB phase. There exist various types of mixing episodes of how the H mixingsets in and how it affects the final abundances at the surface. In particular,we find H ingestion events without dredge-ups that enables repeatedneutron-capture nucleosynthesis in the He flash convective zones with 13Ca,n16 O as neutron source. For Z = 0, the mixing and dredge-up processesvary with the initial mass, which results in different final abundances in thesurface. We investigate the occurrence of these events for various initial massand metallicity to find the metallicity dependence for the He-flash driven deepmixing He-FDDM and also for the third dredge-up TDU events. In our models,we find He-FDDM for M <= 3Msun for Z = 0 and for M <~ 2Msun for -5 <~ Fe-H <~-3. On the other hand, the occurrence of the TDU is limited to the mass rangeof ~1.5Msun to ~5Msun for Fe-H = -3, which narrows with decreasingmetallicity. The paper also discusses the implications of the results of modelcomputations for observations. We compared the abundance pattern of CNOabundances with observed metal-poor stars. The origins of most iron-deficientstars are discussed by assuming that these stars are affected by binary masstransfer. We also point out the existence of a blue horizontal branch for -4 <~Fe-H <~ -2.5.



Author: Takuma Suda, Masayuki Y. Fujimoto

Source: https://arxiv.org/



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